When assessing vibration from freight train operations, consider the locomotive and rail car vibration separately. Since locomotive vibration lasts for a very short time, it can be characterized by the infrequent events category in Table 6-2. Rail car vibration from a typical line -haul freight train usually lasts for several minutes and can be characterized by the frequent events category in Table 6-2. Note xii Vibration is abbreviated as "vib." in this flowchart. 4895
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that locomotives often create vibration levels that are 3 to 8 dB higher than those created by rail cars.
Use good engineering judgment to confirm the approach is reasonable for each project. For example, some spur rail lines carry very little rail traffic (sometimes only one train per week) or have short trains, in which case it may not be necessary to evaluate for impact. If there is uncertainty in how to determine the appropriate criteria, contact the FTA Regional office.
Decisions to relocate freight tracks closer to vibration -sensitive sites should be made with the understanding that increased vibration due to freight rail may not be possible to mitigate. Freight rail vibration may not always be successfully mitigated by the same methods as rail transit systems.
Option B: Vibration Impact Criteria for a Detailed Vibration Analysis
Determine the appropriate impact criteria for ground -borne vibration and ground -borne noise for a Detailed Vibration Analysis.
Step I: Ground -Borne Vibration
Choose the appropriate criteria based on Figure 6-2 and Table 6-6.
Ground -borne vibration criteria presented in this section are more detailed than in the General Vibration Assessment. The criteria are based on international standards for the effects of vibration on people related to annoyance and interference with activities in buildings(39) as well as industry standards for vibration -sensitive equipment.(46) The criteria in this section are used to assess the potential for interference or annoyance from building response and to determine performance of vibration reduction methods. Note that for highly -sensitive equipment, specific vibration criteria provided by the manufacturer supersede the criteria in this section.
The criteria are presented by category in Figure 6-2 and are defined by international and industry standards.(39)(46) These criteria define limits for acceptable maximum rms vibration velocity level with a one -second averaging time at the floor of the receiving building in terms of a one-third octave band frequency spectrum. Band levels that exceed a particular criterion curve indicate impact; and therefore, mitigation options should be evaluated considering the specific frequency range in which the treatment is most effective. Interpretations of the criteria are presented in Table 6-6.
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100
90 80
v
J
70 .61
a
60 50
40 Workshop
Office
Residential (Day)
Residential (Night)
VC -A
VC -B
VC -C
VC -D
VC -E
4 5 6.3 8 10 12.5 16 20 25 31.5 40 50 63 80
One Third Octave Band Center Frequency, Hz
Figure 6-2 Criteria for Detailed Vibration Analysis
Table 6-6 Interpretation of Vibration Criteria for Detailed Vibration Analysis Criterion
Curve
Max Lv,*
VdB
Description of Use
Workshop (ISO)
90 Vibration that is distinctly felt. Appropriate for workshops and similar areas not as sensitive to vibration.
Office (ISO)
84 Vibration that can be felt. Appropriate for offices and similar areas not as sensitive to vibration.
Residential Day
(ISO)
78 Vibration that is barely felt. Adequate for computer equipment and low - power optical microscopes (up to 20X).
Residential Night,
Operating Rooms
(ISO)
72 Vibration is not felt, but ground -borne noise may be audible inside quiet rooms. Suitable for medium -power optical microscopes (I 00X) and other equipment of low sensitivity.
VC -A
66 Adequate for medium- to high -power optical microscopes (400X), microbalances, optical balances, and similar specialized equipment.
VC -B
60 Adequate for high -power optical microscopes (I 000X) and inspection and lithography equipment to 3 -micron line widths.
VC -C
54 Appropriate for most lithography and inspection equipment to I -micron detail size.
VC -D
48 Suitable in most instances for the most demanding equipment, including electron microscopes operating to the limits of their capabilities.
VC -E
42 The most demanding criterion for extremely vibration -sensitive equipment.
As measured in I/3 -octave bands of frequency over the frequency range 8 to 80 Hz. 4897
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In addition to the uses described in Table 6-6, the detailed vibration criteria can be applied to the three land use categories presented in Table 6-3. ■ For residential land uses (category 2), use the residential night criterion curve in Table 6-6.
■ For institutional uses (category 3), use the residential day criterion curve in Table 6-6.
■ For category I, the specific use of the building should be matched to the appropriate criterion curve in Table 6-6.
■ For special buildings, such as those found in Table 6-4, either the criteria in Table 6-4 or specific criteria presented by the building operator should be used.
These criteria use a frequency spectrum because vibration -related problems generally occur due to resonances of the structural components of a building or vibration -sensitive equipment. Resonant response is frequency -dependent. A Detailed Vibration Analysis can provide an assessment that identifies potential problems resulting from resonances.
The detailed vibration criteria are based on generic cases when people are standing or equipment is mounted on the floor in a conventional manner.
Consequently, the criteria are less stringent at very low frequencies below 8 Hz.
Where special vibration isolation has been provided in the form of pneumatic isolators, the resonant frequency of the isolation system is very low.
Consequently, in this special case, the curves may be extended flat at lower frequencies.
Step 2: Ground -borne Noise
Ground -borne noise impacts are assessed based on criteria for human annoyance and activity interference. The Detailed Vibration Analysis procedure provides vibration spectra inside a building. To evaluate ground -borne noise, convert these vibration spectra to sound pressure level spectra in the occupied spaces using the method described in Section 6.5 and compare to the criteria as follows:
■ For residential buildings, use the criteria presented in Table 6-3. ■ For special buildings listed in Table 6-4, A -weighted noise may not be sufficient to assess activity interference for a Detailed Vibration Analysis.
Each special building may have a unique specification for acceptable noise levels and criteria must be determined on a case -by -case basis.
For example, a recording studio may have stringent requirements for allowable noise in each frequency band.
6.3 Evaluate Impact: Vibration Screening
Procedure
Determine the potential for impact using the Vibration Screening Procedure by identifying any vibration -sensitive land uses (Table 6-I) within the appropriate screening distance.
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no
yes
No Vibration
Impact Likely
No Further
Analysis Required
Start
Steel -Wheel
Steel -Rail
Project?
no
Vib.
Sensitive
Manufacturing or
Research
no
Vehicles
Operating in
Building?
no
yes
yes
no
Determine Screening
Distances Based on
Project Type and
Land use Categories
Sensitive
Land Uses within
Impact Distances?
yes
Vibration Analysis
Required
Figure 6-3 Flow Chart of Vibration Screening Process
Step I: Classify Project Vehicles
Determine the project type and the next step based on the guidelines below.
Option A: No Vehicles — Transit projects that do not involve vehicles do not have potential for vibration impact and do not require further analysis (Box A in Figure 6-3).
Many smaller FTA-funded projects, such as bus terminals, park -and -ride lots, and station rehabilitation are in this category, and do not require further analysis of ground -borne vibration impact. However, if track systems are modified (e.g., tracks moved or switches modified), proceed to Step 2.
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Option B: Steel-wheeled/Steel-rail Vehicles — Transit projects with steel- wheeled/steel-rail vehicles have potential for vibration impact (Box B in Figure 6-3); proceed to Step 2. These rail systems include urban rapid transit, LRT, commuter rail, and steel -wheel intermediate capacity transit (ICT) systems.
Option C: Rubber -tire Vehicles — For projects that involve rubber -tire vehicles and do not meet the following conditions, vibration impact is unlikely, and no further analysis is needed. Proceed to Step 2 for projects that involve rubber -tire vehicles and meet the following conditions (Box A in Figure 6.3):
■ Roadway irregularity — Expansion joints, speed bumps, or other design features that result in unevenness in the road surface can result in perceptible ground -borne vibration at distances up to 75 ft away. ■ Operation close to vibration -sensitive buildings — Buses, trucks, or other heavy vehicles operating close to a vibration -sensitive building (within approximately 100 ft from the property line) may impact vibration -sensitive activities, such as research that uses electron microscopes or manufacturing of computer chips.
■ Vehicles operating within buildings — Special considerations are often required for shared use facilities where vehicles operate inside or directly underneath buildings such bus stations located inside an office building complex.
Step 2: Determine Project Type
Determine the project type according to Table 6-7.
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Table 6-7 Project Types for Vibration Screening Procedure Project Type
Number
Project
Type
Description
I
Conventional
Commuter
Railroad
Both locomotives and passenger vehicles create vibration. For commuter trains, the highest vibration levels are typically created by the locomotives.
Electric commuter rail vehicles create levels of ground -borne vibration that are comparable to electric rapid transit vehicles.
2 RRT
Ground -borne vibration impact from rapid transit trains is one of the major environmental issues for new systems. Ground -borne vibration is usually a major concern for subway operations. It is less common for at -grade and elevated rapid transit lines to create intrusive ground -borne vibration and noise since air -borne noise typically dominates.
3 LRT and
Streetcars
The ground -borne vibration characteristics of light rail systems are very similar to those of rapid transit systems. Because the speeds of light rail systems are usually lower, typical vibration levels are usually lower. Steel-wheel/steel-rail AGT is included in either this category or the ICT category depending on the level of service and train speeds.
4 Intermediate
Capacity
Transit
Because of the low operating speeds of most ICT systems, vibration problems are not common. However, steel -wheel ICT systems that operate close to* vibration -sensitive buildings have the potential of causing intrusive vibration.
With a stiff suspension system, an ICT system could create intrusive vibration. 5 Bus and
Rubber -Tire
Transit
Projects
This category encompasses most projects that do not include steel -wheel trains of some type. Examples include diesel buses, electric trolley buses, and rubber -tired people movers. Most projects that do not include steel -wheel trains do not cause vibration impacts.**
*See the screening distances for category I land uses in Table 6-8. ** Most complaints about vibration caused by buses and trucks are related to rattling of windows or items hung on the walls.
These vibrations are usually the result of airborne noise and not ground -borne vibration. In the case where ground -borne vibration is the source of the complaint, the vibration can usually be attributed to irregularities in the road.
Step 3: Determine Screening Distance
Determine the appropriate screening distances based on land use and project type according to Table 6-8.
The distances are based on the criteria presented in Section 6.3, the procedures in Section 6.4 assuming normal vibration propagation, and include a 5 -dB factor of safety. Even so, areas with very efficient vibration propagation can have substantially higher vibration levels.
Because of the 5 -decibel safety factor, the screening distances will identify most of the potentially impacted areas, even for areas with efficient propagation.
However, when there is evidence of efficient propagation, such as previous complaints about existing transit facilities or a history of problems with construction vibration, increase the distances in Table 6-8 by a factor of 1.5. 4901
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Table 6-8 Screening Distances for Vibration Assessments Type of Project
Critical Distance for Land Use Categories*
Distance from ROW or Property Line, ft
Land Use
Cat. I
Land Use
Cat. 2
Land Use
Cat. 3
Conventional Commuter Railroad
600
200
120
RRT
600
200
120
LRT and Streetcars
450
150
100
ICT
200
I00
50 Bus Projects (if not previously screened out)
100
50 --
*For the Vibration Screening Procedure, evaluate special buildings as follows: Category I - concert halls and TV studios, Category 2 - theaters and auditoriums
Step 4: Identify Vibration -Sensitive Land Uses
Identify all vibration -sensitive land uses (Table 6- I) within the chosen screening distance. If no vibration -sensitive land uses are identified, no further vibration analysis is needed. If one or more of the vibration -sensitive land uses are in the screening distance, complete a General Vibration Assessment (Section 6.4) or a Detailed Vibration Analysis (Section 6.5).
6.4 Evaluate Impact: General Vibration
Assessment
Evaluate for impact using the General Vibration Assessment procedure if the Vibration Screening Procedure (Section 6.3) identified vibration -sensitive receivers within the screening distance of the transit vibration source.
For guidelines on when the General Vibration Assessment is appropriate, review Section 6. I .
The basic approach for the General Vibration Assessment is to define a curve or set of curves that predicts the overall ground -borne vibration as a function of distance from the source, then apply adjustments to these curves to account for factors such as vehicle speed, geologic conditions, building type, and receiver location within the building. When the vehicle type is not covered by the curves included in this section, it will be necessary to define an appropriate curve either by extrapolating from existing information or performing measurements at an existing facility.
Step I: Select Base Curve for Ground Surface Vibration
Level
Select a standard vibration curve to represent general vibration characteristics for the source.
The curves presented in Figure 6-4 are based on measurements of ground - borne vibration at representative North American transit systems and can be used to represent vibration characteristics for standard transportation systems in the General Vibration Assessment.
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These curves assume typical ground -borne vibration levels, equipment in good condition, and speeds of 50 mph for the rail systems and 30 mph for buses.
Adjustments to account for differences in speed and geologic conditions are included in Step 2.
Select a base curve from Figure 6-4 according to the guidelines in Table 6-9.
Equations for the curves in Figure 6-4 are included in Table 6-10. Additional considerations for selecting a base curve for systems not included in Table 6-9 are presented below by transit mode.
Table 6-9 Ground Surface Vibration Level Base Curve Descriptions Curve
Description
Locomotive -Powered
Passenger or Freight Curve
Appropriate for vehicles powered by diesel or electric locomotives including intercity passenger trains and commuter rail trains.
Rapid Transit or Light Rail
Vehicles Curve
Appropriate for both heavy and light -rail vehicles on at -grade and subway track.
Rubber -Tired Vehicles Curve
Appropriate for rubber -tire vehicles. These types of vehicles rarely create ground -borne vibration problems unless there is a discontinuity or bump in the road that causes the vibration. This curve represents the vibration level for a typical bus operating on smooth roadway.
RMS Velocity level, VdB re 1 micro in./sec
100
95 90
85 80
75 70
65 60
55 50
Locomotive Powered
Passenger or Freight
(50 mph)
Rubber -Tired
Vehicles
(30 mph)
Rapid Transit or
Light Rail Vehicles _
(50 mph)
150 200
10 20 30 40 50 60 80 100
Distance from track centerline, ft
(Use diagonal distance for underground systems)
Figure 6-4 Generalized Ground Surface Vibration Curves
300
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Table 6-IO Generalized Ground Surface Vibration Equations Curve
Equation
Locomotive Powered
Passenger or Freight Curve
L„ = 92.28 + 14.83 log(D) — 14.17log(D)2
+1.65 log(D)3
Eq. 6-I
Transit or Light Rail
Vehicles Curve
L„ = 85.88 — 1.06 log(D) — 2.32 log(D)2
—0.87 log(D)3
Eq. 6-2
Rubber Tired Vehicles Curve
L„ = 66.08 + 34.28 log(D) — 30.25 log(D)2
+5.40 log(D)3
Eq. 6-3
L„ = velocity level, VdB
D = distance, ft
Considerations for selecting a base curve for different transit modes include:
• Intercity passenger trains — Although intercity passenger trains can be an important source of environmental vibration, it is rare that they are considered for FTA-funded projects unless a new transit mode uses an existing rail alignment. When a new transit line uses an existing rail alignment, changes in the intercity passenger traffic can result in either positive or negative impacts. Use the locomotive -powered passenger or freight curve for intercity passenger trains unless there are specific data available on the ground -borne vibration created by the new train operations.
• Locomotive -powered commuter rail — Use the locomotive - powered passenger or freight curve for all commuter rail system powered by either diesel or electric locomotives.
• Electric multiple unit (EMU) — Use the rapid transit or light rail vehicles curve for self -powered electric commuter rail trains. • Diesel multiple unit (DMU) — Self -powered DMUs create vibration levels somewhere between rapid transit vehicles and locomotive - powered passenger trains. A vibration curve for DMUs can be estimated by lowering the locomotive -powered passenger or freight curve by 5 dB.
• Subway heavy rail or light rail — Use the rapid transit or light rail vehicles curve for subway heavy rail and subway light rail. Although vibrations from subway and at -grade tracks have very different characteristics, the overall vibration velocity levels are comparable.
When applied to subways, the rapid transit or light rail vehicles curve assumes a relatively lightweight bored concrete tunnel in soil. The vibration levels will be lower for heavier subway structures such as cut - and -cover box structures and stations.
• At -grade heavy rail or light rail — Use the rapid transit or light rail vehicles curve for at -grade heavy rail or light rail. Heavy rail and LRT vehicles have similar suspension systems and axle loads and create similar levels of ground -borne vibration.
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• Elevated guideways or aerial structures — Vibration from operations on an elevated structure is typically not an issue unless the guideway is supported by a building or located very close to buildings.
Apply the appropriate adjustment for the aerial structures (Section 6.4, Step 2).
■ Streetcars — Use the rapid transit or light rail vehicles curve for street cars.
• ICT — Use the rapid transit or light rail vehicles curve for ICT systems with steel wheels and the rubber -tired vehicles curve for ICT systems with rubber tires.
• Other vehicle types — For less common modes such as magnetically - levitated vehicles (maglev), monorail, or AGT, use good engineering judgment to choose a standard curve to best fit the mode or if a new curve needs to be developed, as a function of distance from the track.
Examples include:
▪ Vibration from a rubber -tire monorail operating on aerial guideway can be approximated using the rubber -tired vehicles curve with the appropriate adjustment for the aerial structure (Section 6.4, Step 2).
▪ Most of the data available on the noise and vibration characteristics of maglev vehicles comes from high-speed systems intended for inter -city service. Even though there is no direct contact between the vehicle and the guideway, the dynamic loads on the guideway can generate ground -borne vibration. Measurements on a German high-speed maglev
resulted in ground -borne vibrations at 75 mph which is comparable to the base curve for rubber -tired vehicles at 30 mph.(49)
Step 2: Apply Adjustments
Apply project -specific adjustments to the standard vibration curve.
Once the base curve has been selected, use the adjustments in the following instructions to develop project -specific vibration projections at each receiver.
All adjustments are given as single numbers to add to, or subtract from, the base level.
Adjustments are separated by source, path, and receiver and include speed, wheel and rail type and condition, type of track support system, type of building foundation, and number of floors above the basement level. Calculate the appropriate adjustments to the base level. An example of the General Vibration Assessment is provided at the end of this Section.
It should be recognized that many of these adjustments are strongly dependent on the frequency spectrum of the vibration source and the frequency dependence of the vibration propagation. The adjustments in this section are suitable for generalized evaluation of the vibration impact and vibration 4905
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mitigation measures because they are based on typical vibration spectra.
However, these adjustments are not adequate for detailed evaluations of impact of vibration -sensitive buildings or for detailed specification of mitigation measures.
2a. Apply source adjustments to the base curve using Table 6- I I and the descriptions below to account for the project -specific source characteristics.
Table 6- I I Source Adjustment Factors for Generalized Predictions of GB Vibration and Noise Source
Factor
Adjustment to
Propagation Curve
Comment
Speed
Vehicle
Reference
50 mph
Speed
30 mph
Vibration level is approximately proportional to
201og(speed/speed,ef), see Eq. 6-4.
Speed
+ I.6 dB
0.0 dB
1.9 dB
-4.4 dB
-8.0 dB
+6.0 dB
+4.4 dB
+2.5 dB
0.0 dB
-3.5 dB
60 mph
50 mph
40 mph
30 mph
20 mph
Vehicle Parameters (not additive, apply greatest value only) Vehicle with
stiff primary
suspension
+8 dB
Transit vehicles with stiff primary suspensions have been shown to create high vibration levels. Include this
adjustment when the primary suspension has a vertical
resonance frec uency greater than 15 Hz.
Resilient
Wheels
0 dB
Resilient wheels do not generally affect ground -borne
vibration except at frequencies greater than about 80
Hz.
Worn Wheels
or Wheels with
Flats
+10 dB
Wheel flats or wheels that are unevenly worn can cause
high vibration levels.
Track Conditions (not additive, apply greatest value only) Worn or
Corrugated
Track
+10 dB
Corrugated track is a common problem. Mill scale* on
new rail can cause higher vibration levels until the rail has been in use for some time. If there are adjustments for vehicle parameters and the track is worn or
corrugated, only include one adjustment.
Special
Trackwor
within within 200 ft
+10 dB (within 100 ft)
+5 dB (between 100 and 200 ft)
Wheel impacts at special trackwork will greatly increase vibration levels. The increase will be less at greater
distances from the track. Do not include an adjustment
for special trackwork more than 200 ft away.
Jointed Track
+5 dB
Jointed track can cause higher vibration levels than
welded track.
Uneven Road
Surfaces
+5 dB
Rough roads or expansion joints are sources of
increased vibration for rubber -tire transit.
Track Treatments (not additive, apply greatest value only) Floating Slab
rFl ackbed
T the
-15 dB
The reduction achieved with a floating slab trackbed is strongly dependent on the frequency characteristics of
vibration.
Ballast Mats
I0 dB
Actual reduction is strongly dependent on frequency of
vibration.
High -Resilience
Fasteners
-5 dB
Slab track with track fasteners that are very compliant in the vertical direction can reduce vibration at frequencies greater than 40 Hz.
*Mill scale on a new rail is a slightly corrugated condition caused by certain steel mill techniques.
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In addition to the comments in Table 6-11, use the following guidelines to select the appropriate adjustment factors. Some adjustments in the same category are not cumulative (additive) and only the greatest applicable adjustment should be applied. The adjustments that are not additive are noted in Table 6- I I and in the descriptions below. Note that some adjustments are not additive across multiple categories and are noted in the comments of Table 6- I I . For example, the adjustment for a vehicle with stiff primary suspension is 8 dB, and the adjustment for wheel flats is I 0 dB. If the vehicle has a stiff primary suspension and has wheel flats, the projected vibration levels should be increased by 10 dB, not 18 dB.
In addition, some vibration control measures are targeted for specific frequency ranges. The shape of the actual vibration spectra should be considered so that an appropriate vibration control measure may be selected. • Speed — The levels of ground -borne vibration and noise vary, approximately, as 20 times the logarithm of speed. This means that doubling train speed will increase the vibration levels approximately 6 dB, and halving train speed will reduce the levels by 6 dB. The adjustments in Table 6- I I have been tabulated for reference vehicle speeds of 30 mph for rubber -tired vehicles and 50 mph for steel -wheel vehicles. Use the following relationship to calculate the adjustments for other speeds.
speed
Adjspeed (dB) = 20log(s eed )
p ref
Eq. 6-4
Variation with speed has been observed to be as low
as 15log( speed
speedref but unless specific speed data for vibration for a vehicle has been obtained, use Eq. 6-4.
• Vehicle Parameters — The most important factors for the vehicles are the suspension system, wheel condition, and wheel type. Most new heavy rail and light rail vehicles have relatively soft primary suspensions.
However, a stiff primary suspension (vertical resonance frequency greater than 15 Hz) can result in higher levels of ground -borne vibration than soft primary suspensions. Vehicles, for which the primary suspension consists of rubber or neoprene around the axle bearing, usually have a very stiff primary suspension with a vertical resonance frequency greater than 40 Hz or more.
Deteriorated wheel condition is another factor that increases vibration levels. It can be assumed that a new system has vehicles with wheels in good condition. When older vehicles are used on new track, it is important to consider the condition of the wheels, and it may be appropriate to include an adjustment for the wheel condition.
Resilient wheels will reduce vibration levels at frequencies greater than the effective resonance frequency of the wheel. When this resonance 4907
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frequency is relatively high, greater than 80 Hz, resilient wheels may only have a marginal effect on ground -borne vibration.
The adjustments in this category are not additive; apply the greatest applicable value only.
• Track Conditions — This category includes the type of rail (welded, jointed, or special trackwork), the track support system, and the condition of the rail. The base curves assume welded rail in good condition. Jointed rail causes higher vibration levels than welded rail and the increase depends on the condition of the joints.
Wheel impacts at special trackwork, such as frogs at crossovers, create much higher vibration forces than typical track conditions. Because of the higher vibration levels at special trackwork, crossovers are the principal areas of vibration impact on new systems. Methods of mitigating the vibration impact include modifying the track support system, installing low -impact frogs, or relocating the crossover. Special track support systems such as ballast mats, high -resilience track fasteners, resiliently supported ties, and floating slabs have all been shown to be effective in reducing vibration levels.
The condition of the running surface of the rails can strongly affect vibration levels. Factors such as corrugations, general wear, or mill scale on new track can cause vibration levels 5 to 15 dB higher than normal.
Mill scale will typically wear away after some time in service, but the track must be ground to remove corrugations or to reduce the roughness from wear.
Roadway surfaces in the rubber -tired vehicle base curve are assumed to be smooth. Rough washboard surfaces, bumps, or uneven expansion joints are the types of running surface defects that cause increased vibration levels over the smooth road condition.
The adjustments in this category are not additive; apply the greatest applicable value only. If there are adjustments for vehicle parameters and the track is worn or corrugated, only include one adjustment. 2b. Apply path adjustments to the base curve using Table 6-12 and the descriptions below to account for the project -specific path characteristics. 4908
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Table 6-I2 Path Adjustment Factors for Generalized Predictions of GB Vibration and Noise Path Factor
Adjustment to Propagation Curve
Comment
Resiliently
Supported
Ties
(Low - -10
Vibration
Track, LVT)
dB
Resiliently supported tie systems have been
found to provide very effective control of
low -frequency vibration.
Track Structure (not additive, apply greatest value only) Type of
Transit
Structure
Relative to at -grade tie & ballast:
Elevated structure
Open cut
-I0 dB
0 dB
In general, the heavier the structure, the
lower the vibration levels. Putting the track
in cut may reduce the vibration levels slightly.
Rock -based subways generate higher -
frequency vibration.
Relative to bored subway tunnel
Station
Cut and cover
Rock -based
in soil:
-5 dB
-3 dB
-I5 dB
Ground -borne Propagation Effects
Geologic
conditions that
promote
efficient
vibration
propagation
Efficient propagation in soil
+10 dB
Refer to the text for guidance on identifying
areas where efficient propagation is possible.
Propagation
in rock layer
Dist.
Adjust.
The positive adjustment accounts for the
lower attenuation of vibration in rock
compared to soil. It is generally more difficult
to excite vibrations in rock than in soil at the
source.
50 ft
100 ft
150 ft
200 ft
+2 dB
+4 dB
+6 dB
+9 dB
Coupling to
building
foundation
Wood -Frame Houses
1-2 Story Masonry
3-4 Story Masonry
Large Masonry on Piles
Large Masonry on Spread
Footings
Foundation in Rock
-5 dB
-7 dB
-I0 dB
-10 dB
-13 dB
0 dB
In general, the heavier the building
construction, the greater the coupling loss.
In addition to the comments in Table 6-12, use the following guidelines to select the appropriate adjustment factors.
• Track Structure — The weight and size of a transit structure affects the vibration radiated by that structure. In general, vibration levels are lower for heavier transit structures. Therefore, the vibration levels from a cut -and -cover concrete double -box subway can be assumed to be lower than the vibration from a lightweight concrete -lined bored tunnel.
The vibration from elevated structures is lower than from at -grade track because of the mass and damping of the structure and the extra distance that the vibration must travel before it reaches the receiver.
Elevated structures in AGT applications are sometimes designed to bear on building elements. This is a special case and may require detailed design considerations.
The adjustments in this category are not additive; apply the greatest applicable value only.
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• Ground -Borne Propagation Effects — Geologic Conditions — Although it is known that geologic conditions have a considerable effect on the vibration levels, it is rarely possible to develop more than a general understanding of the vibration propagation characteristics for a General Vibration Assessment. One of the challenges with identifying the cause of efficient propagation is the difficulty in determining whether higher than normal vibration levels are due to geologic conditions or due to special source conditions (e.g., rail corrugations or wheel flats).
Some geologic conditions are repeatedly associated with efficient propagation. Shallow bedrock, less than 30 ft below the surface, is likely to have efficient propagation. Soil type and stiffness are also important factors in determining propagation characteristics. In particular, stiff, clayey soils, consolidated sand, gravel, and glacial till can be associated with efficient vibration propagation. Investigation of soil boring records can be used to estimate depth to bedrock and the presence of problem soil conditions.
A conservative approach would be to use the I 0 -dB adjustment for efficient propagation for areas where efficient propagation is likely.
However, this adjustment can greatly overstate the potential for vibration impact where efficient propagation is not present and should be applied using good judgment. Review available geological data and any complaint history from existing transit lines and major construction sites near the transit corridor to identify areas where efficient propagation is possible. If there is reason to suspect efficient propagation conditions, conduct a Detailed Vibration Analysis during the engineering phase and include vibration propagation tests at the areas with potential for efficient propagation.
• Track Structure and Geologic Conditions — Examples
▪ Subway
For a subway, determine if the subway will be founded in bedrock.
Bedrock is considered to be hard rock. It is usually appropriate to consider soft siltstone and sandstone to be more like soil than hard rock. Whether a subway is founded in soil or rock can make a I5 - dB difference in the vibration levels.
When a subway structure is founded in rock, include the following Track Structure and Ground -borne Propagation Effects adjustments from Table 6-12:
— Type of Transit Structure adjustment: Rock -based — 15 dB — Geologic Conditions adjustment: Propagation in rock layer for the appropriate distance.
This adjustment increases with distance because vibration attenuates more slowly in rock than in the soil used as a basis for the reference curve.
• At -grade — When considering at -grade vibration sources, determine if the vibration propagation characteristics are typical or efficient. Efficient 4910
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vibration propagation results in vibration levels approximately I O dB higher than typical levels. This more than doubles the potential impact zone for ground -borne vibration.
• Ground -Borne Propagation Effects — Coupling to Building Foundation — Since annoyance from ground -borne vibration and noise is an indoor phenomenon, the effects of the building structure on the vibration must be considered. Wood -frame buildings, such as typical residential structures, are more easily excited by ground vibration than heavier buildings. In contrast, large masonry buildings with spread footings have a low response to ground vibration.
When a building foundation is directly on the rock layer, there is no coupling loss due to the weight and stiffness of the building. Use the standard coupling factors based on building type if there is at least a 10 - foot layer of soil between the building foundation and the rock layer. 2c. Apply receiver adjustments to the base curve using Table 6- 13 and the descriptions below to account for the project -specific receiver characteristics.
The data in Table 6-13 is applicable when the building structural features are known.
For more generic cases that do not have detailed information on individual buildings, use a conservative approach and apply the following adjustments to predict indoor vibration based on the outdoor vibration, instead of using the adjustments in Table 6-13:(43)(50)
• Light -weight, wood -frame construction I st floor: +3 dB • Light -weight, wood -frame construction 2nd and 3rd floors: +6 dB • Large buildings: 0 dB
• Small masonry buildings: +3 dB
Table 6-I3 Receiver Adjustment Factors for Generalized Predictions of GB Vibration and Noise Receiver
Factor
Adjustment to
Propagation Curve
Comment
Floor -to -floor
attenuation
I to 5 floors
above grade
5 to 10 floors
above grade
-2 dB/floor
- I dB/floor
This factor accounts for dispersion and attenuation
of the vibration energy as it propagates through a
building starting with the first suspended floor.'
Amplification
due to
resonances of
floors, walls,
and ceilings
+6 dB
The actual amplification will vary greatly depending
on the type of construction. The amplification is
lower near the wall/floor and wall/ceiling
intersections.
* Floor -to -floor attenuation adjustments for the first floor assume a basement. 4911
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In addition to the comments in Table 6- 13, use the following guidelines to select the appropriate adjustment factors. Note that receiver adjustments are additive. ■ Vibration generally reduces in level as it propagates through a building.
As indicated in Table 6-I 3, a I- to 2 -decibel attenuation per floor is typically appropriate.
• Resonances of the building structure, particularly the floors, will cause some amplification of the vibration. Consequently, for a wood -frame structure, the building -related adjustments nearly cancel out. Example:
All adjustments for the first floor assuming a basement are: -5 dB for the coupling loss; -2 dB for the propagation from the basement to the first floor; and +6 dB for the floor amplification. The total adjustment in this case is -I dB.
2d. Apply adjustments to the final adjusted curve using Table 6- I4 and the descriptions below to convert ground -borne vibration levels to ground -borne noise levels.
Table 6-I4 Conversion to Ground -borne Noise
Conversion to Ground -borne Noise
Peak frequency of ground vibration:
Use these adjustments to estimate the A -
Low frequency ( 60 Hz)
-20 dB
Estimate the levels of radiated noise using the average vibration amplitude of the room surfaces (floors, walls, and ceiling), and the total acoustical absorption in the room.
The un-weighted sound pressure level is approximately 5 dB(37)(43) less than the vibration velocity level when the velocity level is referenced to I x 10-6 inches/sec; but for a better estimate, it is necessary to consider general frequency ranges. Since ground -borne noise is A -weighted, the adjustments vary by frequency range, as described below. See Appendix B. I .4. I for more information on A -weighting.
To select the appropriate adjustment, classify the frequency characteristics according to the guidelines below.
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■ Low Frequency ( 60 Hz) — High -frequency characteristics can be assumed for the following conditions:
ci Subways with the transit structure founded in rock
• Subways, when there is very stiff, clayey soil
Step 3: Inventory of Vibration Impact
Take inventory of vibration -sensitive land uses with impact and determine if a Detailed Vibration Analysis is required.
Compare the projected vibration levels, including all appropriate adjustments in Section 6.4, Step 2, to the criteria to determine if impact from ground -borne vibration or noise is likely. Note that for any transit mode, variation in vibration levels under apparently similar conditions is not uncommon. In the General Vibration Assessment, it is preferable to make a conservative assessment of the impact and include buildings that may ultimately not be subject to impact.
The standard curves in Section 6.4, Step I, represent the upper range of vibration levels from well -maintained systems. Although actual levels fluctuate widely, it is rare that ground -borne vibration will exceed these curves by more than I or 2 dB unless there are extenuating circumstances such as wheel- or running -surface defects. However, because actual levels of ground -borne vibration will sometimes differ substantially from the projections, use the following guidelines to interpret vibration impact:
■ Projected vibration is below the impact threshold — Vibration impact is unlikely, and the environmental document should state this. • Projected ground -borne vibration is 0 to 5 dB greater than the impact threshold — There is a strong chance that actual ground -borne vibration levels will be below the impact threshold. The environmental document should report impact at these locations as exceeding the applicable threshold, present possible mitigation measures and costs, and commit to conducting more detailed studies to refine the vibration impact analysis during the engineering phase. During the Detailed Vibration Analysis, determine appropriate mitigation, if necessary. A site -specific Detailed Vibration Analysis may show that vibration impacts will not occur and control measures are not needed.
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■ Projected ground -borne vibration is 5 dB or greater than the impact threshold — Vibration impact is probable and Detailed Vibration Analysis must be conducted during the engineering phase to determine appropriate vibration control measures. The environmental document should report impact at these locations as exceeding the applicable threshold, present possible mitigation measures and costs, and commit to conducting more detailed studies to refine the vibration impact analysis during the engineering phase. During the Detailed Vibration Analysis, determine appropriate mitigation, if necessary. A site -specific, Detailed Vibration Analysis may show that very costly vibration mitigation must be incorporated into the project to eliminate the impacts.
FTA recommends the reporting of a vibration level as a single value and not as a range, as ranges tend to confuse the interpretation of impact.
Express the results of the General Vibration Assessment in terms of an inventory with the following components:
• Include all vibration -sensitive land uses as identified in the Vibration Screening Procedure.
• Organize the inventory according to the categories described in Table 6-8.
• Include information on potentially feasible mitigation measures to reduce vibration to acceptable levels based on the generalized reduction estimates provided in this section. To be considered feasible, the measure or combination of measures must provide at least a 5 -dB reduction of the vibration levels and be reasonable in terms of cost.
These potential mitigation measures are considered preliminary. Final vibration mitigation measures can only be specified after a Detailed Vibration Analysis has been done; see Section 6.5 for more information. Vibration control is frequency -dependent; therefore, specific recommendations of vibration control measures can only be made after evaluating the frequency characteristics of the vibration.
Example 6- I General Vibration Assessment — LRT
General Vibration Assessment for an LRT project
The hypothetical project is a LRT system that operates at 40 mph on at -grade, ballast and tie track with welded rail. The first floor of houses is at 125 ft from the LRT tracks and there is efficient propagation through the soil.
The houses are constructed with wood frames. The houses will be exposed to 260 train passbys per day.
Calculate the ground -borne vibration and assess for impact.
Select Base Curve for Ground Surface Vibration
Determine the appropriate base curve and the RMS velocity level (4).
According to Table 6-9, the Rapid Transit or Light Rail Vehicles curve is appropriate.
L„ = 65 VdB at 125 ft for this curve at 50 mph
Apply Adjustments
Apply the appropriate source adjustments using Table 6- I I. 4914
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40 Source Speed Adjustment = 20 log (50) = —1.9 dB
L„=65-1.9=63.1VdB
Apply the appropriate path adjustments using Table 6-12.
Efficient propagation = +10 dB
Coupling to building foundation (wood frame) = —5 dB
= 63.1 + 10 - 5 = 68.1 VdB
Apply the appropriate receiver adjustments using Table 6-I 3.
Amplification due to resonance of floor = +6 dB
First floor attenuation = —2 dB
L„ = 68.1+6-2 = 72.1 VdB
Assess for Impact
Because there are more than 70 events per day, this project is in the Frequent Events category (Table 6-2). For category 2 land uses (residences) with frequent events, the impact criteria is 72 VdB (Table 6-3). Therefore, according to the General Vibration Assessment, there is potential for impact and a Detailed Vibration Analysis should be completed.
6.5 Evaluate Impact: Detailed Vibration Analysis
Evaluate for impact using the Detailed Vibration Analysis procedure, if appropriate (Section 6. I).
The goal of the Detailed Vibration Analysis is to use all available tools to develop accurate projections of potential ground -borne vibration impact and when necessary, to design mitigation measures. A Detailed Vibration Analysis requires developing estimates of the frequency components of the vibration signal, usually in terms of I/3 -octave -band spectra. The analytical techniques for solving vibration problems are complex, and the technology continually advances. Therefore, the approach presented in this section focuses on the key steps for these analyses. The key elements of the Detailed Vibration Analysis procedure and recommended steps are described below.
The methods in this section generally assume a steel-wheel/rail system. The procedures could be adapted to bus systems. However, this is rarely necessary because vibration impact is very infrequent with rubber -tired transit.
In general, when situations arise that are not explicitly covered in the Detailed Vibration Analysis, professional judgment may be used to extend these methods to cover these unique cases, when appropriate. Appendix G provides information on developing and using non-standard modeling procedures.
Step I : Characterize Existing Vibration Conditions
Conduct measurements to survey and document the existing vibration conditions.
In contrast to noise impact analysis, the existing ambient vibration is not required to assess vibration impact in most cases; but, it is important to 4915
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document general background vibration in the project corridor. Because the existing environmental vibration is usually below human perception, a limited vibration survey is sufficient even for a Detailed Vibration Analysis.
It is particularly valuable to survey vibration conditions at sensitive locations for the following reasons:
• To obtain valuable information on the true sensitivity of the activity to external vibration and obtain a reference condition under which vibration is not problematic.
• To document that existing vibration levels are above or below the normal threshold of human perception for the existing condition. • To document levels of vibration created by existing rail lines. If vibration from an existing rail line is higher than the proposed train, there may not be impact even if the standard impact criteria are exceeded. • To use existing vibration sources to characterize propagation. Existing vibration sources such as freight trains, industrial processes, quarrying operations, or normal traffic can be used to characterize vibration propagation. Carefully designed and performed measurements may eliminate the need for more complex propagation tests. See Appendix G for information on using non-standard modeling procedures. • To identify the potential for efficient vibration propagation. If a measurement site has existing vibration approaching the range of human perception (e.g., the maximum vibration velocity levels are greater than about 65 VdB), then this site should be carefully evaluated for the possibility of efficient vibration propagation.
Conduct measurements to characterize existing vibration conditions. The goal of most ambient vibration measurements is to characterize the rms vertical vibration velocity level at the ground surface. In almost all cases, it is sufficient to measure only vertical vibration and ignore the transverse components of the vibration. Although transverse components(51) can transmit vibration energy into a building, the vertical component typically dominates.
I a. Choose Measurement Locations — Conduct outdoor and/or indoor measurements to characterize existing vibration conditions, as appropriate, for the project. Although ground -borne vibration is almost exclusively a problem inside buildings, it is generally recommended to perform measurements outdoors because equipment inside the building may cause more vibration than exterior sources. Additionally, the building structure and the resonances of the building can have strong effects on the vibration that are difficult to predict. It can also be important to measure and document those indoor sources of vibration. These indoor sources may cause vibration greater than that due to external sources like street traffic or aircraft overflights. When measuring (indoor) floor vibration, take measurements near the center of a floor span where the vibration amplitudes are the highest.
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I b. Measurement Considerations
■ Site selection — Selecting sites for an ambient vibration survey requires good judgment. Sites selected to characterize a transit corridor should be distributed along the entire project where potential for impacts have been identified and should be representative of the types of vibration environments found in the corridor. This would commonly include:
• Measurements in quiet, residential areas removed from major traffic arterials to characterize low -ambient vibration areas; • Measurements along major traffic arterials and highways or freeways to characterize high -ambient vibration areas;
• Measurements in any area with vibration -sensitive activities; and • Measurements at any major existing source of vibration such as railroad lines.
• Transducer placement — Place the transducers near the building setback line. For ambient measurements along railroad lines, it is recommended to include:
• Multiple sites at several distances from the rail line at each site, and • 4 to 10 train passbys for each test.
Because of the irregular schedule for freight trains and the low number of operations each day, it is often impractical to perform tests at more than two or three sites along the rail line or to measure more than two or three passbys at each site.
Rail type and condition strongly affect the vibration levels.
Consequently, it is important to inspect the track to locate any switches, bad rail joints, corrugations, or other factors that could be responsible for higher than normal vibration levels. Locations with these kinds of irregularities should be represented in addition to locations with rail in better condition.
• Transducer mounting methods — The way a transducer is mounted can affect the measured levels of ground -borne vibration. ▪ Straightforward methods of mounting transducers on the ground surface or on pavement are adequate for vertical vibration measurements for the frequencies of concern for ground -borne vibration (less than about 200 Hz).
• Quick -drying epoxy, clay, or beeswax can be used to mount transducers to smooth paved surfaces or metal stakes driven into the ground.
▪ Rough concrete or rock surfaces require special mountings. One approach is to use a liberal base of epoxy to attach small aluminum blocks to the surface, and then mount the transducers on the aluminum blocks.
• When in doubt, review the specific transducer documentation and discuss additional mounting guidance with the transducer manufacturer.
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I c. Existing Vibration Characterization — The appropriate methods of characterizing ambient vibration are dependent on the type of information required for the analysis. Consider the following when characterizing the existing vibration:
• Ambient vibration — Ambient vibration is usually characterized with a continuous 10- to 30 -minute measurement of vibration. The rms velocity level of the vibration velocity level over the measurement period provides an indication of the average vibration energy. The rms velocity level over the measurement period is typically equivalent to a long averaging time rms level.
• Specific events — Characterize specific events such as train passbys by the rms level over the time that the train passes by. If the locomotives produce vibration levels more than 5 dB higher than the passenger or freight cars, obtain a separate rms level for the locomotives. The locomotives can usually be characterized by the Lmax during the train passby. The rms averaging time or time constant should be I second when determining Lmax. In some cases, it may be adequate to characterize the train passby using Lmax, which is simpler to obtain than the rms averaged over the entire train passby.
• Spectral analysis — Perform a spectral analysis of vibration propagation data. For example, if vibration transmission of the ground is suspected of having particular frequency characteristics, use I /3 -octave band charts to describe vibration behavior. Narrowband spectra also can be valuable, particularly for identifying discrete frequency components and designing specific mitigation measures.
Note that it is preferred to characterize existing vibration in terms of the rms velocity level instead of the peak PPV, which is commonly used to monitor construction vibration. As discussed in Section 5.1, rms velocity is considered more appropriate than PPV for describing human response to building vibration.
Step 2: Estimate Vibration Impact
Estimate ground -borne vibration and noise at sites where significant impact is probable and assess for impact.
Predicting ground -borne vibration associated with a transportation project continues to be a developing field. Because ground -borne vibration is a complex phenomenon that is difficult to model and predict accurately, most projection procedures that have been used for transit projects rely on empirical data.
The procedure described in this section is based on site -specific tests of vibration propagation. This procedure was developed under a FTA-funded research contract(52) and is recommended for detailed evaluations of ground - borne vibration. Other approaches to a prediction procedure, such as finite element methods, can be used. See Appendix G for information on using non- standard modeling procedures.
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Overview of Prediction Procedure — This procedure was developed to allow the use of data collected in one location to accurately predict vibration levels in another site where the geologic conditions may be completely different.
The procedure is based on transfer mobility. Transfer mobility is the complex velocity response produced by a point force as a function of frequency. It represents the relationship between a vibration source that excites the ground and the resulting vibration of the ground surface. It is a function of both frequency and distance from the source. The analyses in this manual focus on transfer mobility magnitude, which is the magnitude for the velocity relative to the force without reference to phase. The transfer mobility level is the level in decibels relative to I E-6 in/lb-s.
The transfer mobility measured at an existing transit system is used to normalize ground -borne vibration data and remove the effects of geology. The normalized vibration is referred to as the force density. Force density is the force per root distance along the track in Ib/ft"2. The force density can be combined with transfer mobility measurements at vibration -sensitive sites along a new project to develop projections of future ground -borne vibration.
The transfer mobility between two points completely defines the composite vibration propagation characteristics between the two points. In most practical cases, receivers are close enough to the train tracks that the vibration cannot be considered as originating from a single point. Therefore, the vibration source must be modeled as a line -source. Consequently, the point transfer mobility must be modified to account for a line -source. The subsequent line -source transfer mobility is given in units of decibels relative to I e-6 in/s/Ib/sgrt(ft).
The prediction procedure considers ground -borne vibration to be divided into several basic components described below and shown in Figure 6-5. • Excitation Force (Force Density) — The vibration energy is created by oscillatory and impulsive forces. Steel wheels rolling on smooth steel rails create random oscillatory forces. When a wheel encounters a discontinuity such as a rail joint, an impulsive force is created. The force excites the transit structure, such as the subway tunnel or the ballast for at -grade track.
In the prediction method, the combination of the actual force generated at the wheel/rail interface and the vibration of the transit structure are usually combined into an equivalent force density level. The force density level is the level in decibels of the force density relative to I Ib/ft1/2 and describes the force that excites the soil/rock surrounding the transit structure.
• Vibration Propagation (Transfer Mobility) — The vibration of the transit structure causes vibration waves in the soil that propagate away from the transit structure. The vibration energy can propagate through the soil or rock in a variety of wave forms. All ground vibration includes shear and compression waves. Rayleigh waves (49) are also created and propagate along the ground surface. These Rayleigh waves can be a 4919
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major carrier of vibration energy. The mathematical modeling of vibration is complicated when there are soil strata with different elastic properties, which is common. As indicated in Figure 6-5, the propagation through the soil/rock is modeled using the transfer mobility, which is usually determined experimentally.
The combination of the force density level and the transfer mobility is used to predict the ground- surface vibration. This is the major difference from the General Vibration Assessment, which generalizes estimates of the ground -borne vibration.
• Building Vibration — When the ground vibration excites a building foundation, it sets the building into vibratory motion and vibration waves propagate throughout the building structure. The interaction between the ground and the foundation causes some reduction in vibration levels. The amount of reduction is dependent on the mass and stiffness of the foundation. The more massive the foundation, the lower the response to ground vibration. As the vibration waves propagate through the building, they can create vibration that can be felt and cause windows and household items to rattle.
• Audible Noise — In addition to vibration that can be felt, the vibration of room surfaces radiates low -frequency sound that may be audible. The sound level is affected by the amount of acoustical absorption in the receiver room.
Ground surface
vibration
Vibration of
floors & walls,
possible feelable
vibration
Audible ground -
borne noise
Oscillatory or
impulsive force
Track fixation
4 Track support
Track structure
Propagation through
soilirock to soil surface
and building foundations
Building foundation
Propagation through
building structure
Radiation of sound by
vibrating room surfaces
Acoustical absorption
in room
Excitation Force
(Force Density)
Vibration Propagation
(Transfer Mobility)
Building Vibration
Audible Noise
Figure 6-5 Ground -Borne Vibration and Noise Model
A fundamental assumption of the prediction approach outlined in this section is that the force density, transfer mobility, and the building coupling to the ground are all independent factors. The following equations are the basis for the 4920
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prediction procedure, where all of the quantities are one-third octave band spectral levels in decibels with consistent reference values:
where:
Lv = FDL + LSTM + Cbuild
LA = Lv + Krad + KA-wt
Lv
FDL
LSTM
Cbuild
LA
Krad
KA-wt
Eq. 6-5
Eq. 6-6
= rms vibration velocity level in VdB
= force density level in dB for a line vibration source such as a train
= line -source transfer mobility level in dB from the tracks to the sensitive site
= adjustments to account for ground -building foundation interaction and attenuation of vibration amplitudes as vibration propagates through buildings
= A -weighted sound level
= adjustment to account for conversion from vibration to sound pressure level including accounting for the amount of acoustical absorption inside the room. A value of -5 dB can be used for Krad for typical residential rooms when the decibel reference value for l—, is I micro in/sec (37)(50)
= A -weighting adjustment at the I/3 -octave band center frequency All of the quantities given above are functions of frequency, and the standard approach is to develop projections on a I/3 -octave band basis using the average values for each I /3 -octave band. The end results of the analysis are the I/3 - octave band spectra of the ground -borne vibration and the ground -borne noise.
The spectra are then compared to the vibration criteria for the Detailed Vibration Analysis. The A -weighted ground -borne noise level can be calculated from the vibration spectrum and compared to the criteria. This more detailed approach differs from the General Vibration Assessment, where the overall vibration velocity level and A -weighted sound level are predicted without any consideration of the particular frequency characteristics of the propagation path.
The key steps in obtaining quantities for Eq. 6-5 and Eq. 6-6 are presented in the following steps and include:
Step 2a. Estimate force density
Step 2b. Measure the point -source transfer mobility
Step 2c. Estimate line -source transfer mobility
Step 2d. Project ground -borne vibration and ground -borne noise 2a. Estimate Force Density — The estimate of force density can be based on previous measurements or a special test program can be designed to measure the force density at an existing facility.
If no suitable measurements are available, conduct testing at a transit facility with equipment similar to the planned vehicles. Adjustments for factors such as train speed, track support system, and vehicle suspension may be needed to match the force density to the conditions at a specific site. Review the report 4921
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"State -of- the -Art Review: Prediction and Control of Ground -Borne Noise and Vibration from Rail Transit Trains" (41) for examples of appropriate adjustments.
Force density is not a quantity that can be measured directly; it must be inferred from measurements of transfer mobility and train vibration at the same site. To derive force density, the best results are achieved by deriving line -source transfer mobility from a line of impacts. The standard approach is to average the force density from measurements at three or more positions at one site. If feasible, it is recommended to take measurements at more than one site and at multiple speeds.
If no suitable measurements are available, see Steps 2b and 2c for guidelines on obtaining line -source transfer mobility.
The force density for each I/3 -octave band is as follows:
FDL = L„ — LSTM Eq. 6-7
where:
FDL
L„
LSTM
= force density level in dB
= measured train ground -borne vibration
level in VdB
= line -source transfer mobility level in dB
Figure 6-6 shows example trackbed force densities in decibels relative to I lb/(ft)1/2. These force densities were developed from measurements of vibration from heavy and LRT vehicles and represent an incoherent line of vibration force equal to the length of transit trains. This figure provides a comparison of the vibration forces from heavy commuter trains and LRT vehicles with different types of primary suspensions, illustrating the range of vibration forces commonly experienced in a transit system. A force density of a vehicle includes the characteristics of its track support system at the measurement site. Adjustments must be applied to the force density to account for differences between the facility where the force density was measured and the new system being analyzed.
Figure 6-7 shows typical force densities for rail transit vehicles at 40 mph on ballast and tie tracks, which are approximately within the tolerances shown in Figure 6-6. The force densities should be applied very carefully for other track types and speeds. The embedded tracks, although considerably stiffer than ballast and tie tracks, are expected to show similar force density levels.(53) The curves in Figure 6-7 should also be applied with caution for newer generations of light rail vehicles as well as vehicles that utilize direct fixation tracks. The preferred approach for vibration predictions would be to perform force density measurements at a system with vehicles and operations that are similar to those of the future project.
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Force Density, dB re 1 lb/(ft)112
7-
IM
Commuter Rail Range
Commuter Rail Average
Light Rail Range
---- Light Rail Average
1/3 Octave Band Center Frequency, Hz
I I I
I-----`----4-----I-----I
125
1 Figure 6-6 Typical Force Densities for Rail Transit Vehicles, 40 mph 250
60 —
P.! 50
Rail Average
B&T Tracks
Rail Max for
Tracks
Rail Min for
Tracks
Light
for
V =
—Light
B&T
Light
40 _
—
—
B&T
''.------ \
.'
----------\_.„..____
:orce D
I"
5 8
16 31.5 63
113 Octave Band Frequency, Hz
125
Figure 6-7 Typical Force Densities for LRT Vehicles, 40 mph 250
2b. Measure Point -Source Transfer Mobility — Using the appropriate instrumentation, measure point -source transfer mobility for sources with short lengths, such as buses or single car vehicles or columns supporting elevated structures. For longer vehicles, see Section 2c for a discussion of measuring line - source transfer mobilities.
The test procedure to measure point -source transfer mobility consists of impacting the ground by dropping a heavy weight and measuring the force into the ground and the response at several distances from the impact. Other excitation sources may include swept sine, sine -dwell, random vibration, and maximum length sequence. The goal of the test is to create vibration pulses that 4923
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travel from the source to the receiver using the same path that will be taken by the transit system vibration.
Figure 6-8 illustrates the field procedure for measuring both at -grade and subway testing of transfer mobility. A weight is dropped from a height of 3 to 4 ft onto a force transducer. The responses of the force and vibration transducers are recorded on a multichannel recorder for later analysis in the laboratory. An alternative approach is to set up the analysis equipment in the field and capture the signals directly. This complicates the field testing, but eliminates the laboratory analysis of recorded data.
liDropped Weight
Load Cell
At -Grade Testing
Bore hole to
depth of
subway
Impact
Load Cell
Subway Testing
a Accelerometers
Figure 6-8 Test Configuration for Measuring Transfer Mobility When the procedure is applied to subways, the force must be located at the approximate depth of the subway. This is done by drilling a bore hole and locating the force transducer at the bottom of the hole. The tests are usually performed while the bore holes are drilled to allow for the use of the soil - sampling equipment on the drill rig for the transfer mobility testing. The force transducer is attached to the bottom of the drill string and lowered to the bottom of the hole. A standard soil sampling hammer is used to excite the ground; typically, a I 40 -pound weight is dropped I8 inches onto a collar that is attached to the drill string. The force transducer must be capable of operating under water if the water table is near the surface or a slurry drilling process is used.
Standard signal -processing techniques are used to determine the transfer function (frequency response function) between the exciting force and the resultant ground -borne vibration. Numerical regression methods are used to combine a number of two -point transfer functions into a smooth point -source transfer mobility level that represents the average vibration propagation characteristics of a site as a function of both distance from the source and 4924
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frequency. The transfer mobility level is usually expressed in terms of a group of I/3 -octave band transfer mobility levels. Figure 6-9 is an example of point - source transfer mobility levels from a series of tests at the Transportation Technology Center in Pueblo, Colorado.(50)(54)(55)(56)(57) 20 10
CO
13 ▪ p
J
a� -10
-2°
▪ -30
f
y�,.1..'�.- -Y- +tip I!
' II < I
• ...-.• _ .� 1'N... eta 1 'r
J __L____1__ __ • awl, __*I ``L____1 -L_.._wr--
s`
•
'
.
','' *. ; I' 1 .:200 f1, ..Ire -.I150 150 ft.
' 300 ft \ - - *...
J
r ----s----7
25 ft
50 ft
L
-. 100ft
J
8 16 31.5 63
1/3 Octave Band Center Frequency
125 250
Figure_6-9 Example of Point -Source Transfer Mobility
Instrumentation
Performing a transfer mobility test requires specialized equipment, which is generally available from commercial sources. Typical instrumentation for field- testing and laboratory analysis of transfer mobility is shown in Figure 6-10.
A load cell can be used as the force transducer. The force transducer should be capable of impact loads of 5,000 to 50,000 pounds depending on the hammer used for the impact. For borehole testing, the load cell must be hermetically sealed and capable of being used at the bottom of a 30- to I 00 -foot -deep hole partially filled with water.
Either accelerometers or geophones can be used as the vibration transducers.
Geophones should be carefully mounted so that they are vertical. The requirement is that the transducers with the associated amplifiers be capable of accurately measuring levels of 0.0001 in/sec at 40 Hz and have a flat frequency response from 6 Hz to 400 Hz. Data should be acquired with a digital acquisition system with a flat frequency response over the range of 6 to 400 Hz. 4925
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Field Equipment
Dropped Weight
or
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Force Transducer
Accelerometers
Signal Conditioning
and
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Figure 6-10 Equipment Required for Field Testing and Laboratory Analysis A narrowband spectrum analyzer or signal -processing software can be used to calculate the transfer function and coherence between the force and vibration data. The analyzer must be capable of capturing impulses from at least two channels to calculate the frequency spectrum of the transfer function between the force and vibration channels. All transfer functions should include the average of at least 20 impulses. Time averaging of the impulses will provide substantial signal enhancement, which is usually required to accurately characterize the transfer function. Signal enhancement is particularly important when the vibration transducer is more than 100 ft from the impact.
Alternative methods of determining transfer mobility may be used, provided that these techniques have been demonstrated to provide the same results as the conventional weight -drop method over the frequency range of 6 Hz to 400 Hz. See Appendix G for information on developing and using non-standard procedures. These methods may include using other impulse -response measurement systems involving the use of shakers or electro-mechanical actuators, stimuli such as sweeps or maximum length sequences (MLS), and various signal processing techniques. A forthcoming ANSI Standard will describe in detail the procedures, methodologies, and reporting requirements for performing ground -borne vibration propagation measurements.
The transfer function can be calculated with either a spectrum analyzer or signal -processing software. Note that transfer functions should include the average of at least 20 impulses. Specialized multi -channel spectrum analyzers have built-in capabilities for computing transfer functions and are computationally efficient. However, signal -processing software can offer more 4926
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flexibility in analyzing data signals and allows the use of different digital signal processing methods. Typical measurement programs involve acquisition of data in the field and later processing of the information in a laboratory. However, recent advances in instrumentation and signal -processing software allow data to be collected and analyzed while in the field.
2c. Estimate Line -Source Transfer Mobility — Estimate line -source transfer mobility for long sources such as multi -car trains. Line -source transfer mobilities are used to normalize measured vibration velocity levels from train passbys and to obtain force density. Two different approaches can be used to develop estimates of line -source transfer mobility. The first consists of using lines of transducers and the second consists of a line of impact positions.
Option A: Lines of Transducers — Develop line -source transfer mobility curves from tests using one or more lines of transducers as shown in Figure 6- I I and described below.
Narrowband Transfer Mobility
1/3 Octave Band Transfer Mobility
(one spectrum for each distance at each site)
Best -fit Curve of Transfer Mobility
as a Function of Distance
(one for each 1/3 octave band)
Line -Source Transfer Mobility
(estimated using numerical integration
of point source transfer mobility)
2 C �
Frequency
Frequency
Distance
47"Line Source
Point -- —
Source
Distance
Figure 6-1 I Analysis of Transfer Mobility
Ai. Obtain the narrowband transfer function between source and receiver at each measurement position. There should be a minimum of four distances in any test line. Because of the possibility of local variations in propagation characteristics, two or more lines should be used to characterize a site if possible. A total of I 0 to 20 transducer positions are often used to characterize a site.
Aii. Calculate the equivalent I/3 -octave band transfer functions, generally between 6 and 400 Hz. This reduces each spectrum to 15 numbers. As shown in Figure 6 -I I, the I/3 -octave band spectrum is much smoother than the narrowband spectrum.
Aiii. Calculate a best -fit curve of transfer mobility as a function of distance for each I /3 -octave band. When analyzing a specific site, the best -fit curve will be 4927
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based on I 0 to 20 points. Up to several hundred points could be used to determine average best -fit curves for a number of sites.
Aiv. Apply the best -fit curve to the vibration sources. The I /3 -octave band best -fit curves can be directly applied to point vibration sources. Buses can usually be considered point -sources, as can columns supporting elevated structures. However, for a line vibration source such as a train, numerical integration must be used to calculate the equivalent line -source transfer mobility. The numerical integration procedures are detailed in the TRB publication: "A Prediction Procedure for Rail Transportation Ground -Borne Noise and Vibration."(50)
Option B: Line of Impulses — This second procedure for estimating line - source transfer mobility is best for detailed assessment of specific vibration paths or specific buildings and is a more direct approach.
Bi. Measure multiple point -source transfer mobilities according to the procedures in Step 2b above. The vibration transducers are placed at specific points of interest and a line of impacts is used. For example, a I 50 -foot train might be represented by a line of I I impact positions along the track centerline at 15 -foot intervals (Figure 6-12).
Bii. Sum the point -source results using Simpson's rulexiii for numerical integration to calculate the line -source transfer mobility.
Figure 6-13 shows an example of line -source transfer mobilities that were derived from the point -source transfer mobilities shown in Figure 6-9. r
$C'
,yxm
Figure 6-I2 Schematic of Transfer Mobility Measurements Using a Line of Impacts xiii Simpson's rule is a method for approximating integrals. 4928
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40 -a 30
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16 31,5 63
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ft
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125 250
Figure 6-13 Example of Line -source Transfer Mobility
2d. Project Ground -Borne Vibration and Noise — Combine force density and line -source transfer mobility to project ground -borne vibration. Then, apply adjustment factors to estimate the building response to the ground -borne vibration and to estimate the A -weighted sound level inside buildings.
The propagation of vibration from the building foundation to the receiver room is very complex and dependent on the specific design of the building. Detailed evaluation of the vibration propagation would require extensive use of numerical procedures such as the finite element method. Such a detailed evaluation is generally not practical for individual buildings considered in this manual. If the detailed features of the individual buildings are available, the recommended procedure is to estimate the propagation of vibration through a building and the radiation of sound by vibrating building surfaces using simple empirical or theoretical models. The recommended procedures are outlined in the Handbook of Urban Rail Noise and Vibration Control.(44) The approach consists of adding the following adjustments to the I /3 -octave band spectrum of the projected ground -borne vibration:
• Building response or coupling loss — This adjustment represents the change in the incident ground -borne vibration due to the presence of the building foundation. The adjustments described in the handbook (44) are shown in Figure 6- I4. Note that the correction is zero when estimating basement floor vibration or vibration of at -grade slabs.
Measured values may be used in place of these generic adjustments. • Transmission through the building — The vibration amplitude typically decreases as the vibration energy propagates from the foundation through the remainder of the building. The general assumption is that vibration attenuates by I to 2 dB for each floor. • Floor resonances — Vibration amplitudes will be amplified because of resonances of the floor/ceiling systems. For a typical wood -frame 4929
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residential structure, the fundamental resonance is usually in the 15 to 20 Hz range. Reinforced -concrete slab floors in modern buildings will have fundamental resonance frequencies in the 20 to 30 Hz range. An amplification resulting in a gain of approximately 6 dB should be used in the frequency range of the fundamental resonance.
• Floor vibration and ground -borne noise — The projected floor vibration is used to estimate the levels of ground -borne noise. The primary factors affecting noise level are the average vibration level of the room surfaces and the amount of acoustical absorption within the room. The radiation adjustment is -5 dB for typical rooms, (37) (50) which gives:
where:
LA LIT +KA-wt-5
LA
L„
KA-wt
Eq. 6-8
= A -weighted sound level in a I /3 -octave band
= rms vibration velocity level in that band
= A -weighting adjustment at the I /3 -octave band center frequency
The A -weighted levels in the I /3 -octave bands are combined to produce the overall A -weighted sound level.
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125
Figure 6-14 Foundation Response for Various Types of Buildings 250
Where detailed information on the structural features of individual buildings are unavailable and there are no site -specific data on outdoor to indoor propagation characteristics, the preferred approach is to apply a combined factor for the foundation response and the gain from floor resonances. Empirical data based on the TCRP D-12 Project from 34 measurement sites across 5 cities in North FEDERAL TRANSIT ADMINISTRATION 164
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America and other studies suggest that the average change in vibration from outdoor to indoor was 0 dB across all I/3 -octave bands with a standard deviation of approximately 5 to 6 dB in the 3 I.5 to 63 Hz frequency.(43)(48) Therefore, the recommended approach for predicting indoor vibration based on outdoor data is to use an adjustment of +3 to +6 dB for light -weight, wood - frame construction and use an adjustment of 0 dB for heavier buildings.
However, for buildings with high -vibration sensitivity or where there is concern regarding interference with vibration -sensitive equipment, it is advisable to measure the outdoor -indoor response of the building, using the process described in Section 2b or 2c, to determine the actual response of the foundation and building to vibration.
Step 3: Assess Vibration Impact
Take inventory of vibration -sensitive land uses with impact.
Assess vibration impact at each receiver of interest using the impact criteria in Section 6.3. Note that ground -borne vibration and noise levels that exceeded criteria in the General Vibration Assessment may not cause impact according to the more detailed procedures of the Detailed Vibration Analysis; in which case, mitigation is not required. But if projected levels still exceed the criteria, evaluate vibration mitigation measures using the spectra provided by the Detailed Vibration Analysis.
Step 4: Determine Vibration Mitigation Measures
Select practical vibration control measures that will be effective at the dominant vibration frequencies and compatible with the given transit structure and track support system.
The purpose of vibration mitigation is to minimize the adverse effects that the project ground -borne vibration and ground -borne noise will have on sensitive land uses. Because ground -borne vibration is not as common a problem as environmental noise, the mitigation approaches have not been as well defined. In some cases it may be necessary to develop innovative approaches to control the impact. See Appendix G for information on using non-standard methods.
Standard vibration control measures for rail transit systems are discussed in this step. Note that vibration control measures for rail transit systems are not always effective for freight trains.(xi') Bus systems rarely cause vibration impact, but if impact occurs, roadway roughness or unevenness caused by bumps, pot holes, expansion joints, or driveway transitions are usually the causes.
Smoothing the roadway surface is typically the recommended course of action.(xv)
xiv The heavy axle loads associated with freight rail are outside the range of applicable design parameters for vibration reduction on lighter rail transit systems. Plans to relocate existing railroad tracks closer to vibration -sensitive sites in order to accommodate a new rail transit line in the ROW must be carefully considered because it may not be possible to mitigate the increased vibration impact from freight trains.
xv In cases where a rubber -tired system runs inside a building, such as an airport people mover, vibration control may involve additional measures. Loading and unloading of guideway support beams may generate dynamic forces that transmit into the building structure. Special guideway support systems may be required, similar to the discussion below regarding floating slabs. 4931
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Vibration reduction measures incur additional costs to a system. Some of the same treatments for noise mitigation can be considered for vibration mitigation.
Costs for noise control measures are documented in a report from the Transit Cooperative Research Program (TCRP).(31) Where applicable to vibration reduction, costs for noise abatement methods from that report are given in the following sections. These costs reflect the noise mitigation costs as of 1997 (unless otherwise noted), and should only be used as representative estimates when considering noise mitigation options. Current noise mitigation costs should be researched before decisions on noise mitigation options are finalized, and then they should be documented according to Section 8.
Mitigation of vibration impacts may involve treatments at the source, along the source -to -receiver propagation path, or at the receiver.
I a. Evaluate Source Treatments — The most effective vibration mitigation treatments are applied at the vibration source. This is the preferred approach to mitigation when possible. Possible source treatments include:
■ Preventative Maintenance — Effective maintenance programs are essential for controlling ground -borne vibration. Key vibration points are discussed below; see Section 4.5, Step 7 for more detailed information on the benefits of effective maintenance programs on controlling transit noise and vibration. While these are not mitigation measures in the traditional sense, and should not be included as mitigation in an environmental document, they can help to keep both noise and vibration levels at a "like -new" level or reduce both in systems with deferred maintenance.
Rail grinding is a particularly important practice for vibration mitigation for rail that develops corrugations. The TCRP report notes that periodic rail grinding results in a net savings per year on wheel and rail wear. Most transit systems contract out rail grinding, although some of the larger systems make the investment and do their own grinding. As mentioned in Section 4.5, Step 7, the typical rail grinding cost would be $ I000 to $7000 per grinding pass mile, with an additional investment of approximately $ I million for the equipment for a larger transit system to do its own grinding. ▪ Dramatic vibration reduction results can be achieved by removing wheel flats through wheel truing. As mentioned in Section 4.5, Step 7, a wheel truing machine costs approximately $ I million, including associated maintenance, materials, and labor costs.
The TCRP report figures a system with 700 vehicles would incur a yearly cost of $300,000 to $400,000 for a wheel truing program. • Profile grinding of the rail head in combination with a wheel truing program may be the most practical approach to controlling and reducing vibration and noise where such practices are not normally conducted. Profiles should be defined during the design phase and should be in place when system opens.(32) The cost of 4932
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wheel and rail profile matching may be incorporated in the new vehicle and new rail costs.
Rough wheels or rails can increase vibration levels by as much as 20 dB in extreme cases, negating the effects of even the most effective vibration control measures. Yet, it is rare that vibration control measures (such as those discussed below) will provide more than 15 to 20 dB attenuation. When there are ground -borne vibration impacts with existing transit equipment, the best vibration control measure often is to implement new or improved maintenance procedures. Grinding rough or corrugated rail and wheel truing to eliminate wheel flats and restore the wheel contour may provide considerable vibration reduction. Regular maintenance may replace the need to modify the existing track system, such as through adding floating slabs.
• Planning and Design of Special Trackwork — A large percentage of the vibration impact from a new transit facility is often caused by wheel impacts at special trackwork for turnouts and crossovers. When feasible, the most effective vibration control measure is to relocate the special trackwork to a less vibration -sensitive area. This may require adjusting the location by several hundred feet provided it will not have an adverse impact on the operation plan for the system. Careful review of crossover and turnout locations during the project development phase is an important step to minimizing potential for vibration impact.
Another approach is to use special devices (frogs) at turnouts and crossovers that incorporate mechanisms to close the gaps between running rails. Frogs with spring -loaded mechanisms and frogs with movable points can substantially reduce vibration levels near crossovers.
According to the TCRP report, a spring frog costs about $ 12,000, twice the cost of a standard frog. A movable point frog involves elaborate signal and control circuitry resulting in higher costs at approximately $200,000.
• Vehicle Specifications — The ideal rail vehicle with respect to minimizing ground -borne vibration should have the following characteristics:
• Low, unsprung weight
• Soft primary suspension
• A minimum of metal -to -metal contact between moving parts of the truck
▪ Smooth wheels that are perfectly round
A limit for the vertical resonance frequency of the primary suspension should be included in the specifications for any new vehicle. A vertical resonance frequency of 12 Hz or less is sufficient to control the levels of ground -borne vibration, although some have recommended the vertical resonance frequency be less than 8 Hz.
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• Special Track Support Systems — When the vibration assessment indicates that vibration levels will be excessive, the track support system is typically modified to reduce the vibration levels.
Floating slabs, resiliently supported ties, high -resilience fasteners, and ballast mats can be used to reduce the levels of ground -borne vibration.
To be effective, all of these measures must be optimized for the frequency spectrum of the vibration. Most of these relatively standard procedures have been successfully used on several subway projects.
Applications on at -grade and elevated track are less common. This is because vibration impact is less common for at -grade and elevated track. Note that the cost of these types of vibration control measures is a higher percentage of the overall construction costs for at -grade and elevated track, and exposure to the elements can require substantial design modifications.
Each major vibration control measure for track support is discussed below. Costs for these treatments are not covered by the TCRP report, but are given as estimates based on transit agency experience.
Resilient fasteners — Resilient fasteners are used to fasten the rail to concrete track slabs. Standard resilient fasteners are very stiff in the vertical direction, usually in the range of 200,000 lb/in, and do provide some vibration reduction compared to the rigid fastening systems used on older systems (e.g., wood half - ties embedded in concrete).
Special fasteners with vertical stiffness in the range of 30,000 lb/in may reduce vibration by as much as 5 to I O dB at frequencies above 30 to 40 Hz. These premium fasteners vary in cost and can be priced competitively when purchased in large quantities.
Ballast mats — A ballast mat consists of a rubber or other type of elastomer pad that is placed under the ballast. In general, the mat must be placed on a concrete pad to be effective. They will not be as effective if placed directly on the soil or the sub - ballast. Consequently, most ballast mat applications are in subway or elevated structures.
Ballast mats can provide 8 to 12 dB attenuation at frequencies above 25 to 30 Hz.(58) Ballast mats are often a good retrofit measure for existing tie -and -ballast track where there is vibration impact. Installed ballast mats cost approximately $ 180 per track -foot.
Undertie pads — Undertie pads (resiliently supported
concrete ties) consist of a rubber pad mounted on the bottom of a concrete tie directly on the ballast. The pads provide vibration isolation at frequencies above 25 Hz and are easy to 4934
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install or retrofit. Installed undertie pads cost approximately $260 per track -foot.
Resiliently supported ties — The resiliently supported tie system consists of concrete ties supported by rubber pads resting on top of a slab track or subway invert. The rails are fastened directly to the concrete ties using standard rail clips.
Resiliently supported ties provide vibration reduction in between 15 to 40 Hz, which is particularly appropriate for transit systems with vibration impact in the 20 to 30 Hz range.
A resiliently supported tie system costs approximately $400 per track -foot.
Floating slabs — Floating slabs can be very effective at controlling ground -borne vibration and noise and consist of a concrete slab supported on resilient elements such as rubber or a similar elastomer. Floating slabs are effective at frequencies greater than their single -degree -of -freedom vertical resonance frequency.
Floating slabs are among the most expensive vibration control treatments. A typical double -tie floating slab system costs approximately 4 times the cost of ballast and tie per track foot.
Examples of floating slabs include:
— Floating slabs used in Washington, DC; Atlanta, GA; and Boston, MA, were all designed to have a vertical
resonance in the 14 to 17 Hz range.
— A special system referred to as the double -tie system was first used in Toronto. It consists of 5 -foot -long slabs with four or more rubber pads under each slab.
This system was designed with a resonance frequency in
the 12 to 16 Hz rang3.
— Another special floating slab was used in San Francisco's Bay Area Rapid Transit (BART) system. It uses a
discontinuous precast concrete double -tie system with
a resonance frequency in the 5 to I 0 Hz frequency
range.
• Tire -derived aggregate (TDA) — TDA (shredded tires) consists of a layer of tire shreds wrapped in geotech fabric placed underneath the ballast on hard packed ground. This is a new, low- cost option that can provide reduction in vibration levels at frequencies above 25 Hz. This mitigation measure has proven to be effective for the Denver Regional Transportation District (RTD) light rail system as well as the Santa Clara Valley Transportation Authority (VTA) light rail system,(59) but the effective life of TDA has not been determined. Installed TDA costs approximately $260 per track -foot.
• Other treatments — Changing any feature of the track support system can change the levels of ground -borne vibration. Approaches 4935
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such as using heavier rail, thicker ballast, or heavier ties can be expected to reduce the vibration levels. There also is some indication that vibration levels are lower with wood ties compared to concrete ties. But there is little confirmation that any of these approaches will make a substantial change in the vibration levels. • Operational Changes — The most effective operational change is to reduce the vehicle speed. Reducing the train speed by a factor of two will reduce vibration levels approximately 6 dB. Other operational changes include:
Use of equipment that generates the lowest vibration levels during the nighttime hours when people are most sensitive to vibration and noise.
Adjusting nighttime schedules to minimize movements in the most sensitive hours.
While there are tangible mitigation benefits from speed reductions and limits on operations during the most sensitive time periods, FTA does not generally accept speed reduction as a vibration mitigation measure for two important reasons: (I) speed reduction is unenforceable and negated if vehicle operators do not adhere to established policies, and (2) it is contrary to the purpose of the transit investment by FTA, which is to move as many people as possible as efficiently and safely as possible. FTA does not recommend limits on operations as a way to reduce vibration impacts.
I b. Evaluate Path Treatments — When vibration mitigation treatments cannot be applied at the vibration source or additional mitigation is required after treating the source, the next preferred placement of vibration mitigation is along the vibration propagation path between the source and receiver. Possible path treatments include:
• Trenches — Use of trenches to control ground -borne vibration is analogous to controlling airborne noise with noise barriers. This approach has not received much attention in the United States, but trenches could be a practical method for controlling transit vibration from at -grade track. A rule -of -thumb given by Richert and Ha11(60) is that if the trench is located close to the source, the trench bottom must be at least 0.6 times the Rayleigh wavelength below the vibration source.
For most soils, Rayleigh waves travel at around 600 ft/sec, which means that the wavelength at 30 Hz is 20 ft, requiring that a trench be approximately 15 ft deep to be effective at 30 Hz.
A trench can be effective as a vibration barrier if it is either open or solid. The Toronto Transit Commission tested a trench filled with Styrofoam to keep it open and reported successful performance over a period of at least one year. Solid barriers can be constructed with sheet piling or concrete poured into a trench.
• Buffer Zones — Expanding the rail ROW can be the most economical method of reducing the vibration impact by simply increasing the distance between the source and receiver. A similar approach is to 4936
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negotiate a vibration easement from the affected property owners (e.g., a row of single-family homes adjacent to a proposed commuter rail line). There may be legal limitations, however, on the ability of funding agencies to acquire land strictly for the purpose of mitigating vibration (or noise) impact.
I c. Evaluate Receiver Treatments — When vibration mitigation treatments cannot be applied at the source or along the propagation path, or if combinations of treatments are required, treatments to the receivers can be considered as described below.
■ Building Modifications — In some circumstances, it is practical to modify the affected building to reduce the vibration level. Vibration isolation of buildings consists of supporting the building foundation on elastomer pads, similar to bridge bearing pads. Vibration isolation of buildings is seldom an option for existing buildings and is typically only possible for new construction. Vibration impacts on sensitive laboratory instruments, such as electron microscopes, may be controlled with vibration isolation tables.
This approach is particularly important for shared -use facilities such as an office space above a transit station or terminal. When vibration - sensitive equipment such as electron microscopes will be affected by transit vibration, specific modifications to the building structure may be the most cost-effective method of controlling the impact aside from modification of equipment mounting systems. For example, the floor upon which the vibration -sensitive equipment is located could be stiffened and isolated from the remainder of the building to reduce the vibration. Alternatively, the equipment mounting systems could be modified or the equipment could be relocated to a different building at far less cost.
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SECTION Noise and Vibration during
7 Construction
Construction noise and vibration often generates complaints from the community, even when construction is for a limited timeframe. Public concerns about construction noise and vibration increase considerably with lengthy periods of heavy construction on major projects as well as prevalence of nighttime construction (often scheduled to avoid disrupting workday road and rail traffic). Noise and vibration complaints typically arise from interference with people's activities, especially when the adjacent community has no clear understanding of the extent or duration of the construction. Misunderstandings can arise when the community thinks a contractor is being insensitive, and the contractor believes it is performing the work in compliance with local ordinances. This situation underscores the need for early identification and assessment of potential problem areas.
This section outlines the procedures for assessing noise and vibration impacts during construction. The type of assessment (qualitative or quantitative) and the level of analysis are determined based on the scale of the project and surrounding land uses. In cases where a full quantitative assessment is not warranted, a qualitative assessment of the construction noise and vibration environment can lead to greater understanding and tolerance in the community.
For major projects with extended periods of construction at specific locations, a quantitative assessment can aid contractors in making bids by allowing changes in construction approach and including mitigation costs before the construction plans are finalized.
Generally, local noise ordinances are not very useful for evaluating construction noise impact. They usually relate to nuisance and hours of allowed activity, and sometimes specify limits in terms of maximum levels, but are generally not practical for assessing the impact of a construction project. Project construction noise criteria should take into account the existing noise environment, the absolute noise levels during construction activities, the duration of the construction, and the adjacent land uses. While it is not the purpose of this manual to specify standardized criteria for construction noise impact, the following guidelines can be considered reasonable criteria for assessment. If these criteria are exceeded, there may be adverse community reaction.
Procedures for assessing construction noise are presented in Section 7. I .
Procedures for assessing construction vibration are presented in Section 7.2.
7. I Construction Noise Assessment
Noise impacts from construction may vary greatly depending on the duration and complexity of the project. The key elements of the Construction Noise Assessment procedure and recommended workflow are as follows. 4938
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Step I: Determine Level of Construction Noise Assessment Step 2: Use a Qualitative Construction Noise Assessment to Estimate Construction Noise
Step 3: Use a Quantitative Construction Noise Assessment to Estimate Construction Noise
Step 4: Assess Construction Noise Impact
Step 5: Determine Construction Noise Mitigation Measures If there is uncertainty in how to determine the appropriate level of assessment, contact the FTA Regional office.
Step I : Determine Level of Construction Noise
Assessment
Determine the appropriate level of assessment based on the scale and type of the project and depending on the stage of environmental review.
Consider the following factors:
■ Scale of the project
■ Proximity of noise -sensitive sites to the construction zones ■ Number of noise -sensitive receivers in the project area ■ Duration of construction activities near noise -sensitive receivers ■ Schedule, including the construction days, hours, and time periods ■ Method (e.g., cut -and -cover vs. bored tunneling)
■ Concern about construction noise expressed in comments by the general public (e.g., through scoping or public meetings) I a. Determine if an assessment is required — Construction Noise Assessments are not required for many small projects including:
■ Installation of safety features like grade -crossing signals; ■ Track improvements within the ROW; or
■ Erecting small buildings and facilities which are similar in scale to the surrounding development.
For small projects like these, include descriptions in the environmental document of the length of construction, the loudest equipment to be used, the expected truck access routes, the avoidance of nighttime activity, and any other relevant planned construction method.
I b. Determine whether a qualitative or quantitative assessment is required
■ Qualitative Construction Noise Assessment — Qualitative Construction Noise Assessments may be required for projects with less than a month of construction time in a noise -sensitive area. See Step 2 for more information on Qualitative Construction Noise Assessments.
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• Quantitative Construction Noise Assessments — Quantitative Construction Noise Assessments may be required for projects with a month or more of construction in noise -sensitive areas or if particularly noisy equipment will be involved. See Step 3 for more information on Quantitative Construction Noise Assessments.
Step 2: Use a Qualitative Construction Noise Assessment to Estimate Construction Noise
Use a qualitative construction noise assessment to estimate construction noise for appropriate projects per Section 7.1, Step I b.
Provide qualitative descriptions in the environmental document of the following elements:
• Duration of construction (both overall and at specific locations) • Equipment expected to be used (e.g., noisiest equipment) • Schedule with limits on times of operation (e.g., daytime use only) • Monitoring of noise
• Forum for communicating with the public
• Commitments to limit noise levels to certain levels, including any local ordinances that apply
• Consideration of application of noise control treatments used successfully in other projects
Effective community outreach and relations are important for these projects.
Disseminate information to the public early regarding the kinds of construction equipment, expected noise levels, and durations to forewarn potentially affected neighbors about the temporary inconvenience. Including a general description of the variation of noise levels during a typical construction day may also be helpful.
Note that the construction criteria in Step 4 do not apply to qualitative assessments.
Step 3: Use a Quantitative Construction Noise Assessment to Estimate Construction Noise
Use a quantitative construction noise assessment to estimate construction noise for appropriate projects per Section 7.1, Step I b.
For Quantitative Construction Noise Assessments, follow the recommended procedure in this step and include a description of the planned construction methods and any basic measures that have been identified to reduce the potential impact, such as prohibiting the noisiest construction activities during the nighttime, in the environmental document. It may be prudent, however, to defer final decisions on noise control measures until the project and construction plans are defined in greater detail during the engineering phase. • Noise Source Levels from Typical Construction Equipment and Operations — The noise levels generated by construction 4940
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equipment vary greatly on factors such as the type of equipment, the equipment model, the operation being performed, and the condition of the equipment. Typically, the dominant source of noise from most construction equipment is the engine, often a diesel engine, which usually does not have sufficient muffling. In other cases, such as impact pile -driving or pavement -breaking, noise generated by the process dominates. Construction equipment can be considered to operate in the following two modes for Construction Noise Assessments:
▪ Stationary - Stationary equipment operates in one location for one or more days at a time, with either a fixed power operation (pumps, generators, compressors) or a variable noise operation (pile drivers, pavement breakers).
• Mobile — Mobile equipment moves around the construction site with power applied in cyclic fashion (bulldozers, loaders), or to and from the site (trucks). Movement around the site is considered in the construction noise prediction procedure.
Variation in power imposes additional complexity in characterizing the noise source level from mobile equipment. Describe the noise at a reference distance from the equipment operating at full power and adjusting it based on the duty cycle of the activity to determine the Leg(t) of the operation.
Typical noise levels from representative equipment are included in Table 7-1.
The levels are based on an EPA Report,(61) measured data from railroad construction equipment taken during the 1976 Northeast Corridor Improvement Project, the FHWA Roadway Construction Noise Model, and other measured data.
For equipment that is not represented in Table 7-I, measure the noise levels according to the standard procedures for measuring the exterior noise levels for the certification of mobile and stationary construction equipment by the Society of Automotive Engineers.(62)(63)
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Table 7-I Construction Equipment Noise Emission Levels
Equipment
Typical Noise Level 50 ft
from Source, dBA
Air Compressor
80 Backhoe
80 Ballast Equalizer
82 Ballast Tamper
83 Compactor
82 Concrete Mixer
85 Concrete Pump
82 Concrete Vibrator
76 Crane, Derrick
88 Crane, Mobile
83 Dozer
85 Generator
82 Grader
85 Impact Wrench
85 Jack Hammer
88 Loader
80 Paver
85 Pile-driver (Impact)
101
Pile-driver (Sonic)
95 Pneumatic Tool
85 Pump
77 Rail Saw
90 Rock Drill
95 Roller
85 Saw
76 Scarifier
83 Scraper
85 Shovel
82 Spike Driver
77 Tie Cutter
84 Tie Handler
80 Tie Inserter
85 Truck
84 3a. Use the metric Leq(t) to assess construction noise. This unit is appropriate because Leq(t) can be used to describe:
• Noise level from operation of each piece of equipment separately, and levels can be combined to represent the noise level from all equipment operating during a given period
• Noise level during an entire phase
• Average noise over all phases of the construction
3b. Use Eq. 7- I to predict construction noise impact for major transit projects, considering the noise generated by the equipment and noise propagation due to distance. Calculate Leq.equip for all equipment individually, then use decibel addition to sum the LAeq.equip for all equipment operating during the same time period. See Appendix B. I . I for information on decibel addition.
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Leq.equip - Lemission + 101og(Adjusage) — 20 log(—) — 10G1og(D) Eq. 7-I SO 50
where:
Leq,equip
Lemission
Ad)usage
D
G
= Leq(r)at a receiver from the operation of a single piece of equipment over a specified time period, dBA
= noise emission level of the particular piece of equipment at the reference distance of 50 ft, dBA
= usage factor to account for the fraction of time that the equipment is in use over the specified time period
= distance from the receiver to the piece of equipment, ft = a constant that accounts for topography and ground effects Determine the quantities for Eq. 7- I based on the level of assessment as described below.
• A general assessment of construction noise is warranted for projects in an early assessment stage when the equipment roster and schedule are undefined and only a rough estimate of construction noise levels is practical.
• A detailed analysis of construction noise is warranted when many noise - sensitive sites are adjacent to a construction project or where contractors are faced with stringent local ordinances or heightened public concerns expressed in early outreach efforts.
Complete the appropriate assessment for each phase of construction. Major construction projects are accomplished in several different phases. Each phase has a specific equipment mix, depending on the work to be accomplished during that phase. As a result of the equipment mix, each phase has its own noise characteristics; some phases have higher continuous noise levels than others, and some have higher impact noise levels than others.
Option A: General Assessment — Determine the quantities for Eq. 7- I based on the following assumptions for a General Assessment of each phase of construction.
• Noise emission level (Lemission) — Determine the emission level at 50 ft according to noise from typical construction equipment described above and Table 7-1.
• Usage factor (Adjusage) — Assume a usage factor of I. This assumes a time period of one -hour with full power operation. Most construction equipment operates continuously for periods of one -hour or more during the construction period.
Therefore, 10log(Adjusage/ = 0 and can be omitted from the equation. • Distance (D) — Assume that all equipment operates at the center of the project, or centerline for guideway or highway construction project. 4943
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• Ground effect (G) - G = 0 assuming free -field conditions and ignoring ground effects. If ground effects are of specific importance to the assessment, consider using the Detailed Analysis procedure.
Only determine the Leq.equip for the two noisiest pieces of equipment expected to be used in each phase of construction. Then, sum the levels for each phase of construction using decibel addition.
Option B: Detailed Analysis — Determine the quantities for Eq. 7- I based on the following assumptions for a Detailed Analysis of each phase of construction.
Alternatively, for detailed, long-term, and complex construction projects or projects near a particularly sensitive site, the FHWA's Windows -based screening tool, "Roadway Construction Noise Model (RCNM)," can be used for the prediction of construction noise.(64)
• Noise emission level (Lemission)— Measure or certify the noise emission level for each piece of equipment.
• Usage factor (Adjusaye) — Long-term construction project noise impact is based on a 30 -day average Ld,,, the times of day of construction activity (nighttime noise is penalized by I0 dB in residential areas), and the percentage of time the equipment is used during a period of time that will affect Adjusaye•
For example, an 8 -hour Leq(t) is determined by making Adjusayethe percentage of time each individual piece of equipment operates under full power in that period. Similarly, the 30 -day average Ldr, is determined from the Adjusaye expressed by the percentage of time the equipment is used during the daytime hours (7 a.m. to I0 p.m.) and nighttime (I0 p.m. to 7 a.m.), separately, over a 30 -day period. To account for increased sensitivity to nighttime noise, the nighttime noise levels are adjusted by I 0 dB in the Ldn computation (see Appendix B.I.4.5). • Distance (D) — Determine the location of each piece of equipment during operation and the distance to each receiver.
• Ground effect (G) — Use Table 4-26 in Section 4.5, Step 3 to calculate G to account for the site topography, natural and man-made barriers, and ground effects.
Compute the 8 -hour Leq(t) ( Leq.equip(8hr)) and the 30 -day average Ldn (Ldn.equip(3oday)) for all equipment expected to be used in each phase of construction separately. Then, sum the levels for each phase of construction using Eq. 4-56 and Eq. 4-57 in Table 4-32.
Step 4: Assess Construction Noise Impact
Compare the predicted noise levels from the Quantitative Construction Noise Assessment with impact criteria to assess impact from construction noise for each phase of construction.
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No standardized criteria have been developed for assessing construction noise impact. Consequently, criteria must be developed on a project -specific basis unless local ordinances apply. As stated earlier in this section, local noise ordinances are typically not very useful in evaluating construction noise. They usually relate to nuisance and hours of allowed activity, and sometimes specify limits in terms of maximum levels, but are generally not practical for assessing the impact of a construction project. Project construction noise criteria should account for the existing noise environment, the absolute noise levels during construction activities, the duration of the construction, and the adjacent land use. While it is not the purpose of this manual to specify standardized criteria for construction noise impact, the following guidelines can be considered reasonable criteria for assessment. If these criteria are exceeded, there may be adverse community reaction.
The construction impact guidelines are presented based on the level of quantitative assessment.
Option A: General Assessment — Compare the combined Leq.equip(1hr) for the two noisiest pieces of equipment for each phase of construction determined in Section 7.1, Step 3 to the criteria below. Then, identify locations where the level exceeds the criteria.
Table 7-2 General Assessment Construction Noise Criteria Land Use
Leq.equip(1hr),
Day
dBA
Night
Residential
90 80
Commercial
100
100
Industrial
100
100
Option B: Detailed Analysis — Compare the combined Leq.equip(lhr) and the combined Ldn.equip(3oday) for all equipment for each phase of construction determined in Section 7.1, Step 3 to the criteria below. Then, identify locations where the level exceeds the criteria.
Table 7-3 Detailed Analysis Construction Noise Criteria Land Use
Leq•equip(8hr), dBA
Day Night
Ldn.equip(30day), dBA
30 -day Average
Residential
80 70
75 Commercial
85 85
80*
Industrial
90 90
85*
*Use a 24 -hour Leq(24hr) instead of Ldn.equip(30day).
Step 5: Determine Construction Noise Mitigation
Measures
Evaluate the need for mitigation and select appropriate mitigation measures.
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Where potential impacts have been identified according to Section 7.1, Step 4, evaluate appropriate control measures. Include descriptions of how each affected location will be treated with one or more mitigation measures in the environmental document.
5a. Determine the appropriate approach for construction noise control.
Categories of approaches include:
• Design considerations and project layout
▪ Construct noise barriers, such as temporary walls or piles of excavated material, between noisy activities and noise -sensitive receivers.
▪ Re-route truck traffic away from residential streets. Select streets with the fewest homes if no alternatives are available. ▪ Site equipment on the construction lot as far away from noise - sensitive sites as possible.
▪ Construct walled enclosures around especially noisy activities or clusters of noisy equipment. For example, shields can be used around pavement breakers, and loaded vinyl curtains can be draped under elevated structures.
• Sequence of operations
▪ Combine noisy operations to occur in the same time period. The total noise level produced will not be substantially greater than the level produced if the operations were performed separately. ▪ Avoid nighttime activities. Sensitivity to noise increases during the nighttime hours in residential neighborhoods.
• Alternative construction methods
• Avoid impact pile -driving where possible in noise -sensitive areas.
Drilled piles or the use of a sonic/vibratory pile driver or push pile driver are quieter alternatives where the geological conditions permit their use.
• Use specially -quieted equipment, such as quieted and enclosed air compressors and properly -working mufflers on all engines. • Select quieter demolition methods. For example, sawing bridge decks into sections that can be loaded onto trucks results in lower cumulative noise levels than impact demolition by pavement breakers.
Include descriptions of how each impacted location will be treated with one or more mitigation measures in the environmental impact assessment when possible.
5b. Describe and commit to a mitigation plan that will be developed later when the information is available to make final decisions (not often available during the project development phase) on all specific mitigation measures. This may be the case for large, complex projects. The objective of the plan should be to minimize construction noise using all reasonable (e.g., cost vs. benefit) and feasible (e.g., possible to construct) means available. 4946
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Components of a mitigation plan may include some or all of the following provisions, which should also be specified in construction contracts:
• Equipment noise emission limits — Equipment noise limits are absolute noise limits applied to generic classes of equipment at a reference distance (typically 50 ft). The limits should be set no higher than what is reasonably achievable for well -maintained equipment with effective mufflers. Lower limits that require source noise control may be appropriate for certain equipment when needed to minimize community noise impact, if reasonable and feasible. Provisions could also be included to require equipment noise certification testing prior to use on -site.
• Lot -line construction noise limits — Lot -line construction noise limits are noise limits that apply at the lot -line of specific noise -sensitive properties. The limits are typically specified in terms of both noise exposure (usually Leg(t) over a 20 -30 -minute period) and maximum noise level. They should be based on local noise ordinances if applicable, as well as pre -construction baseline noise levels (usually 3 to 5 dB above the baseline).
• Operational and/or equipment restrictions — It may be necessary to prohibit or restrict certain construction equipment and activities near residential areas during nighttime hours. This is particularly true for activities that generate tonal, impulsive, or repetitive sounds, such as back-up alarms, hoe ram demolition, and pile -driving.
• Noise abatement requirements — In some cases, specifications may be provided for particular noise control treatments based on the results of the design analysis and/or prior commitments made to the public by civic authorities. An example would be the requirement for a temporary noise barrier to shield a particular community area from noisy construction activities.
• Noise monitoring plan requirements — Plans can be developed for pre -project noise monitoring to establish baseline noise levels at sensitive locations, as well as for periodic equipment and lot -line noise monitoring during the construction period. The plan should outline the measurement and reporting methods that will be used to demonstrate compliance with the project noise limits.
• Noise control plan requirements — For major construction projects, preparation and submission of noise control plans on a periodic basis (e.g., every six months) are generally required. These plans should predict the construction noise at noise -sensitive receiver locations based on the proposed construction equipment and methods.
If the analysis predicts that the specified noise limits will be exceeded, the plan should specify the mitigation measures that will be applied and should demonstrate the expected noise reductions these measures will achieve. The objective of this proactive approach is to minimize the 4947
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likelihood of community noise complaints by ensuring that any necessary mitigation measures are included in the construction plans. • Compliance enforcement program — If construction noise is an issue in the community, it is important that a program be implemented to monitor contractor compliance with the noise control specifications and mitigation plan. It is recommended that this function be performed by a construction management team on behalf of the public agency. • Public information and complaint response procedures — To maintain positive community relations, it is recommended to keep the public informed about the construction plans and efforts to minimize noise, and procedures should be established for prompt response and corrective action to noise complaints during construction.
Most of these provisions are appropriate for large-scale projects, where construction activity will continue for many months, if not years. The linked references contain more information on construction noise for major transportation projects.(60)(65)
7.2 Construction Vibration Assessment
Construction activity can result in varying degrees of ground vibration, depending on the equipment and methods employed. Operation of construction equipment causes ground vibrations that spread through the ground and diminish in strength with distance. Buildings founded on the soil near the construction site respond to these vibrations with varying results, ranging from no perceptible effects at the lowest levels, low rumbling sounds and perceptible vibrations at moderate levels, and slight damage at the highest levels.
While ground vibrations from construction activities do not often reach the levels that can damage structures, fragile buildings must receive special consideration. The construction vibration criteria include consideration of the building condition.
The key elements of the Construction Vibration Assessment procedures and recommended workflow are as follows:
Step I: Determine level of construction vibration assessment Step 2: Use a qualitative construction vibration assessment Step 3: Use a quantitative construction vibration assessment Step 4: Assess construction vibration impact
Step 5: Determine construction vibration mitigation measures 4948
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Step I: Determine Level of Construction Vibration
Assessment
Determine the appropriate level of assessment based on the sca/e and type of the project and the stage of environmental review.
I a. Determine if an assessment is required.
Construction Vibration Assessments are not required for many small projects including:
■ Installation of safety features like grade -crossing signals ■ Track improvements within the ROW
■ Erecting small buildings and facilities, which are similar in scale to the surrounding development
I b. Determine whether a qualitative or quantitative assessment is required.
■ Qualitative Construction Vibration Assessment — A qualitative construction vibration assessment is appropriate for projects where prolonged annoyance or damage from construction vibration is not expected. For example, equipment that generates little or no ground vibration —such as air compressors, light trucks, and hydraulic loaders — only require qualitative descriptions. See Section 7.2, Step 2 for more information on qualitative construction vibration assessments. ■ Quantitative Construction Vibration Assessment — A
quantitative construction vibration analysis is appropriate for projects where construction vibration may result in building damage or prolonged annoyance. For example, activities such as blasting, pile - driving, vibratory compaction, demolition, and drilling or excavation near sensitive structures require a quantitative analysis. See Section 7.2, Step 3 for more information on quantitative construction vibration assessments.
If there is uncertainty in how to determine the appropriate level of assessment, contact the FTA Regional office.
Step 2: Use a Qualitative Construction Vibration
Assessment
Use a qualitative construction vibration assessment to estimate vibration for appropriate projects per Section 7.2, Step I b.
Provide qualitative descriptions in the environmental document of the following elements:
■ Duration of construction (both overall and at specific locations) ■ Equipment expected to be used
■ Description of how ground -borne vibration will be maintained at an acceptable level
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Note that the criteria in Section 7.2, Step 4 do not apply to qualitative assessments.
Step 3: Use a Quantitative Construction Vibration
Assessment
Use a quantitative construction vibration assessment to estimate vibration for appropriate projects per Section 7.2, Step 1 b.
For quantitative construction vibration assessments, follow the recommended procedure in this step. Vibration source levels from typical construction equipment and operations are provided below, and procedures on how to estimate construction vibration for damage and annoyance are provided in Steps 3a and 3b, respectively.
• Vibration Source Levels from Construction Equipment — Table 7-4 presents average source levels in terms of velocity for various types of construction equipment measured under a wide variety of construction activities. The approximate rms vibration velocity levels were calculated from the PPV limits using a crest factor of 4, representing a PPV-rms difference of 12 dB. Note that although the table gives one level for each piece of equipment, there is considerable variation in reported ground vibration levels from construction activities. The data in Table 7-4 provide a reasonable estimate for a wide range of soil conditions.(66)(67)(68)(69)
Table 7-4 Vibration Source Levels for Construction Equipment Equipment
PPV at 25
ft, in/sec
Approximate
Lv* at 25 ft
Pile Driver (impact)
upper range
1.518
1 12
typical
0.644
104
Pile Driver (sonic)
upper range
0.734
I05
typical
0.17 93
Clam shovel drop (slurry wall)
0.202
94 Hydromill (slurry
wall)
in soil
0.008
66 in rock
0.017
75 Vibratory Roller
0.21 94
Hoe Ram
0.089
87 Large bulldozer
0.089
87 Caisson drilling
0.089
87 Loaded trucks
0.076
86 Jackhammer
0.035
79 Small bulldozer
0.003
58 RMS velocity in decibels, VdB re I micro-in/sec
3a. Damage Assessment
Assess for building damage for each piece of equipment individually.
Construction vibration is generally assessed in terms of peak particle velocity (PPV), as described in Section S.I.
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• Determine the vibration source level (PPVref) for each piece of equipment at a reference distance of 25 ft as described above and in Table 7-4.
• Use Eq. 7-2 to apply the propagation adjustment to the source reference level to account for the distance from the equipment to the receiver. Note that the equation is based on point sources with normal propagation conditions.
251.5
PPVequip = PPVref x (D )
where:
PPVequip
PPVref
D
Eq. 7-2
= the peak particle velocity of the equipment
adjusted for distance, in/sec
= the source reference vibration level at 25 ft,
in/sec
= distance from the equipment to the receiver, ft
3b. Annoyance Assessment
Assess for annoyance for each piece of equipment individually. Ground -borne vibration related to human annoyance is related to rms velocity levels, expressed in VdB as described in Section 5. I .
Estimate the vibration level (Lv) using Eq. 7-3.
D
Lv.distance = Lvref — 301og(25)
where:
Lv.distance
Lvref
D
= the rms velocity level adjusted for distance, VdB
= the source reference vibration level at 25 ft, VdB
= distance from the equipment to the receiver, ft
Eq. 7-3
Step 4: Assess Construction Vibration Impact
Compare the predicted vibration levels from the Quantitative Construction Vibration Assessment with impact criteria to assess impact from construction vibration.
Assess potential damage effects from construction vibration for each piece of equipment individually. Note that equipment operating at the same time could increase vibration levels substantially, but predicting any increase could be difficult. The criteria presented in this section should be used during the environmental impact assessment phase to identify problem locations that must be addressed during the engineering phase.
Compare the PPV and approximate L,, for each piece of equipment determined in Section 7.2, Step 3 to the vibration damage criteria in Table 7-5, which is presented by building/structural category, to assess impact.(70)(71) The approximate rms vibration velocity levels were calculated from the PPV limits using a crest factor of 4.
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Table 7-5 Construction Vibration Damage Criteria
Building/ Structural Category
PPV, in/sec
Approximate Lv*
I. Reinforced -concrete, steel or timber (no plaster)
0.5 102
II. Engineered concrete and masonry (no plaster)
0.3 98
III. Non -engineered timber and masonry buildings
0.2 94
IV. Buildings extremely susceptible to vibration damage
0.12 90
*RMS velocity in decibels, VdB re I micro-in/sec
Compare the Lv determined in Section 7.2, Step 3 to the criteria for the General Vibration Assessment in Section 6.2 to assess annoyance or interference with vibration -sensitive activities due to construction vibration.
Step 5: Determine Construction Vibration Mitigation
Measures
Evaluate the need for mitigation and select appropriate mitigation measures where potential human impacts or building damage from construction vibration have been identified according to Section 7.2, Step 4.
5a. Determine the appropriate approach for construction vibration mitigation considering equipment location and processes.
• Design considerations and project layout
• Route heavily -loaded trucks away from residential streets. Select streets with the fewest homes if no alternatives are available. ▪ Operate earth -moving equipment on the construction lot as far away from vibration -sensitive sites as possible.
• Sequence of operations
• Phase demolition, earth -moving, and ground -impacting operations so as not to occur in the same time period. Unlike noise, the total vibration level produced could be substantially less when each vibration source operates separately.
▪ Avoid nighttime activities. Sensitivity to vibration increases during the nighttime hours in residential neighborhoods.
• Alternative construction methods
• Carefully consider the use of impact pile -driving versus drilled piles or the use of a sonic/vibratory pile driver or push pile driver where those processes might create lower vibration levels if geological conditions permit their use.
— Pile -driving is one of the greatest sources of vibration associated with equipment used during construction of a project. The source levels in Table 7-4 indicate that sonic pile drivers may provide substantial reduction of vibration levels compared to impact pile drivers. But, there are some additional vibration effects of sonic pile drivers that may limit their use in sensitive locations.
— A sonic pile driver operates by continuously shaking the pile at a fixed frequency, literally vibrating it into the ground. Continuous operation at a fixed frequency may, however, be more
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noticeable to nearby residents, even at lower vibration levels.
Furthermore, the steady-state excitation of the ground may induce a growth in the resonant response of building
components. Resonant response may be unacceptable in cases of fragile buildings or vibration -sensitive manufacturing processes. Impact pile drivers, however, produce a high vibration level for a short time (0.2 seconds) with sufficient time between impacts to allow any resonant response to decay.
Select demolition methods involving little to no impact, where possible. For example, sawing bridge decks into sections that can be loaded onto trucks results in lower vibration levels than impact demolition by pavement breakers. Milling generates lower vibration levels than excavation using clam shell or chisel drops.
Avoid vibratory rollers and packers near sensitive areas. 5b. Describe and commit to a mitigation plan that will be developed and implemented during the engineering and construction phase when the information available during the project development phase will not be sufficient to define specific construction vibration mitigation measures. The objective of the plan should be to minimize construction vibration damage using all reasonable and feasible means available. The plan should include the following components:
■ A procedure for establishing threshold and limiting vibration values for potentially affected structures, based on an assessment of each structure's ability to withstand the loads and displacements due to construction vibrations
■ A commitment to develop a vibration monitoring plan during the engineering phase and to implement a compliance monitoring program during construction
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SECTION Documentation of Noise and
8 Vibration Assessment
The level of required documentation is determined according to the project class of action. Section 2.I covers the appropriate class of action (EIS, EA, or CE) for different projects. If there is uncertainty in the appropriate level of documentation, contact the FTA Regional office.
The noise and vibration analysis must be articulated to the public in a clear, comprehensive manner for all levels of documentation. The technical data and information necessary to withstand scrutiny in the environmental review process must be documented in a way that remains intelligible to the public.
Justification for all assumptions used in the analysis, such as selection of representative measurement sites and all baseline conditions, must be presented for review.
A separate technical report or memorandum is often prepared as a supplement to the environmental document. A technical report is appropriate in cases when including the data from the assessment would create an unreasonably long environmental document. The details of the analysis are important for establishing the basis for the assessment. Therefore, all details in the technical report should be contained in a well -organized format for easy access to the information.
For large-scale projects, the environmental document should contain a summary of the essential analysis information to provide subject matter context and the analysis findings. For these projects, separate technical reports are usually prepared as supplements to the EIS or EA and referred to in the environmental document. For smaller projects, or projects with minimal noise or vibration impact, all of the technical information may be presented in the environmental document itself or in a technical memorandum. Other projects might have no potential for noise or vibration impacts. For those projects, that environmental documentation should explain that no noise or vibration impacts are expected.
This section provides guidance on presenting the necessary noise and vibration information in the environmental document (Section 8. I) and the associated technical report (Section 8.2).
8.I Environmental Document
In the environmental document, provide a summary of the comprehensive noise and vibration information from the technical report and emphasize the salient points of the analysis in a format and style that the public can understand.
Smaller projects may have all of the technical information contained within the environmental document, so take special care in summarizing the technical details to convey the information adequately.
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Step I: Choose the Information to Include
Choose the appropriate noise and vibration analysis information to include based on the level of environmental review and the associated documentation.
I a. Provide full disclosure of noise and vibration impacts in the environmental document, including identification of locations where impacts cannot be mitigated below the severe impact level. In general, an EIS describes significant impacts and plans to mitigate the impacts. For EAs, completion of the environmental review with a finding of no significant impact (FONSI) may depend on mitigation being considered for incorporation in the proposed project. The way mitigation is presented in the environmental document depends on the type of impact (noise or vibration) and the stage of project development and environmental review. Projects that meet the criteria of a CE may also require the completion of a noise and/or vibration analysis, and the results of such an analysis should be documented in a noise memo or the CE documentation.
I b. Document noise impacts — Typically, airborne noise impacts can be accurately predicted during the environmental review. For projects that focus on a single alternative, noise impacts can be accurately identified in the draft environmental document. If mitigation is anticipated, then mitigation options should be explored in the EA or draft EIS; firm decisions on mitigation can be deferred to the final document. But for all projects, decisions on noise mitigation should be made before the final document is approved.
I c. Document vibration impacts — Predicting vibration impacts accurately is more complex because ground -borne vibration may be strongly influenced by subsurface conditions. The geotechnical studies that reveal these conditions are normally undertaken during the engineering phase, after the environmental review process is complete. Therefore, the final environmental document will usually not be able to state with certainty whether mitigation is needed for ground -borne vibration and noise.
If the engineering phase is conducted at the same time as the final environmental document, report the results of the Detailed Vibration Analysis in the final environmental document. If the engineering phase is conducted after the final environmental document, report the results of the General Vibration Assessment in the final environmental document. If impact is determined, include a commitment in the final document to conduct a Detailed Vibration Analysis during the engineering phase to complete the impact assessment. Also, include a discussion on various control measures that could be used and the likelihood that the criteria could be met through the use of one or more of the measures. It may be possible to state a commitment in the final environmental document to adhere to the impact criteria for the Detailed Vibration Analysis, while deferring the selection of specific vibration control measures until the completion of detailed studies in the engineering phase. When work is conducted after FTA signs its final decision document (i.e., ROD, combined FEIS/ROD, or FONSI), additional documentation, such as a reevaluation of the previous decision, may be necessary. FTA recommends contacting the FTA Regional office directly in these situations.
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I d. Describe mitigation measures in the decision document — After the decision document is approved, incorporate the mitigation measures by reference in the actual grant agreements signed by FTA and the project sponsor.
The mitigation measures then become contractual conditions that must be adhered to by the project sponsor.
It is typically appropriate to include the following noise and vibration information in the environmental document, as described in Section 8. I:
• The existing conditions (affected environment)
• The direct impacts from operation (environmental consequences) • The construction impacts (environmental consequences) Step 2: Organize information in the Environmental
Document
Include information in the following sections of the environmental document separating out the noise and vibration information.
2a. Existing Conditions (Affected Environment) — Describe the existing conditions (conditions without the project) in terms of the existing noise and vibration conditions in this section of the document. The primary function of this section is to establish the focus and baseline conditions for the discussion of environmental impacts. Include the following basic information and separate the noise and vibration sections. • Description of noise/vibration metrics, effects and typical levels — Include a targeted summary of relevant information from Section 3 of this manual. This will serve as background for the discussions of noise/vibration levels and characteristics that will follow in later sections. Provide illustrative material to convey typical levels to the public.
• Inventory of noise/vibration-sensitive sites — Describe the approach for identifying noise- and vibration -sensitive sites as well as the identified sites and site descriptions. Use sufficient detail to demonstrate completeness. Document these results on a map.
• Noise/vibration measurements — Document the basis for selecting measurement sites, including tables of sites coordinated with maps showing locations of sites. Summarize the measurement approach and include the justification for the measurement procedures used.
Present measurement data in well -organized tables and figures with a summary and interpretation of measured data. Measurements are often included in the table of measurement sites described in the previous paragraph. In some cases, measurements may be supplemented or replaced by collected data relevant to the noise and vibration characteristics of the area. For example, soil information for estimating ground -borne vibration propagation characteristics may be available from other projects in the area.
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A summary and interpretation of how the collected data define the project setting is fundamental to this section.
2b. Direct Impacts — Include the following in the discussion on direct impacts due to project operation:
• Overview of approach — Provide a targeted summary of relevant information on the assessment procedure for determining noise/vibration impacts as a framework for the following sections. • Estimated noise/vibration levels — Provide a general description of prediction models used to estimate project noise/vibration levels.
Describe any distinguishing features unique to the project, such as source levels associated with various technologies.
Describe the results of the predictions in general terms first, followed by a detailed accounting of predicted noise levels. Supplement this information with tables and illustrate by contours, cross -sections, or shaded mapping. If contours are included in a technical report, it is not necessary to repeat them in this section.
• Criteria for noise/vibration impact — Describe the impact criteria for the project in detail and reference the appropriate section in this manual. Include tables listing the criteria levels or the figures included in this manual.
• Noise/vibration impact assessment — Present the impact assessment in its own section or combined with the section above.
Describe the locations, as identified in the screening procedure, where noise/vibration impact is expected to occur without implementation of mitigation measures, based on the screening results, predicted future levels, existing levels, and application of the impact criteria.
Include inventory tables of impacted noise- and vibration -sensitive sites to quantify the impacts for all noise/vibration-sensitive sites included in the Affected Environment (Existing Conditions) as described in the Existing Conditions section above.
• Noise/vibration mitigation measures — Perhaps the greatest difference between the technical report and the environmental document is with mitigation. The technical report discusses mitigation options and recommendations, while the environmental document provides the vehicle for reaching decisions on appropriate mitigation measures.
Begin this section with a summary of the noise/vibration mitigation measures considered for the impacted locations. Describe the specific measures selected for implementation in detail. Also, include any 4957
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applicable, specific noise or vibration policies the project sponsor may have in place.
In cases where it is not possible to commit to a specific mitigation measure in the final environmental document, it may be possible to commit to a certain noise/vibration level. For example, the environmental document could include a commitment to meet or exceed the impact criteria specified in Sections 4. I and 6.2. ■ Unavoidable adverse environmental effects — If it is projected that adverse noise/vibration impacts will result after all reasonable abatement measures have been incorporated, identify these impacts in this section.
2c. Construction Impacts — Discuss construction impacts in the environmental document's section on construction impacts, if present.
If, because of the scale of the project, the environmental document does not have a separate construction impacts section, then the construction impacts should be discussed with the rest of the resource impacts.
When a special section on construction noise/vibration impacts is included in the document, it should be organized according to the comprehensive outline on long-term impacts described above. For projects with relatively minor effects, include a brief summary of impact.
8.2 Technical Report on Noise and Vibration
The technical report is intended to present complete technical data and descriptions in a manner that can be understood by the general public, but is more technical than the information found in the environmental document. All necessary background information should be present in the technical report, including tables, maps, charts, drawings, and references that may be too detailed for the environmental document, but which are important in helping to draw conclusions about the project's noise and vibration impacts and mitigation options.
Include the following major subject headings and key information described below. If both noise and vibration have been assessed, include separate sections for noise and vibration with subsections for key information as described below.
Additional details on documentation requirements for the technical report of non-standard procedures and methodologies are included in Appendix G. ■ Overview — Include a brief description of the project and an overview of the noise/vibration concerns to highlight initial considerations in framing the scope of the study.
■ Inventory of Noise/Vibration-Sensitive Sites — Describe the approach for identifying noise- and vibration -sensitive sites as well as the identified sites and site descriptions. Use sufficient detail to demonstrate completeness. Document results on a map.
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■ Measurements of Existing Noise/Vibration Conditions
▪ Document the basis for selecting measurement sites, including tables of sites coordinated with maps showing locations of sites.
Summarize the measurement approach with justification for the measurement procedures used.
• If the measurement data are used to estimate existing conditions at other locations, include the rationale and the method of estimation.
Describe measurement procedures in detail.
▪ Include tables of measurement instruments documenting manufacturer, type, serial number, and date of most recent calibration by authorized testing laboratory. Document
measurement periods, including the time of day and length of time at each site to demonstrate adequate representation of ambient conditions.
▪ Present measurement data in well -organized tables and figures with a summary and interpretation of measured data.
■ Additional Measurements Related to the Project — Include detailed description of measurements and results for projects that require specialized measurements at noise- and vibration -sensitive sites.
Examples include:
▪ Outdoor -to -indoor noise level reduction of homes
• Transmission of vibration into concert halls and recording studios • Special source -level characterization
■ Predictions of Noise/Vibration from the Project
▪ Describe the prediction model used to estimate future project conditions and specific data used as input to the models. Reference the appropriate section in this manual. Document any change or extension to the models recommended in this manual, so that the validity of the adjustments can be confirmed. See Appendix G for more information.
▪ Describe in detail the modeled scenarios and why the scenarios were chosen.
▪ Tabulate computed levels and illustrate by contours, cross -sections, or shaded mapping. Illustrate noise/vibration impacts with base maps at a scale with enough detail to provide reference for the location. ■ Noise/Vibration Criteria
• Describe the impact criteria for the project in detail and reference the appropriate section in this manual. Include tables specifying the criteria levels or the figures included in this manual. • If construction noise and/or vibration assessments were conducted, include the construction criteria in a separate section with the construction assessment details. See below for more information. 4959
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■ Noise/Vibration Impact Assessment
▪ Describe the impact assessment according to the appropriate noise and/or vibration impact assessment sections in this manual. ▪ If an alternatives analysis was conducted, present a resulting impact inventory for each alternative mode or alignment in a format that allows comparison among alternatives.
• Tabulate the inventory according to the different types of affected noise- and vibration -sensitive sites. Present the results of the assessment both before and after mitigation.
• Noise/Vibration Mitigation
• Begin this section with a summary of all treatments considered, including those not carried to final consideration.
• Consider final candidate mitigation treatments separately and provide a description of the features of the treatment, including costs, expected benefit in reducing impacts, locations where the benefit would be realized, and a discussion of the practicality of alternative treatments.
▪ Include enough noise and vibration impact information to allow the project sponsor and FTA to reach decisions on mitigation prior to issuance of an environmental decision document.
• Construction Noise/Vibration Impacts
▪ Describe criteria adopted for construction noise or vibration if construction noise and/or vibration assessments were conducted. ▪ Describe the method used for predicting construction noise or vibration and include inputs to the models such as equipment roster by construction phase, equipment source levels, assumed usage factors, and other assumed site characteristics.
▪ Present predicted levels for noise- and vibration -sensitive sites and identify short-term impacts.
• In cases where construction impacts are identified, discuss feasible abatement methods using enough detail to allow construction contract documents to include mitigation measures.
• References — Provide references for all criteria, approaches, and data used in the analyses, as well as other reports related to the project that may be relied on for information, e.g., geotechnical reports. 4960
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Appendix A: Glossary of Terms
Terminology used through the manual is defined in this appendix.(49)(72) A -weighting
A standardized filter used to alter the sensitivity of a sound level meter with respect to frequency so that the instrument is less sensitive at low and high frequencies where the human ear is less sensitive. Abbreviated as dBA.
Absolute Noise
Impact
Noise that interferes with activities independent of existing noise levels and is expressed as a fixed level threshold.
Accelerometer
A transducer that converts vibratory motion to an electrical signal proportional to the acceleration of that motion.
Ambient
The pre -project background noise or vibration level, which is often used interchangeably with "existing noise" in this manual.
Amplitude
Difference between the extremes of an oscillating signal.
Alignment
The horizontal location of a railroad or transit system as described by curved and tangent track.
At -grade
Tracks on the ground surface.
Automated Guideway
Transit (AGT)
Guided steel -wheel or rubber -tired transit passenger vehicles operating singly or in multi -car trains with a fully automated system on fixed -guideways along an exclusive ROW. AGT includes personal rapid transit, group rapid transit, and automated people mover systems.
Auxiliaries
The term applied to a number of separately driven machines, operated by power from the main engine or electric generation. They include the air compressor, radiator fan, traction motor blower, and air conditioning equipment.
Ballast mat
A 2- to 3 -inch -thick elastomer mat placed under the normal track ballast on top of a rigid slab or packed sub -grade.
Ballast
Granular material placed on the trackbed for the purpose of holding the track in line and at surface.
Bus Rapid Transit
(BRT)
A type of limited -stop bus operation that relies on technology to help speed up the service. Buses can operate on exclusive transitways, high -occupancy -vehicle lanes, expressways, or ordinary streets.
Catenary
On electric railroad and LRT systems, the term describing the overhead conductor that is contacted by the pantograph or trolley, and its support structure.
Commuter rail
Conventional passenger railroad serving areas surrounding an urban center. Most commuter railroads utilize locomotive -hauled coaches, often in push-pull configuration.
Consist
The total number and type of cars, locomotives, or transit vehicles in a trainset.
Continuous welded
rail
A number of rails welded together to form unbroken lengths of track without gaps or joints.
Corrugated rail
A rough condition of alternating ridges and grooves which develops on the rail head in service.
Crest factor
The ratio of peak particle velocity to maximum RMS amplitude in an oscillating signal.
Criteria
Plural form of "criterion," the relationship between a measure of exposure (e.g., sound or vibration level) and its corresponding effect.
Cross tie
The transverse member of the track structure to which the rails are spiked or otherwise fastened to provide proper gage and to cushion, distribute, and transmit the stresses of traffic through the ballast to the trackbed.
Crossover
Two turnouts with the track between the frogs arranged to form a continuous passage between two nearby and generally parallel tracks.
Cumulative
The summation of individual sounds into a single total value related to the effect over time.
Cut
A terrain feature typically created to allow for a trackbed to be at a lower level than the surrounding ground.
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dB
See Decibel.
dBA
See A -weighting.
Decibel
The standard unit of measurement for sound pressure level and vibration level.
Technically, a decibel is the unit of level which denotes the ratio between two quantities that are proportional to power; the number of decibels is I 0 times the logarithm of this ratio. Abbreviated as dB.
DMU
Diesel -powered multiple unit. See Multiple Unit.
DNL
See Ld,,.
Electrification
A term used to describe the installation of overhead wire or third rail power distribution facilities to enable operation of trains.
Embankment
A bank of earth, rock, or other material constructed above the natural ground surface.
Equivalent level
The level of a steady sound, which, in a stated time period and at a stated location, has the same sound energy as the time -varying sound. Also, written as Leq.
Event
A passby of a vehicle (e.g., train, bus, or car) of any size consist.
Ferry boat
A transit mode comprised of vessels to carry passengers and/or vehicles over a body of water.
Fixed guideway
A public transportation facility with a separate ROW for the exclusive use of public transportation and other high -occupancy vehicles.
Flange
The vertical projection along the inner rim of a wheel that serves, together with the corresponding projection of the mating wheel of a wheel set, to keep the wheel set on the track.
Floating slab
A special track support system for vibration isolation, consisting of concrete slabs supported on resilient elements, usually rubber or similar elastomer.
Force density
Force density is the force per root distance along the track in Ib/ft"2. The force density level is the level in decibels of the force density relative to I lb/ft' and describes the vehicle force that excites the soil/rock surrounding the transit structure.
Frequency
The number of times that a periodically occurring quantity repeats itself in a specified period. With reference to noise and vibration signals, the number of cycles per second.
Frequency spectrum
Distribution of frequency components of a noise or vibration signal.
Frog
A track structure used at the intersection of two running rails to provide support for wheels and passageways for their flanges, thus permitting wheels on either rail to cross the other.
Gage (of track)
The distance between the rails on a track.
Grade crossing
The point where a rail line and a motor vehicle road intersect at the same vertical elevation.
Guideway
Supporting structure to form a track for rolling or magnetically -levitated vehicles.
Head -End Power
(HEP)
A system of furnishing electric power for a complete railway train from a single generating plant in the locomotive.
Heavy rail
See Rail Rapid Transit.
Hertz (Hz)
The unit of acoustic or vibration frequency representing cycles per second.
Hourly average sound
level
The time -averaged A -weighted sound level, over a I -hour period, usually calculated between integral hours. Abbreviated as L(Ih).
Hybrid Bus
A rubber -tired vehicle that features a hybrid diesel-electric propulsion system. A diesel engine runs an electric generator that powers the entire vehicle including electric drive motors that deliver power to the wheels.
Idle
The speed at which an engine runs when it is not under load.
Intermediate Capacity
Transit (ICT)
A transit system with less capacity than rail rapid transit (RRT), but more capacity than typical bus operations. Examples of ICT include bus rapid transit (BRT), automated guideway transit (AGT), monorails, and trolleys.
Intermodal facility
Junction of two or more modes of transportation where transfers may occur.
Jointed rail
A system of joining rails with steel members designed to unite the abutting ends of contiguous rails.
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L(Ih)
See Hourly Average Sound Level.
Ldp
Day -Night Sound Level. The sound exposure level for a 24 -hour day calculated by adding the sound exposure level obtained during the daytime (7 a.m. to I 0 p.m.) to I 0 times the sound exposure level obtained during the nighttime (10 p.m. to 7 a.m.).
This unit is used throughout the United States for environmental impact assessment.
Also, written as DNL.
Leg('hr) time
Equivalent Sound Level. The metric for cumulative noise exposure over a specific interval is the equivalent sound level
Light Rail Transit
(LRT)
A mode of public transit with tracked vehicles in multiple units operating in mixed traffic conditions on streets as well as sections of exclusive ROW. Vehicles are generally powered by electricity from overhead lines.
Locomotive
A self-propelled, non -revenue rail vehicle designed to convert electrical or mechanical energy into tractive effort to haul railway cars. See also Power Unit.
Main line
The principal line or lines of a railway.
Maglev
Magnetically -levitated vehicle; a vehicle or train of vehicles with guidance and propulsion provided by magnetic forces. Support can be provided by either an electrodynamic system wherein a moving vehicle is lifted by magnetic forces induced in the guideway or an electromagnetic system wherein the magnetic lifting forces are actively energized in the guideway.
Maximum sound level
The highest exponential -time -average sound level, in decibels, that occurs during a stated time period. Abbreviated as Lmax. The standardized time periods are 1 second for Lmax, slow, and 0.125 second for Lm,., fast.
Metric
Measurement value or a quantitative descriptor used to identify a specific measure of sound level.
Monorail
Guided transit vehicles operating on or suspended from a single rail, beam, or tube.
Multimodal Project
In this manual, the term multimodal project is used to describe a project that includes changes to both transit and highway components in segments of the project.
Multiple Unit (MU)
A term referring to the practice of coupling two or more diesel -powered or electric - powered passenger cars together with provision for controlling the traction motors on all units from a single controller.
Noise
Any disagreeable or undesired sound or other audible disturbance.
Octave band
A standardized division of a frequency spectrum in which the interval between two divisions is a frequency ratio of 2.
One-third octave
band
A standardized division of a frequency spectrum in which the octave bands are divided into thirds for more detailed information. The interval between center frequencies is a ratio of 1.25.
Pantograph
A device for collecting current from an overhead conductor (catenary), consisting of a jointed frame held up by springs or compressed air and having a current collector at the top.
Park -and -ride facility
A parking garage and/or lot used for parking passengers' automobiles while they use transit agency facilities and vehicles.
Peak factor
See Crest factor.
Plan -and -profile
Mapping used by transportation planners that shows two-dimensional plan views (x - and y- axes) on the same page as two-dimensional profiles (x- and z-axes) of a road or track.
Peak Particle Velocity
(PPV)
The peak signal value of an oscillating vibration velocity waveform. Usually expressed in inches/second in the United States.
Peak -to -Peak (P -P)
Value
Of an oscillating quantity, the algebraic difference between the extreme values of the quantity.
Power unit
A self-propelled vehicle, running on rails and having one or more electric motors that drive the wheels and thereby propel the locomotive and train. The motors obtain electrical energy either from a rail laid near, but insulated from, the track rails, or from a wire suspended above the track. Contact with the overhead wire is made by a pantograph mounted on top of the unit.
Project segment
Portions of a project with similar characteristics.
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Pure tone
Sound of a single frequency.
Radius of curvature
A measure of the severity of a curve in a track structure based on the length of the radius of a circle that would be formed if the curve were continued.
Rail
A rolled steel shape, commonly a T -section, designed to be laid end to end in two parallel lines on cross ties or other suitable supports to form a track for railway rolling stock.
Rail Rapid Transit
(RRT)
Often called "Heavy Rail Transit." A mode of public transit with tracked vehicles in multiple units operating in exclusive rights -of -way. Trains are generally powered by electricity from a third rail alongside the track.
Receiver
A stationary far -field position at which noise or vibration levels are specified.
Relative Noise Impact
Noise increase above existing levels.
Resonance frequency
The phenomenon that occurs in a structure under conditions of forced vibration such that any change in frequency of excitation results in a decrease in response.
Right -of -Way
Abbreviated as ROW. Lands or rights used or held for railroad or transit operation.
Root Mean Square
(rms)
The square root of the mean -square value of an oscillating waveform, where the mean -square value is obtained by squaring the value of amplitudes at each instant of time and then averaging these values over the sample time.
RMS Velocity Level
(LV)
See Vibration Velocity Level.
SEL
See Sound Exposure Level.
Sound Exposure Level
The level of sound accumulated over a given time interval or event. Technically, the sound exposure level is the level of the time -integrated mean square A -weighted sound for a stated time interval or event, with a reference time of one second.
Abbreviated as SEL.
Sound
A physical disturbance in a medium that is capable of being detected by the human ear.
Spectrum
See Frequency Spectrum.
Sub -ballast
Any material of a superior character, which is spread on the finished subgrade of the roadbed and below the top -ballast, to provide better drainage, prevent upheaval by frost, and better distribute the load over the roadbed.
Subgrade
The finished surface of the roadbed below the ballast and track.
Suburban bus
A bus similar to an intercity bus with high-backed seats but no luggage compartment, often used in express mode to city centers from suburban locations.
Switch
A track structure used to divert rolling stock from one track to another.
Tangent track
Track without curvature.
Track
An assembly of rail, ties, and fastenings over which cars, locomotives, and trains are moved.
Traction motor
A specially designed direct current series -wound motor mounted on the trucks of locomotives and self-propelled cars to drive the axles.
Trainset
A group of coupled cars including at least one power unit.
Transducer
Device designed to receive an input signal of a given kind (motion, pressure, heat, etc.) and to provide an output signal of a different kind (electrical voltage, amperage, etc.) in such a manner that desired characteristics of the input signal appear in the output signal for measurement purposes.
Transfer mobility
Transfer mobility is the complex velocity response produced by a point force as a function of frequency and represents the relationship between a vibration source that excites the ground and the resulting vibration of the ground surface.
Transit center
A fixed location where passengers interchange from one route or vehicle to another.
Trolley bus
A rubber -tired, electrically -powered bus operating on city streets drawing power from overhead lines.
Truck
The complete assembly of parts including wheels, axles, bearings, side frames, bolster, brake rigging, springs, and all associated connecting components, the function of which is to provide support, mobility, and guidance to a railroad car or locomotive.
Trunk line
See Mainline. The mainline of a commuter railroad where the branch line traffic is combined.
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Turnout
An arrangement of a switch and a frog with closure rails, by means of which rolling stock may be diverted from one track to another.
VdB
See Vibration Velocity Level.
Vibration Velocity
Level (LV)
Ten times the common logarithm of the ratio of the square of the amplitude of the RMS vibration velocity to the square of the amplitude of the reference RMS vibration velocity. The reference velocity in the United States is one micro -inch per second.
Abbreviated as VdB.
Vibration
An oscillation wherein the quantity is a parameter that defines the motion of a mechanical system.
Wheel flat
A localized flat area on a steel wheel of a rail vehicle, usually caused by skidding on steel rails, causing a discontinuity in the wheel radius.
Wheel squeal
The noise produced by wheel -rail interaction, particularly on curves where the radius of curvature is smaller than allowed by the separation of the axles in a wheel set.
Additional, relevant acoustic terminology and formulas are defined in ANSI SI.I-1994 (49).
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Appendix B: Fundamentals of Noise
Noise is generally considered to be unwanted sound. Sound is what we hear when our ears are exposed to small pressure fluctuations in the air. There are many ways in which pressure fluctuations are generated, but typically they are caused by vibrating movement of a solid object. This manual uses the terms noise and sound interchangeably because there is no physical difference between them. Noise can be described in terms of three variables: amplitude (loud or soft); frequency (pitch); and time pattern (variability).
B. I Amplitude
The loudness of a sound is described by the sound wave's amplitude of pressure fluctuations above and below atmospheric pressure. Pressure is measured in Pascals. The mean value of the positive and negative pressure fluctuations is the static atmospheric pressure and is not a useful metric of sound.
However, the effective magnitude of the sound pressure in a sound wave can be expressed by the rms of the oscillating pressure. See Figure B- I for an illustration of the rms pressure.
The rms pressure is calculated according to Eq. B-1. The values of sound pressure are squared and time - averaged to smooth out variations. The rms pressure is the square root of this time -averaged value. where:
Prms
Pi
N
i=1
Prms
N
N P`
i=1
= sound pressure
= individual sound pressure
= number of samples
= index of summation
Eq. B- I
Figure B -I RMS Pressure Illustration
Most humans with typical or average hearing can perceive sounds ranging from approximately 20 microPascals to 20 million microPascals or more. Because of the difficulty in dealing with such an extreme range of numbers, acousticians use a logarithmic scale to describe sound levels. Acousticians use a compressed scale based on logarithms of the ratios of the sound energy contained in the wave related to the square of sound pressures instead of the sound pressures themselves, resulting in the "sound pressure level" in decibels (dB). The 'B' in dB is always capitalized because the unit is named after Alexander Graham Bell, a leading I 9th century innovator in communication.
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Sound pressure level (LP) is defined as:
Prms
Lp = 101og10 ( 2 ); or
Pref
where
Lp
Prms
Pref
Lp = 201og10(Prms) dB
Pref
= sound pressure level, dB
= RMS sound pressure
= 20 microPascals
Eq. B-2
Inserting the range of sound pressure values mentioned above into Eq. B-2 results in a typical quietest sound at 20 microPascals at 0 dB. A typical loudest sound of 20 million microPascals is 120 dB.
B. I. I Decibel Addition
The combination of two or more sound pressure levels at a single location requires decibel addition, which is the addition of logarithmic quantities of sound energy (Prrms).
To add sound energy from multiple, unique sources, add the sound energy as shown Eq. B-3. where
P12+P22+...+Pn2
Lp = 101oYio( 2
Pref
Lp
P1, P2,Pn
Pref
)
= sound pressure level, dB
= individual source RMS sound pressures to add
= 20 microPascals
Eq. B-3
A doubling of identical sound sources results in a 3 -dB increase, as shown mathematically below.
Lp = 101Og10 (2 PrPrms )e
f
Prms
= 10loglo ( 2 ) + 101°910 (2)
Pre f
P7 -ms
= 101ogio( 2 ) + 3
Pref
To add decibel levels (instead of sound energy) use the following equation:
where
N
Lp = 101°910(10(Lt/1o) )
i=1
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Lp
N
Li
Lp
L1, L2,Ln
= sound pressure level, dB
= number of samples
= index of summation
= individual sound pressure levels, dB
= sound pressure level, dB
= individual source sound pressure levels to add
The equation above can be rewritten as follows:
L1 L2 Ln
Lp = 10log10(1010 + 1010 + •••+ 1010) Eq. B-4
where
L1, L2,Ln = individual source sound pressure levels to add Decibel addition can be quickly approximated using Figure B-2. a)
.0
a)
O
a)
E
a)
0 C
0 0 2 4 6 8 10 12 14
Difference in Decibels
Between Two Levels To Be Added
16 Figure B-2 Graph for Approximate Decibel Addition
18 20
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Example B- I Decibel Addition — Identical Buses
Decibel Addition
What is the combined sound pressure level of two identical buses if the noise from one bus resulted in a sound pressure level of 70 dB?
Since a doubling of identical sound sources results in a 3 -dB increase:
Lp = 70+3
= 73 dB
Example B-2 Decibel Addition - Two Sources
Decibel Addition
What is the combined sound pressure level of 64 dB and 60 dB? Using Eq. B-4:
Lp = 10logio(1064/10 + 1060/10)
= 65.5 dB
Using Figure B-2:
The x-axis values represent the difference between the two sound levels, 64 and 60 dB. The difference between the sound levels in this example is 4. The point on the curve corresponding to 4 on the x-axis is 1.5. The y-axis values represent the increment that is added to the higher level.
Lp = 64 + 1.5
= 65.5 dB
B.I.2 Frequency
Sound is a fluctuation of air pressure. The number of times the fluctuation occurs in one second is called its frequency. In acoustics, frequency is quantified in cycles per second, or Hertz (Hz). The hearing for a typical human covers the frequency range from 20 Hz to 20,000 Hz.
Some sounds, like whistles, are associated with a single frequency; this type of sound is called a pure tone. However, most often, noise is made up of many frequencies, called a spectrum. Analyzing a noise spectrum allows for identification of dominant frequency ranges and can assist in identifying noise sources. Often a frequency spectrum is divided into standardized frequency bands for analysis. Most commonly, the frequency bands for transit analyses are octave bands (where the interval between two divisions is a frequency ratio of 2) and one-third octave bands (where the interval between center frequencies is a ratio of I .25).(73)
If the spectrum associated with a transit noise source is dominated by many low -frequency components, the noise will have a characteristic like the rumble of thunder; this is often associated with noise from a subway. Mid -range frequencies are often associated with wheel/rail noise, and high frequencies may be associated with wheel squeal due to sharp curves on a track.
The spectrum in Figure B-3 illustrates the full range of acoustical frequencies that can occur near a transit system. In this example, the noise spectrum was measured near a train on an elevated steel structure with a sharp curve.
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120
1/3 Octave Band Sound Pressure Level -- dB Re 20uPa
110
100
90 80
70 60
50 Rumble Roar Squeal
31.5 63 125 250 500 1000 2000 4000 8O00
ai C,
Octave Band of Transit Train on Elevated Structure -- Hz Figure B-3 Noise Spectrum of Transit Train on Curve and Elevated Structure The human auditory system does not respond equally to all frequencies of sound. For sounds normally heard in our environment, low frequencies below 250 Hz and frequencies above 10,000 Hz are generally considered less audible than the frequencies in between. This is because our ears are less sensitive in those areas. To better represent human hearing, frequency response functions were developed to characterize the way people respond to different frequencies. These are referred to as A-, B-, and C - weighted curves and represent human auditory response to normal, very loud, and extremely loud sound levels, respectively. Environmental noise is generally considered to be in the normal sound level range; and, therefore, the A -weighted sound level is considered best to represent the human response.
The A -weighting curve is shown in Figure B-4. This curve illustrates that sounds at 50 Hz would have to be amplified by 30 dB to be perceived as loud as a sound at 1000 Hz at normal sound levels. 4970
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Relative Response (dB)
10 0
-10
-20
-30
-40
-50
2 10 2 5 100 2 5 1000
Frequency (Hz)
Figure B-4 A -Weighting Curve
5 10,000
Low frequencies have longer wavelengths of sound (cycles are less frequent) and, conversely, high frequencies have shorter wavelengths (cycles are more frequent). The size of the wavelength in feet is dependent on frequency and speed of sound as follows:
where
f2 = c
f = frequency in cycles per second, Hz
A = wavelength, ft
c = speed of sound, ft/sec
Eq. B-5
The speed of sound in air varies with temperature; but at standard conditions, it is approximately 1000 ft per second. Therefore, at standard conditions, a frequency of 1000 Hz has a wavelength of I foot and a frequency of 50 Hz has a wavelength of 20 ft. The scale of these waves explains, in part, the reason humans perceive sounds of 1000 Hz better than those of 50 Hz. A wavelength of I foot is similar to the size of a person's head; whereas, a wavelength of 20 ft is similar to dimensions associated with a house, which is why low -frequency sounds (such as those from an idling locomotive) are sometimes not attenuated by walls and windows of a home. These sounds transmit indoors with relatively little reduction in strength.
B.I.3 Time Pattern
The third important characteristic of noise is its variation in time. Environmental noise is considered to be a combination of all outdoor noise sources. When combined, sources such as distant traffic, wind in trees, and distant industrial or farming activities often create a low-level background noise in which no particular individual source is identifiable. Background noise is often relatively constant from moment to moment, but varies slowly over time as natural forces change or as human activity follows its daily cycle.
In addition to this low-level, slowly varying background noise, a succession of identifiable noisy events of relatively brief duration may be added. These events may include single -vehicle passbys, aircraft flyovers, 4971
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screeching of brakes, and other short-term events, which all cause the noise level to substantially fluctuate from moment to moment.
It is possible to describe these fluctuating noises in the environment using single -number metrics to allow for manageable measurements, computations, and impact assessment. The search for adequate single -number noise metrics has encompassed hundreds of attitudinal surveys and laboratory experiments in addition to decades of practical experience with many alternative metrics.
B.I.4 Noise Metrics
The noise metrics referred to in this manual are described in the sections below.
B. I.4. I A -weighted Sound Level: The Basic Noise Unit The basic noise unit for transit noise is the A -weighted sound level and is described in ANSI S1.1-1994 (49). It describes the noise level at the receiver at any moment in time and can be read directly from noise -monitoring equipment when frequency weighting is set to A -weighting. Figure B-5 shows examples of typical A -weighted sound levels for both transit and non -transit sources, ranging from approximately 30 dBA (very quiet) to 90 dBA (very loud).
The unit dBA denotes the decibel level is A -weighted. The letter "A" indicates that the sound has been filtered to reduce the strength of very low and very high -frequency sounds to emulate the human response to sound levels as described in Appendix B. I.2. This allows for events that are out of the range of human hearing, such as high -frequency dog whistles and low -frequency seismic disturbances, to be filtered out. On average, each A -weighted sound level increase of I 0 dB corresponds to an approximate doubling of subjective loudness.
A -weighted sound levels are adopted as the basic noise unit for transit noise impact assessments because they:
• Can be measured easily,
• Approximate the human ear's sensitivity to sounds of different frequencies, • Match attitudinal -survey tests of annoyance better than other basic units, • Have been in use since the early 1930s, and
• Are endorsed as the proper basic unit for environmental noise by most agencies concerned with community noise throughout the world.
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Transit Sources
Rail Transit on Old Steel Structure.
50 mph
Rail Transit Horn
Rail Transit on Modern Concrete
Aerial Structure. 50 mph
Rail Transit At -Grade. 50 rapt;,
City Pus. Riling
Rail Transit in Station
All at 50 t1
dBA Non -Transit Sources
Outdoor Indoor
Rock Drill
Jack Hammer
Concrete Mixer
Alr Compressor
Lawn Mower
Lawn Tiller
Air Cond toner
All at 50 fl
Figure B-5 Typical A -weighted Sound Levels
Shop Tools, In use
Shop Tools. Idling
Food Blender
Clothes Washer
Air Conditioner
Refrigerator
All at 3 tt
B. I.4.2 Maximum Sound Level (Lm,x) During a Single Noise Event As a transit vehicle approaches, passes by, and then recedes into the distance, the A -weighted sound level rises, reaches a maximum, and then fades into the background noise. The maximum A -weighted sound level reached during this passby is called the maximum sound level, (49) abbreviated here as Lmax.
Lmax is illustrated in Figure B-6 where time is plotted horizontally, and A -weighted sound level is plotted vertically.
Although Lora,, is commonly used in vehicle -noise specifications,xvi it is not used for transit environmental noise impact assessment. Lma, does not include the number and duration of transit events, which are important for assessing people's reactions to noise. It also cannot be normalized to a one -hour or 24 -hour cumulative measure of impact, and therefore, is not conducive to comparison among different transportation modes. For example, cumulative noise metrics commonly used in highway noise assessments are Leq(Ihr) and L10, the noise level exceeded for '0 percent of the peak hour. xv, For noise compliance tests of transient sources, such as moving transit vehicles under controlled conditions with smooth wheel and rail conditions, Lmax is typically measured with the sound level meter's time weighting set to "fast." However, for tests of continuous or stationary transit sources, it is usually more appropriate to use the "slow" setting. When set to "slow," sound level meters ignore some of the very -transient fluctuations, which are negligible when assessing the overall noise level.
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.r 90 _
cn
V
ai
a.)
a 80
U)
V
a)
a)
i 70 _
0 Lmax = 88
SEL-89.6
4 8 12 16 20 24 28 Seconds
Figure B-6 Typical Transit -Vehicle Passby
B. I.4.3 Sound Exposure Level (SEL): Exposure from a Single Noise Event
Sound exposure level, abbreviated here as SEL, is the cumulative noise exposure from a single noise event, normalized to one second (49). SEL contains the same overall sound energy as the actual varying sound energy during the event. It is the primary metric for the measurement of transit vehicle noise emissions and an intermediate metric in the measurement and calculation of both Leq(Ihr) and Ldp. The SEL metric is A -weighted and is expressed in the unit dBA.
This concept is illustrated in Figure B-6 and Figure B-7 where the shaded regions are the sound exposure during and event. The example in Figure B-6 is a transit -vehicle passby and Figure B-7 is an example of a fixed -transit facility as a transit bus is started, warmed up, and then driven away. For this event, the noise exposure is large due to duration of the event.
SEL is an A -weighted cumulative measure that is referenced to one second. Louder events have greater SELs than quieter events, and events of longer duration have greater SELs than shorter events. This is generally consistent with community response to noise. Noise events of longer duration are considered more disruptive than events of shorter duration with equal maximum A -weighted sound levels.
A -Weighted Sound Level, dBA
90 80
70 _
0 SEL = 89.6
Lmax = 82
ifliPVAMIV 41/11\
8 12 16 20 24 28 Seconds
Figure B-7 Typical Fixed -Facility Noise Event
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Conceptually, the sound exposure level can be expressed as:
SEL = 101og10(Total sound energy )
during the event
Mathematically, the sound exposure level is computed as follows:
N
where
SEL = 101°910(11 0(Li/10) )
SEL
N
Li
i=1
= Sound exposure level, dBA
= number of samples
= index of summation
= individual A -weighted sound level, dBA
Eq. B-6
The events shown in Figure B-6 and Figure B-7 are compared graphically in Figure B-8 using a logarithmic vertical scale. The shaded zones in these figures indicate noise exposure over time. The actual event shows the noise exposure over the time of the event, and the equivalent SEL shows the total noise exposure normalized to one second. Note that events I and 2 in Figure B-8 have different time periods and noise levels throughout the event, but the same resulting SEL.
SEL is used in transit noise analyses because it:
I. Accounts for both the duration and amplitude of an event,
2. Allows a uniform assessment method for both transit -vehicle passbys and fixed -facility noise events, and
3. Can be used to calculate the one -hour and 24 -hour cumulative metrics for comparison across different transportation modes.
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A -Weighted Sound Level, d8A
o
85 80
75 Zero Energy 70
Event 1: Loud Noise for
Event 2: Lower Maximum Level
Short Duration for Longer Duration
Squeezed SEL
Actual Event
Squeezed SEL
Actual Event
0 4 8 12 16 20 24 — 'r— 0 4 8 12 16 20 24
Time Axis 1 sec.
Figure B-8 An Energy View of Noise
B. I.4.4 Equivalent Sound Level (Leq(t))
Time Axis 1 sec.
Events
The metric for cumulative noise exposure over a specific time interval is the equivalent sound level (49).
It is a single decibel value that accounts for total sound energy from all sound levels over a specified time interval (or time period). The time period associated with the equivalent sound level metric can vary for different types of analyses. This metric is abbreviated as Leq(c), where "t" is the duration of the time period. Leq(,) represents a hypothetical constant sound level and contains the same overall sound energy as the actual varying sound energy during the time period "t". For most transit noise analyses, an A - weighted, hourly equivalent sound level is used, abbreviated here as Leq(Ihr). Leq(Ihr) is expressed in the unit, dBA.
Figure B-9 shows examples of typical unmitigated hourly Leq(Ihr) 's, both for transit and non -transit sources ranging from 40 (quiet) to 80 dB (loud). Note that these Leq(Ihr) 's depend upon both the number of events during the hour as well as each event's duration, which is affected by vehicle speed. For example, doubling the number of events during the hour will increase the Leq( I hr) by 3 decibels, as will doubling the duration of each individual event.
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Transit Sources Lpr, Non -Transit Sources
Commuter Trains at 50 mph,
6 per Hour with Horn Blowing —I"
Commuter Trains al 50 mph
6 per Hour
Rail Transit Trains at 40 mph
12 per Hour
Rail Transit Trains at 20 mph
12 per Hour
All at 50 ft
10 90
&0
70 60
50 40
— 8 -Lane Highway
- 6 -Lane Highway
.— 4 -Lane Urban Arterial Road
-4— 2 -Lane Suburban Arterial Road
All at 50 ft
Figure B-9 Typical Hourly Leg(' hr)
An example of sound levels over time for a single noise event such as a train passing on nearby tracks is illustrated in the top frame of Figure B- I O. As the train approaches, passes by, and then recedes into the distance, the A -weighted sound level rises, reaches a maximum, and then fades into the background noise. The equivalent sound level is shown for three different time periods Figure B -I O. The area under the curve in this top frame is the noise that reaches the receiver (noise exposure) over this five-minute period. The center frame of the figure shows sound levels over the one -hour period, including the five- minute period from the top frame. The area under the curve represents the noise exposure for one hour. The bottom frame shows sound levels over a full 24 -hour period and is discussed in Appendix B.I.4.5.
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5 Minutes
00 85 a-
80 -
4 75
-70
Uy
c�
55 50
Sound Level, dBA
45 -
40 Lmax (86 dBA)
Leq (5 min) = 65 dBA
Leq(1 sec)
► ➢ 1 I-➢ t r I r 1 +
1525 . - 15:26 15:27 15:28 15:29
90 15 30
1 Hour
85 1
75 -
70 -
65 60
45 -
Leq(1 hr) = 61 dBA
50 40 '.: .
15:00 _ 137T.>--. _15:10
0000
02:00
04:00
15:15
"5:23
Leq(5 sec)
}
5:25 15.30 15:35 15:40 15:45 15:50 155,�.�' 10:00.
24 Hours
Ldn = 62 dBA
Leq(24 hr) = 57 dBA
06:00 06:00 10 00 12:00 14.30 18:30 0:00 213:00 22:00 240)1 Typical A -weighted Sound Level Variation over a 24 -Hour Period Figure B-10 Example A -weighted Sound Level Time Histories Conceptually, the equivalent sound level can be expressed as:
Total Sound Energy
Leq(t) = 101Og10( Time Period )
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Mathematically, the equation is as follows:
N
Leq(t) = 1010 1I 10(Lt/1o))
91o(T
i=1
where
Leq(t)
T
N
Li
= equivalent sound level of time period "t", dBA
= time period, sec (3600 for an hourly Leq(Ihr))
= number of samples, sec (3600 for an hourly Leq(Ihr))
= index of summation
= individual A -weighted sound level, dBA
The equation above can be rewritten as follows for a one -hour time period:
Lea(1h) = 101og10[Total Sound Energy in 1 hr] — 35.6
where
35.6 = numerical adjustment for a time period of I hour (I Ologio(t)) Eq. B-7
The sound energy is totaled over a full hour (3600 seconds) and is accumulated for all noise events during that hour. When computing the equivalent sound level for a time period other than one hour, T is modified in the equation to the duration of the time period in seconds. The numerical adjustment (35.6) accounts for time period of interest, in this case, one hour.
An alternate way for computing Leq(Ihr)for a series of transit -noise events using sound exposure levels can be expressed conceptually as follows:
L Energy Sum of ) 35.6
eq (1h ) = 1010 910 ( all SELs
Mathematically, the equation is as follows:
where
N
Leq(t) = 101ogio(- 10(set,i/10))
T
i=1
Leq(t)
T
N
SEL
= equivalent sound level of time period "t", dBA
= time period, sec (3600 for an hourly Leq(Ihr))
= number of sample, sec (3600 for an hourly Leq(Ihr))
= index of summation
= individual sound exposure level, dBA
Eq. B-8
Hourly Leq(Ihr) is adopted as the measure of cumulative noise impact for non-residential land uses (those not involving sleep) because Leq(Ihr):
• Correlates well with speech interference in conversation and on the telephone — as well as interruption of TV, radio, and music enjoyment;
• Increases with the duration of transit events;
• Accounts for the number of transit events over the hour, which is also important to people's reactions; and
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■ Is used by the Federal Highway Administration in assessing highway -traffic noise impact.(Thus, this noise metric can be used for directly comparing and contrasting highway, transit, and multimodal alternatives).
B. I.4.5 Day -Night Sound Level (Ldn): 24 -Hour Exposure from All Events
The metric for cumulative 24 -hour exposure is the Day -Night Sound Level, (49) abbreviated here as Ldn.
It is a single, A -weighted decibel value that accounts for total sound energy from all sound sources over 24 hours and is expressed in the unit, dBA. Events between I O p.m. and 7 a.m. are increased by I O dB to account for people's greater nighttime sensitivity to noise.
Figure B- I I shows examples of typical Ldn's, both for transit and non -transit sources, ranging from 50 to 80 dB, where 50 is considered a quiet 24 -hour period and 80 a loud 24 -hour period. Note that these Ldn's depend upon the number of events during day and night separately, including each event's duration, which is affected by vehicle speed.
Transit Sources
Commuter Train with Horn at 40 mph
Loco + 8 Cars
15 Day, 3 Night
Rail Transit at 40 mph
6 -Car Trains
30O Day, 18 Night
Commuter Train at 40 mph
Loco + 8 Cars
15 Day, 3 Night
Rail Transit at 20 mph
2 -Car Trains
300 Day, 18 Night
All at50ft
Lin Background Noise
D
90 80
70 50
40 - Downtown City
- "Very Noisy" Urban Residential Area
"Quiet" Urban Residential Area
Suburban Residential Area
Small Town Residential Area
Figure B- I I Typical Ldn's
An example of sound level variation over 24 hours is visualized in the bottom frame of Figure B- I O. The area under the curve represents the receiver's noise exposure over the 24 hours. Note that some vehicle passbys occur at night, when the background noise is typically lower and the I O dB adjustment is applied.
Conceptually, the day -night level can be expressed as:
Total Sound EnergyDay nadj,n x Total Sound EnergyNiyht
Ldn = 1010-10(Time PeriodDay (seconds) + Time PeriodNiynr (seconds) 4980
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Mathematically, the equation is as follows:
N M
Ldn = 10109100 ti x 10(Ld,t/10) + tj x 10((Ln,j+nadjn)/1o)) Td i=1 Tn j=1
where
Ldn
Td
N
ti
Tn
M
j
tj
Ln,1
nad j,n
= cumulative 24 -hour exposure (day -night sound level), dBA = time period during the daytime, between 7 a.m. and 10 p.m. sec (54,000) = number of samples during the daytime (54,000)
= index of summation
= time interval of measurements in seconds (I)
= individual A -weighted sound level during the daytime, dBA = time period during the nighttime, between I O p.m. and 7 p.m. sec (32,400) = number of samples during the nighttime (32,400)
= index of summation
= time interval of measurements, sec (I)
= individual A -weighted sound level during the nighttime, dBA = nighttime noise adjustment (I0 dB)
The equation above can be rewritten as follows:
Ldn = 10loglo[ (15 * Total Sound Energyoay) + (9 * nadj,n * Total Sound EnergyNtyht)] — 49.4 Eq. B-9
The sound energy is totaled over a full 24 hours, and the sound energy is accumulated from all noise events during that time period. The numerical adjustment (49.4) accounts for time period of interest, in this case, 24 hours.
An alternative way of computing Ldp from twenty-four hourly Leq(Ihr) 's can be expressed conceptually as follows:
Energy sum of Energy sum of
daytime, hourly Legs + (nadj,n * nighttime, hourly Legs) Ldn = 101og10( Time period (seconds) )
The equation above can be rewritten as:
Energy sum of Energy sum of
daytime, hourly Legs + (nadj,n * nighttime, hourly Legs) Ldn = 101og10( 86400
(3600)
The equation above can be reduced further and rewritten as:
L — 1010 Energy sum of + n * Energy sum of 13.8
Ldn — -1o(daytime, hourly Legs ( adj,n nighttime, hourly Legs)) Eq. B- I 0
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Ldn due to a series of transit -noise events can also be computed in terms of SEL. The equation below assumes that transit noise dominates the 24 -hour noise environment, where nighttime SELs are increased by I O dB before totaling:
L 10lo = Energy sum of + n * Energy sum of 49.4
dn. glo(all daytime SELs ( adj,n all nighttime SELs--
Eq. B- I I
Ldn is adopted as the measure of cumulative noise impact for residential land uses (those involving sleep), because it:
• Correlates well with the results of attitudinal surveys of residential noise impact • Increases with the duration of transit events
• Accounts for the number of transit events over the full twenty-four hours ■ Accounts for the increased sensitivity to noise at night, when most people are asleep ■ Allows composite measurements to capture all sources of community noise combined • Allow quantitative comparison of transit noise with other community noises • Is the designated metric of choice of other Federal agencies (e.g., HUD, FAA, and EPA) and has wide international acceptance
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Appendix C: Background for Transit Noise Impact
Criteria
The noise criteria presented in Section 4. I of this manual have been developed based on well - documented criteria and research on human response to community noise. The primary goals in developing the noise criteria were to ensure that the impact limits are firmly founded in scientific studies, realistically based on noise levels associated with new transit projects, and represent a reasonable balance between community benefit and project costs. This appendix provides background information on the development of these criteria.
C. I Relevant Literature
The following is an annotated list of the documents that are particularly relevant to the noise impact criteria:
I. U.S. EPA's "Levels Document"(74)
This report identifies noise levels consistent with the protection of public health and welfare against hearing loss, annoyance, and activity interference. It has been used as the basis of numerous community noise standards and ordinances.
2. Committee on Hearing, Bioacoustics and Biomechanics (CHABA) Working Group 69, "Guidelines for Preparing Environmental Impact Statements on Noise"(75) This report was the result of deliberations by a group of leading acoustical scientists with the goal of developing a uniform national method for noise impact assessment. Although the CHABA's proposed approach has not been adopted, the report serves as an excellent resource documenting research in noise effects. It provides a strong scientific basis for quantifying impacts in terms of Ldn.
3. American Public Transportation Association (APTA) Guidelines for Design of Rapid Transit Facilities(76)
The noise and vibration sections of the APTA Guidelines have been used successfully in the past for the design of rail transit facilities. The APTA Guidelines include criteria for acceptable community noise and vibration. Experience has shown that meeting the APTA Guidelines will usually result in acceptable noise levels; but the metric used in the APTA Guidelines is not appropriate for environmental assessment purposes.
The APTA Guidelines criteria are in terms of Lmax for conventional RRT vehicles, and they cannot be used to compare among different modes of transit. Since the APTA Guidelines are expressed in terms of maximum passby noise, they are not sensitive to the frequency or duration of noise events for transit modes other than conventional RRT operations with 5 to 10 minute headways. Therefore, the APTA criteria are questionable for assessing the noise impact of other transit modes that differ from conventional rapid transit with respect to source emission levels and operating characteristics (e.g., commuter rail, AGT, and a variety of bus projects).
4. Synthesis of Social Surveys on Noise Annoyance(77)
In 1978, Theodore J. Schultz, an internationally known acoustical scientist, synthesized the results of a large number of social surveys concerning annoyance due to transportation noise. A group of these surveys were remarkably consistent, and the author proposed that their average FEDERAL TRANSIT ADMINISTRATION 217
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results be taken as the best available prediction of transportation noise annoyance. This synthesis has received essentially unanimous acceptance by acoustical scientists and engineers.
The "universal" transportation response curve developed by Schultz (Figure 3-7) shows that the percent of the population highly annoyed by transportation noise increases from zero at an Ldn of approximately 50 dBA to 100% when Ldn is approximately 90 dBA. Most importantly, this curve indicates that for the same increase in Ld", there is a greater increase in the number of people highly annoyed at high noise levels than at low noise levels. For example, a 5 dB increase at low ambient levels (40 - 50 dB) has less impact than at higher ambient levels (65 - 75 dB). A recent update of the original research containing several railroad, transit, and street traffic noise surveys, confirming the shape of the original Schultz curve (12).
5. HUD's Standards(19)
HUD has developed noise standards, criteria, and guidelines to ensure that housing projects supported by HUD achieve the goal of a suitable living environment. The HUD acceptability standards define 65 dB (Ldn) as the threshold for a normally unacceptable living environment (moderate impact for FTA) and 75 dB (Ldn) as the threshold for an unacceptable living environment (severe impact for FTA).
C.2 Basis for Noise Impact Criteria Curves
The lower curve in Figure 4-2 represents the onset of moderate impact and is based on the following considerations:
• The EPA finding that a community noise level of Ldn less than or equal to 55 dBA is "requisite to protect public health and welfare with an adequate margin of safety."(72) ■ The conclusion by EPA and others that a 5 dB increase in Ldn or Leq(Ihr) is the minimum required for a change in community reaction.
• The research concludes that there are very few people highly annoyed when the Ldn is 50 dBA, and that an increase in Ldn from 50 dBA to 55 dBA results in an average of 2% more people highly annoyed (Figure 3-7).
The increase in noise level from an existing ambient level of 50 dBA to a cumulative level of 55 dBA because of a project is found to cause minimal impact, with 2% of people highly annoyed, as described in the bullets above. This is considered the lowest threshold where impact starts to occur. Therefore, for an existing ambient noise level of 50 dBA, the curve representing the onset of moderate impact is at 53 dBA, the combination of which yields a cumulative level of 55 dBA by decibel addition. The remainder of the lower curve in Figure 4-2 was determined from the annoyance curve (Figure 3-7) by allowing a fixed 2% increase in annoyance at other levels of existing ambient noise. As cumulative noise increases, the increment to attain the same 2% increase in highly annoyed people is smaller. While it takes a 5 -dB noise increase to cause a 2% increase in highly annoyed people at an existing ambient noise level of 50 dB, an increase of only I dB causes a 2% increase of highly annoyed people at an existing ambient noise level of 70 dBA.
The upper curve in Figure 4-2 represents the onset of severe impact based on a total noise level, corresponding to a higher degree of impact. The severe noise impact curve is based on the following considerations:
• HUD defines an Ldn of 65 as the onset of a normally unacceptable noise zone (moderate impact for FTA) in its environmental noise standards (19). FAA considers that residential land uses are not compatible with noise environments where Ldn is greater than 65 dBA (20). 4984
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■ An increase of 5 dB in Ldn or Leq(t) is commonly assumed as the minimum required increase for a change in community reaction.
■ The research concludes that an increase of 5 dB in Ldn or Le(*) represents a 6.5% increase in the number of people highly annoyed (Figure 3-7).
The increase in noise level from an existing ambient level of 60 dBA to a cumulative level of 65 dBA caused by a project represents a change from an acceptable noise environment to the threshold of an unacceptable noise environment. This is considered the level at which severe impact starts to occur with a 6.5% increase in the number of people highly annoyed as described in the bullets above.
Therefore, for an existing ambient noise level of 60 dBA, the curve representing the onset of severe impact is at 63 dBA, the combination of which yields a cumulative level of 65 dBA by decibel addition.
The remainder of the upper curve in Figure 4-2 was determined from the annoyance curve (Figure 3-7) by allowing a fixed increase of the 6.5% increase in annoyance at all existing ambient noise levels.
Both curves incorporate a maximum limit for the transit project noise in noise -sensitive areas.
Independent of existing noise levels, moderate impact for land use categories I and 2 is considered to occur whenever the transit Ldn equals or exceeds 65 dBA, and severe impact occurs whenever the transit Ldn equals or exceeds 75 dBA. These absolute limits are intended to restrict activity interference caused by the transit project alone.
Both curves also incorporate a maximum limit for cumulative noise increase at low existing noise levels (below approximately 45 dBA). This is a conservative limit that reflects the lack of social survey data on people's reactions to noise at such low ambient levels. Like the FHWA approach in assessing the relative impact of a highway project, the transit noise criteria include limits on noise increase of I 0 dB and 15 dB for moderate impact and severe impact, respectively, relative to the existing noise level.
Note that due to the types of land use included in category 3, the criteria allow the project noise for category 3 sites to be 5 dB greater than for category I and category 2 sites. This difference is reflected by the offset in the vertical scale on the right side of Figure 4-2. Aside from active parks, which are clearly less sensitive to noise than category I and 2 sites, category 3 sites include primarily indoor activities. Therefore, the criteria account for some noise reduction from the building structure.
C.3 Equations for Noise Impact Criteria Curves
The equations for the noise impact criteria curves shown in Figure 4-2 are included in this section.
These equations may be useful when performing the noise assessment methodology using spreadsheets, computer programs, or other analysis tools. Otherwise, such mathematical detail is generally not necessary to implement the criteria, and direct use of Figure 4-2 is adequate and less time-consuming.
A total of four continuous curves are included in the criteria, creating two threshold curves for moderate and severe impact for category I and 2, and two curves for category 3 (See Table C- I ). Note that for each level of impact, the overall curves for categories I and 2 are offset by 5 dB from category
3. While each curve is graphically continuous, each one is defined by a set of three discrete equations.
These equations are approximately continuous at the transition points. The following is a description of the three equations:
■ The first equation in each set is a linear relationship, representing the portion of the curve in which the existing noise exposure is low, and the allowable increase is limited to 10 dB and 15 dB for moderate impact and severe impact, respectively.
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• The second equation in each set represents the impact threshold over the range of existing noise exposure for which a fixed percentage of increase in annoyance is allowed, as described in Appendix C.2. This curve is a third -order, polynomial approximation derived from the Schultz curve(75) and covers the range of noise exposure encountered in most populated areas. This curve is used for determining noise impact in most cases for transit projects. • The third equation represents the absolute limit of project noise imposed by the criteria for areas with high existing noise exposure. For land use category I and 2, the absolute limit is 65 dBA for moderate impact and 70 dBA for severe impact. For land use category 3, the absolute limit is 75 dBA for moderate impact and 80 dBA for severe impact.
Table C -I Threshold of Moderate and Severe Impacts
Threshold of Moderate Impact
Category I and 2
Category 3
11.450 + 0.953LE, LE 71
16.450 + 0.953LE, LE 71
Eq. C- 12
Eq. C- 13
Threshold of Severe Impact
Category I and 2
17.322 + 0.940LE, LE 77
Category 3
22.322 + 0.940LE, LE 77
Eq. C- 14
Eq. C- 15
LE = the existing noise exposure in terms of Lan or Leq(Ihr) [p = the project noise exposure which determines impact in terms of Ldn or Leq(Ihr)) 4986
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Appendix D: Clustering Receivers of Interest
This appendix supplements the information in Section 4.5 on clustering receivers of interest.
The general approach to selecting noise -sensitive receivers in the study area is included in Section 4.5, Step I. General guidelines are as follows:
• Select the following types of receivers to evaluate individually:
▪ Every major noise -sensitive public building
▪ Every isolated residence
▪ Every relatively small outdoor noise -sensitive area
• Residential neighborhoods and relatively large outdoor noise -sensitive areas can often be clustered and represented by a single receiver.
Clustering similar receivers reduces the number of computations needed later, especially for large-scale projects where a greater number of noise -sensitive sites may be affected. For this approach to be effective, it is essential that the representative receiver accurately represents the noise environment of the cluster.
The major steps in clustering receivers include:
I. First, cluster receivers according to approximately equal exposure to the primary project noise source. These areas typically run parallel to a linear project or circle major stationary sources relative to the proposed project.
2. Next, cluster receivers according to major sources of ambient noise. These areas typically run parallel to or encircle major sources of ambient noise.
3. Then, cluster receivers according to changes in the project layout or operations along the corridor.
4. Finally, select a representative receiver for each cluster.
The major steps are expanded below and include instructions on how to draw cluster boundaries on a map.
I. Boundaries along the proposed project — Draw cluster boundaries along the proposed project as described below to separate clusters based on distance from the project. Draw these cluster boundaries for the project sources listed as major in Table 4-19.
Within both residential and noise -sensitive outdoor areas:
■ Primary project source
Draw cluster boundaries at the following distances from the near edge of the primary project source: 0 ft, 50 ft, 100 ft, 200 ft, 400 ft, and 800 ft. For linear sources, such as a rail line, draw these boundaries as lines parallel to the proposed ROW line. For stationary sources, draw these boundaries as approximate circles around the source, starting at the property line.
Do not extend boundaries beyond the noise study area, identified in the Noise Screening Procedure in Section 4.3 or the General Noise Assessment of Section 4.4. 4987
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• Remaining project sources — Repeat the process for the primary project source for all other project listed as major in Table 4-19, such as substations and crossing signals. If several project sources are located approximately together, only consider one source, since the others would produce approximately the same boundary.
It is good practice to optimize the number of clusters for a project to simplify the procedure.
Where rows of buildings parallel the transit corridor:
• Ensure that cluster boundaries fall between the following rows of buildings, counting back away from the proposed project:
▪ Between rows I and 2
• Between rows 2 and 3
• Between rows 3 and 4
• Add cluster boundaries between these rows if not already included.
2. Boundaries along sources of ambient noise — Draw cluster boundaries along all major sources of ambient noise based upon distance from these sources, as described below. • Draw cluster boundaries along all interstates and major roadway arterials at the following distances from the near edge of the roadway: 0 ft, I00 ft, 200 ft, and 500 ft. • Draw cluster boundaries along all other roadways that have state or county numbering at 0 ft and 100 ft from the near edge of the roadway.
• For all major industrial sources of noise, draw cluster boundaries that encircle the source at the following distances from the near property line of the source: 0 ft, 100 ft, 200 ft, and 400 ft.
3. Boundaries based on changes in project layout or operations — Further subdivision is needed to account for changes in project noise where proposed project layout or operating conditions change considerably along the corridor. Draw a cluster boundary perpendicular to the corridor extending straight outward to both sides at the following locations:
• Where parallel tracks previously separated by more than approximately 100 ft are moved closer together
• Approximately where speed and/or throttle are reduced when approaching stations and where steady service speed is reached after departing stations • Approximately 200 ft up and down the line from grade crossing bells • At transitions from jointed to welded rail
• At transitions from one type of cross section to another including on structure, on fill, at -grade and in cut
• At transitions from open terrain to heavily wooded terrain • At transitions between areas free of locomotive horn noise and areas subject to this noise source
• Any other positions along the line where project noise is expected to change considerably, such as up and down the line from tight curves where wheels may squeal
4. Selection of a representative receiver from each cluster — Determine a representative receiver for each cluster boundary drawn in the steps above. • Residential clusters
Select a representative receiver within the cluster at the house closest to the proposed project.
If this receiver is not the clear choice, select the receiver furthest from major sources of ambient noise.
• Outdoor noise -sensitive clusters (e.g., urban park or amphitheater) 4988
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Select a representative receiver within the cluster at the closest point of active noise -sensitive use. If this receiver is not the clear choice, select the receiver farther from major sources of ambient noise.
Note that some clusters may fall between areas with receivers of interest. This could occur when operational changes or track layouts change in an open, undeveloped area. Retain these clusters. Do not merge them with adjacent clusters. Do not select a representative receiver of interest from them.
Example D- I Clustering Receivers
Receivers of Interest and Clustering Receivers
In this hypothetical situation, a new rail transit line, labeled "new rail line" in Figure D -I, is proposed along a major urban street with commercial land use. A residential area is located adjacent to the commercial strip, located approximately one-half block from the proposed transit alignment. A major arterial, labeled "highway," crosses the alignment.
Cluster Receivers Along the Primary Project Source
Primary Project Source
The primary project source in this example is the new rail line. Boundaries are first drawn at distances of 0 ft from the right -of- way line (edge of the street in this example), 50 ft, 100 ft, 200 ft, 400 ft, and 800 ft, (Figure D -I).
Distances are labeled at the top of the figure.
This is proposed to be a constant speed section of track, so there are no changes in boundaries due to changes in operations along the corridor. Moreover, no other project sources are shown here, but if there had been a station with a parking lot, lines would have been drawn enveloping the station site at the specified distances from the property line.
Rows of Buildings Parallel to the Transit Corridor
This example includes rows of buildings parallel to the transit corridor. The first set of boundary lines satisfies the requirement that cluster boundaries fall between rows I and 2, and between rows 2 and 3, but there is no line between rows 4 and 5. Consequently, a cluster boundary labeled "R" at the top of the figure has been drawn between the 4th and 5th row of buildings.
Cluster Receivers Along the Primary Project Source
The roadway arterial (labeled "highway") is the only major source of ambient noise shown.
Cluster boundaries are drawn at 0 ft, 100 ft, 200 ft and 500 ft from the near edge of the roadway on both sides.
These lines are shown with distances labeled at the side of the figure.
Select a Representative Receiver from Each Cluster
Representative receivers are shown as filled circles in Figure D -I. Note that the receivers labeled with "REC" are primarily for use in Appendix E.
Locate receiver, "REC 3". Note that this cluster is located at the outer edge of influence from the major source ("highway") where local street traffic is the dominant source for ambient noise (in practice, this would be verified by a measurement).
"REC 3" is chosen to represent this cluster because it is among the houses closest to the proposed project source in this cluster and it is in the middle of the block affected by the dominant local street. Ambient noise levels at one end of the cluster may be influenced more by the highway and the other end may be affected more by the cross street, but the majority of the cluster would be represented by receiver site "REC 3." FEDERAL TRANSIT ADMINISTRATION 223
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r RECEIVERS OF INTEREST
CLUSTER BOUNDARIES
ROADWAY (AMBIENT)
RAIL (PROJECT)
AEC N RECEIVER EXAMPLE
CLUSTER EXAMPLE
SCALE IN FEET
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Appendix E: Determining Existing Noise
Different options of determining existing noise, including full measurement, computation from partial measurements, and tabular look -up, are described in Section 4.5, Step 5. This appendix provides additional details associated with each method and examples of when each method could be used.
Additional details on the methods for estimating existing noise are provided below:
Option I: Leq(Ihr) measurement (non-residential) — Full one -hour measurements are recommended to determine existing noise for non-residential receivers of interest. These measurements are preferred over all other options and will accurately represent the Leq(Ihr). The following procedures apply to these full -duration measurements:
■ Measure Leq(Ihr) at the receiver of interest during a typical hour of use on two non -successive days. Choose the hour in which maximum project activity will occur. The Leq(Ihr) will be accurately represented using this method. Typically, measuring between noon Monday and noon Friday is recommended, but weekend days may be more appropriate for places of worship. ■ Position the measurement microphone for all sites as shown in Figure 4-19, considering relative orientation of project and ambient sources. Position the microphone in a location that is somewhat shielded from the ambient source to measure the ambient noise at these locations at the quietest area on the property.
■ Conduct all measurements in accordance with good engineering practice.
Option 2: Ldn measurement (residential) — Full 24 -hour measurements are recommended to determine ambient noise for residential receivers of interest. These measurements are preferred over all other options and will accurately represent the Ldn• The following procedures apply to these full - duration measurements:
■ Measure a full 24 -hour Ldn at the receiver of interest for a single weekday (generally between noon Monday and noon Friday).
■ Position the measurement microphone for all sites as shown in Figure 4-I9 considering relative orientation of project and ambient sources. Position the microphone in a location that is somewhat shielded from the ambient source to measure the ambient noise at these locations at the quietest area on the property.
■ Conduct all measurements in accordance with good engineering practice.
Option 3: La„ computation of Ldn from 3 partial Leq(Ihr) measurements (residential) — An alternative way to determine Ldn is to measure Leq(Ihr) for three typical hours of the day, then compute the Ldn from these three Leq(Ihr) measurements. This method is less precise than its full -duration measurement. The following procedures apply to this partial -duration measurement method for Ldn:
■ Measure the Leq(Ihr) during each of the following time periods:
• During peak -hour roadway traffic
▪ Midday, between the morning and afternoon roadway -traffic peak hours ▪ During late night between midnight and 5 a.m.
■ Position the measurement microphone for all sites as shown in Figure 4-I9 considering relative orientation of project and ambient sources. Position the microphone in a location that is somewhat shielded from the ambient source to measure the ambient noise at these locations at the quietest area on the property.
■ Conduct all measurements in accordance with good engineering practice. ■ Compute the Ldn using the equation below
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Leq.peakhour•-2 Leq. midday -2 Leq.latenight+8 Eq. E- I Ldn 101og(3 x 10 10 + 12 x 10 10 + 9 x 10 10 ) — 13.8
The resulting Ldn will be slightly underestimated due to the adjustment to the measured levels in these equations. This underestimation is intended to compensate for the reduced precision of the computed Ldn. If using this method, a minimum time duration of one hour should be used for each measurement period in computing an Ldn.
Option 4: Computation of Lan from I partial Leq(Ihr) measurement (residential) — Lan can also be determined by measuring Leq(Ihr) for one hour of the day, and then computing Ldn from the Leq( Ihr)• This method is less precise than computing Ldn from 3 Leg(' ht-) measurements. This method may be useful for projects with are many sites assessed by the General Noise Assessment. This method may also be appropriate when determining if a particular receiver of interest represents a cluster in a Detailed Noise Analysis. The following procedures apply to this partial -duration measurement option for Ldn:
■ Measure the Leq(Ihr) for the loudest hour of project -related activity during hours of noise sensitivity. If this hour is not selected, other hours may be used with the understanding that the estimate is less precise.
■ Position the measurement microphone for all sites as shown in Figure 4-I9, considering relative orientation of project and ambient sources. Position the microphone in a location that is somewhat shielded from the ambient source to measure the ambient noise at these locations at the quietest area on the property.
■ Conduct all measurements in accordance with good engineering practice. ■ Convert the measured hourly Leq(Ihr) to Ldn with the appropriate equation below.
For measurements between 7 a.m. and 7 p.m.:
Ldn s Leq — 2
For measurements between 7 p.m. and 10 p.m.:
Ldn Leq + 3
For measurements between I0 p.m. and 7 a.m.:
Ldn Leq + 8
Eq. E-2
Eq. E-3
Eq. E-4
The resulting Ldn will be moderately underestimated due to the use of the adjustment constants in these equations. This underestimation is intended to compensate for the reduced precision of the computed Ldn. If using this method, a minimum time duration of one hour should be used for each measurement period in computing an Ldn.
Option 5: Computation of Leg('hr)or Ldn from Leg('hr)or Ldn of a comparable site (all land uses) — Computing Leq(Ihr) or Ldn from the Leq(Ihr) or Ldn of a comparable site where the ambient noise is dominated by the same source that is comparable in precision to Option 4. This method can be used to characterize noise in several neighborhoods by using a single representative receiver. It is critical that the measurement site has a similar noise environment to all areas represented. If measurements made by others are available and the sites are equivalent, the existing measurements can be used to reduce the amount of project noise monitoring. The following procedures apply to this method of determining of ambient noise:
■ Choose another receiver that is comparable to the receiver (CompRec) of interest with the following:
The same source of dominant ambient noise
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• The ambient level of the comparable receiver was measured according to Option I or Option 2 above
• The ambient measurement at the comparable receiver was made in direct view of the major source of ambient noise, unshielded by noise barriers, terrain, rows of buildings, or dense tree zones
• Determine the following from a plan or aerial photograph:
• The distance (DCompRec) from the comparable receiver to the near edge of the ambient source
• The distance (DRec) from this receiver of interest to the near edge of the ambient source • Determine the number of rows of buildings (N) that intervene between the receiver of interest and the ambient source.
• Compute the ambient level at the receiver of interest (Rec) with the appropriate equation below
If roadway sources dominate:
DRec
LRec LCompRec — 151og( ) 3N
DCompRec
If other sources dominate:
DRec
LRec LcompRec — 251og( ) 3N
DCompRec
Eq. E-5
Eq. E-6
The resulting LRec will be moderately underestimated. This underestimation is intended to compensate for the reduced precision of the computed Ldn.
Option 6: Estimation of Ldn by table look -up (all land uses) — The least precise way to determine the ambient noise is to estimate the level using a table. A tabular look -up can be used to establish baseline conditions for a General Noise Assessment if a noise measurement cannot be made. This method should not be used for a Detailed Noise Analysis. The following instruction applies to this method of determining of ambient noise:
Estimate either the Leq(Ihr) or the Ldn using Table 4-17 based on distance from major roadways, rail lines, or upon population densities. In general, these tabulated values are substantially underestimated.
The underestimation is intended to compensate for the reduced precision of the estimated ambients.
Examples — Examples of when each method of determining existing noise may be appropriate are provided below using the example from Appendix D. Existing noise at the receivers labeled "REC" in Figure D- I could be estimated as follows:
• Option I: Leq(Ihr) measurement — Existing noise at REC I is due to the highway at the side of this church. Leq(Ihr) can be measured during a typical church hour. • Option 2: Ldn measurement — Existing noise at the residence REC 2 is due to a combination of the highway and local streets. Ldn can be measured for a full 24 -hours. • Option 3: Ldn computation of Ldn from 3 partial Leq(inr> measurements — Existing noise at the residence REC 3 is due to the street in front of this residence. Ldn can be computed from three Leq(Ihr) measurements.
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■ Option 4: Computation of Ldn from I partial Leq(Inr) measurement — Existing noise at the residence REC 4 is due to the highway. Because the highway has a predictable diurnal pattern, Ldn can be computed from one Leq(inr> measurement. ■ Option 5: Computation of Ldn from Ldn of a comparable site — Existing noise at the residence REC 5 is due to Kee Street. REC 3 is also affected by local street traffic and is a comparable distance from the highway. Ldn for REC 5 can be computed based on the Ldn at REC-3.
■ Option 6: Estimation of Ldn by table look -up — Existing noise at the residence REC 6 is due to local traffic. Ldn can be estimated by tables based on population density along this corridor. 4994
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Appendix F: Computing Source Levels from
Measurements
This appendix contains the procedures for computing source reference levels (SELref) from source measurements in cases where the source reference tables in Section 4.5, Step 2 indicate measurements are preferred, data are not available for the source of interest, or more precise data are required than available in the table.
Close -by source measurements for vehicle passbys may capture either the vehicle's sound exposure level (SEL) or maximum noise level (Lmax). Both metrics can be measured directly by commonly available sound level meters. While the Lmax metric is not used for transit noise impact assessments, it can be used to compute SEL source reference levels. Lmax measurements are often available from transit - equipment manufacturers and some transit system equipment specifications may limit close -by Lmax levels.
Close -by source measurements for stationary sources capture the source's SEL over one source event, where the event duration may be chosen based on measurement convenience. The duration will factor out of the computation when the measured value is converted to reference operating conditions.
This manual does not specify elaborate methods for undertaking the close -by source measurements, but rather, provides general processes. It is required that all measurements conform to good engineering practice, guided by the standards of the American National Standards Institute and other such organizations (27, 28, 29).
This appendix presents information according to noise source as follows:
• Appendix F. I : Highway and rail vehicle passbys for vehicles of the same type • Appendix F.2: Stationary sources
• Appendix F.3: Lmax for single train passbys (for trains of mixed consists) F. I Highway and Rail Vehicle Passbys
This section provides information on appropriate conditions for vehicle passby measurements, instructions on converting measurements made under non -reference conditions to source reference levels, and examples of these computations.
The following conditions are required for vehicle passbys, in addition to good engineering practice:
• Measured vehicles must be representative of project vehicles in all aspects, including representative acceleration and speed conditions for buses. • Track must be relatively free of corrugations and train wheels relatively free of flats, unless these conditions are typical of the proposed project.
I. Road surfaces must be smooth and dry, unless these conditions are typical of the proposed project.
I. Perpendicular distance between the measurement position and the source's centerline must be 100 ft or less.
• Vehicle speed must be 30 mph or greater, unless typical project speeds are less than that. • No noise barriers, terrain, buildings, or dense tree zones may break the lines -of -sight between the source and the measurement position.
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When close -by source measurements are made under non -reference conditions, use the instructions below and the equations in Table F- I to convert the measured values to source reference levels. For rail vehicles, measure/convert a group of locomotives or a group of cars separately. This computation requires that all measured vehicles be of the same type. For trains of mixed consists, see Appendix F.3.
SEL measured for a highway -vehicle passby, or a passby of a group of identical rail vehicles • Collect the following input information:
o SELmeas, the measured SEL for the vehicle passby
o N, the consist of the measured group of rail cars or group of locomotives o T, the average throttle setting of the measured diesel -powered locomotive(s) • Smeas, the measured passby speed, in miles per hour
o Dmeas, the closest distance between the measurement position and the source, in feet • Compute the Source Reference Level SELref, using Eq. F -I.
L. measured for a passby of a group of identical rail vehicles ■ Collect the following input information:
o Lmax, measured for the group passby
o N, the consist of the measured group of rail cars or group of locomotives o T, the average throttle setting of the measured diesel -powered locomotive(s) o Smeas, the measured passby speed, in miles per hour
▪ Dmeas, the closest distance between the measurement position and the source, in feet o Lmeas, the total length of the measured group of locomotives or group of rail cars, in feet ■ Compute the Source Reference Level SELref, using either Eq. F-2 or Eq. F-3, as appropriate, for locomotives or rail cars.
Lmax measured for a highway -vehicle passby
• Collect the following input information:
• Lmax, measured for the highway -vehicle passby
o Smeas, the vehicle speed, in miles per hour
o Dmeas, the closest distance between the measurement position and the source, in feet ■ Compute the Source Reference Level, SELref, using Eq. F-4. 4996
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Table F -I Conversion to Source Reference Levels at 50 ft - Highway and Rail Sources Measured
Source
Equation
SEL
Vehicle
passby
Smeas Smeas
SELref SELmeas 101og( 101og( Cconsist Cemissions
Eq. F -I
= + +
50 ) +
50 ) +
Lora.
Rail -vehicle
passby,
locomotives
only
SELref LAmax 101og(L s) 101og(D50s) 10log(2 Cconsist
Eq. F-2
= + + 00+
50 +Cemissions + 3.3
Rail -vehicle
passby,
cars only
SELref LAmax 101og(L s) 101og(DS0as) 10log
Eq. F-3
= + + [2 cc + sin(2 a)]
50 +Cconsist + Cemissions + 3.3
Highway -
vehicle
passby
D,
SELref = LAmax + 201og( 0as) + C + 3.3
Cemissions
Eq. F-4
Smeas =
Dmeas =
Cconsist =
Cemission =
s
Emeas =
Leas =
a =
speed of measured vehicle(s), mph
closest distance between measurement position and source, ft 0 for buses and automobiles
—101og(Ncars) for locomotives and rail cars
where N is the number of locomotives or rail cars in the measured group O for T < 6 for locomotives
-2 (T-5) for T ≥ 6
where T is average throttle setting of measured diesel — electric locomotives) mea
s) for
rail cars
—30log(S50
s) for buses
—25log(S50
for automobiles
—38.11og(Smeas50)
event duration
total length of
Lmeas
of measurement, sec
measured group of locomotives or rail cars, ft
), rad
arctan(
2Dmeas
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Example F -I Calculate SELref — Locomotives
Computation of SELreffrom SEL Measurement of Fixed -guideway Source SEL was measured for a passby of two diesel -powered locomotives with the following conditions:
SELmeas = 90 dBA
NCars = 2
T =6
Smeas = 55 mph
DmPa = 65 ft
Compute the source reference level using Eq. F -I.
SELref = SELmeas + 101og(\S50 s) + 1010g\(D50as) + Cconsist + Cemissions = 90 + 101og (50 I + 101og 150 I - 101og(2) + (-2(6 — 5)) = 86.5 dBA / \ /
Example F-2 Calculate SELref — Rail Cars
Computation of SELref from Lmax Measurement of Fixed -Guideway Source Lmax was measured for a passby of a 4 -car consist of 70 -ft long rail cars with the following conditions:
Lmax = 90 dBA
Ncars = 4
Smeas = 70 mph
Dmeas = 65 ft
Lmeas = 280 ft
a = 1.14
Compute the source reference level using Eq. F-3.
SELref = LAmax + l0log(L 50 s) + 101og( 50 s) 10 log [2 a + sin(2 a)] + Cconsist + Cemissions + 3.3 65 70
= 90 + lO log( 50 ) + 10log(SO) — lO log [2(1.14) + sin(2(1.14))] — lO log(4) — 301og(5O) + 3.3 = 86.7 dBA
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Example F-3 Calculate SELref — Bus
Computation of SELref from Lm Measurement of Highway Vehicle Source Lmax was measured for a bus with the following conditions:
Lmax = 78 dBA
Dmeas = 80 ft
Smeas = 40 mph
Compute the source reference level using Eq. F-4
= Lmax + 201og( 50as) + Cemissions + 3.3
80 40
= 78 + 201og(50) — 251og(50) + 3.3
= 87.8 dBA
F.2 Stationary Sources
This section provides information on appropriate conditions for stationary source measurements, instructions on converting measurements made under non -reference conditions to source reference levels, and an example of this type of computation.
The following conditions are required for stationary sources, in addition to good engineering practice:
• Measured source operations must be representative of project operations in all aspects. • The following ratio must be 2 or less, and the distance to the closest source component must be 200 ft or less.
Distance to the farthest source component
Distance to the closest source component
If both conditions cannot simultaneously be met, separate close -by measurements of individual components of this source must be made, for which these distance conditions can be met. ■ The following ratio must be 2 or less:
Lateral length of the source area
Distance to the closest source component
The lateral length of the source area is measured perpendicular to the general line -of -sight between source and measurement positions.
If this condition cannot be met, then make separate close -by measurements of individual components of this source, for which this condition can be met. • No noise barriers, terrain, buildings, or dense tree zones may break the lines -of -sight between the source and the measurement position.
When close -by source measurements are made under non -reference conditions, use the instructions below and the equation in Table F- 2 to convert the measured values to source reference levels. 4999
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SEL was measured for a stationary noise source
■ Collect the following input information:
o SELmeas, the measured SEL for the noise source, for whatever source "event" is convenient to measure
o Emeas, the event duration, in seconds
o Dmeas, the closest distance between the measurement position and the source, in feet • Compute the source reference level, SELref using Eq. F- 5.
Table F-2 Conversion to Source Reference Levels at 50 ft - Stationary Sources Measured
Source
Equation
SEL
Stationary
noise source
Emeas Dmeas Eq. F- 5
SELref SELmeas 201og(
101og(3600)
= — +
50 )
Smeas = speed of measured vehicle(s), in miles per hour Emeas = event duration of measurement, in seconds
Dmeas = closest distance between measurement position and source, in feet Example F-4 Calculate SELref — Signal Crossing
Computation of SELref from SEL Measurement of Stationary Source SEL was measured for a signal crossing with the following conditions:
SELmeas = 70 dBA
Emeas = I O sec
Dmeas = 65 ft
Compute the source reference level using Eq. F-5.
SELref = SELmeas — 10log(Emeas Dmeas
3600) + 201og( 50 )
10 65
= 70 - 10log(3600) + 201og(50)
= 97.8 dBA
F.3 Lmax for Single Train Passby
This section provides procedures for the computation of Lmax for a single train passby. This procedure can be used to characterize trains of mixed consists using Lmax. Follow the instructions below. • Collect the following input information:
o SELref, from Section 4.5, specific to both the locomotive type and car type of the train o N,oco, the number of locomotives in the train
o Ncars, the number of cars in the train
o LLoco, the total length of the train's locomotive(s), in feet (or Moto unit length) o Lcars, the total length of the train's set of rail car(s), in feet (or Ncars unit length) • S, the train speed, in miles per hour
▪ D, the closest distance between the receiver of interest and the train, in feet • Use the equations in Table F-3 to compute the following:
o Lmax.iocofor the locomotive(s) using Eq. F-6
FEDERAL TRANSIT ADMINISTRATION 234
5000
° Lmax.cars for the rail car(s) using the Eq. F-7
° Lmax total, the larger Lmax from the locomotives(s) and rail car(s) is the Lmax for the total train passby, see Eq. F- 8.
Table F-3 Conversion to Lmax at the Receiver, for a Single Train Passby Source
Equation
Locomotives
Lmax.Loco locos .g (—)-10log = SEL + 1010 S (-50) g(+ lOlo (2 a) 50 3.3 Eq.
F-6
Rail Cars
Lmax.Rcars = SELRcars + 101og (-50) — 10log (—)+0 101og(2 a + sin(2 cc)) — 3.3
Eq. F-7
Total Train
/
Lmax.totai = maxlLmax.Goco or Lmax.RCarS )
Eq. F-8
L = total length of measured group of locomotive(s) or rail car(s), ft S = vehicle speed, mph
a = arctan (M, rad
D = closest distance between receiver and source, ft
5001
FEDERAL TRANSIT ADMINISTRATION 235
Example F-5 Calculate Lmax — Train Passby
Computation of Lmax for Train Passby
Calculate the Lmax of commuter train at receiver of interest according to the following conditions:
SELref = 92 dBA for locomotives
= 82 dBA for rail cars
NLoco
Ncars = 6
S = 43 miles per hour
D = 125 ft
«locos = 0.27
«cars = 1.03
The locomotive and rail cars each have a unit length (L) of 70 ft.
Determine the total length of the locomotive and rail cars.
Loco = 70 ft
Lars = 420 ft
Compute Lmax for the locomotive using Eq. F-6:
Lmax.Loco
S L
= SELloco + 1/0log\ 50 )-10log (50)
(50) + 101og(2 a) — 3.3
=92+10log1501-10log +101og(2x0.27)-3.3
= 84.0 dBA \\\ /ll
Compute Lmax for the rail cars using Eq. F-7:
Lmax.Rcars
= SELRcars + 10log (50) - 10log (5L0 I + 101og(2 a + sin(2 a)) — 3.3 = 82 + 10log (43)5 — 10log (50) + 101og((2 x 1.03) + sin(2 x 1.03)) — 3.3 = 73.5 dBA
Find the total Lmax for the train passby using Eq. F-8.
Lmax.total = max(Lmax.Loco or Lmax.Rcars )
=84.0 dBA
5002
FEDERAL TRANSIT ADMINISTRATION 236
Appendix G: Non -Standard Modeling Procedures and
Methodology
This manual provides guidance for preparing and reviewing the noise and vibration sections of environmental documents, as well as FTA-approved methods and procedures to determine the level of noise and vibration impact resulting from most federally -funded transit projects. Situations may arise, however, that are not explicitly covered in this manual. Professional judgment may be used to extend the basic methods to cover these cases, when appropriate. It is important to note that each project is unique and must be evaluated on a case -by -case basis. This appendix provides procedures for the use of non-standard noise and vibration modeling procedures and methodologies on public transportation projects.
Submittal Procedure — The procedure for using non-standard modeling procedures and methodology is as follows:
I. The transit project manager should contact the FTA Regional office to discuss the proposed methods and/or data not described in this manual prior to use of the non-standard approach.
2. The non-standard methodology should be documented according to the guidelines below as part of the technical report described in Section 8.2.
Examples of Methods that Require Communication and Documentation — The following noise and vibration analysis methods and data require communication with the FTA Regional office and documentation:
■ Non-standard transit noise and vibration modeling and analysis methods not described in this manual (including non-standard adjustments, computations, and assumptions). This includes modifications to standard FTA noise and vibration methods. ■ Non-standard transit noise and vibration reference data not described in this manual (including measured data, substitution data, data at non-standard reference distances and/or speeds, new transit noise sources, and transit noise sources operating in non-standard conditions). ■ Non-standard transit noise and vibration impact criteria not described in this manual, including the maximum sound pressure level metric.
■ Non-standard methods of evaluating construction noise, including non-standard construction noise impact criteria.
■ Other noise modeling tools besides the FTA Noise Impact Assessment Spreadsheet or Traffic Noise Model (TNM®) for highway noise modeling, such as the development of a finite element method model.
■ Any transit noise and vibration analysis that involves an impact area or noise source that is controversial.
Documentation Guidelines — The use of non-standard noise and vibration analysis methods or data requires the following documentation components in a technical memorandum attached to the environmental document:
■ Background
Briefly describe the transit project for which non -default methods or data are needed. State the dominant noise sources, type of analysis, and the impact criteria. Include any additional relevant information.
FEDERAL TRANSIT ADMINISTRATION 237
5003
• Statement of Benefit
Briefly describe the benefit of the non -default noise and vibration methods or data to the transit project. Describe the appropriateness of the non -default methods or data, as well as why the standard method or data are insufficient or problematic. • Non-standard Data Description
Describe the non-standard noise or vibration data in detail. Include source type, manufacturer, reference conditions (speed, distance, and operational conditions), name of data supplier, and a date associated with data development/measurement. For measured noise or vibration data, provide corresponding data documentation (such as a data measurement or a development report). For substitution data, a comparison between the non-standard data and corresponding standard data should be provided. Furthermore, if outside sources recommend the use of the non-standard data (such as a technical society, a standards organization, or a vehicle manufacturer), references for those recommendations should be included. • Non-standard Methods Description
Describe the non-standard noise or vibration analysis method in detail. This should include a detailed description and derivation of the method (including data used in the development of the method), a description of the usage of the method, and a comparison between the non-standard method and the corresponding standard method in the context of the transit analysis. If the method has been validated against measurement data, a description of that validation analysis should be provided. If the method is derived from another source (such as a different transportation noise or vibration method), provide corresponding documentation for that source. A description of how the method is conservative (for example, estimating the worst - case scenario) or some discussion on the probability of exceeding the predicted level should be provided. Furthermore, if outside sources recommend the use of the non-standard method (such as a technical society or standards organization), references for those recommendations should be included.
• Non-standard Tools Description
Describe in detail any non-standard noise or vibration models that have not been explicitly recommended in this manual. This should include a detailed description of the tool (including data used, the computations implemented in the tool, any modifications or adjustments to the tool or the corresponding data, and the usage of the tool), a description of the validation of the tool (including reference documentation and validation analyses), and a comparison between the non-standard tool and the equivalent standard tool in the context of the transit analysis.
Quantitative comparisons, such as the standard deviation of the non-standard tool and an estimate of the least mean square of differences between the standard and non-standard tools, should be provided and explained. A description of how the method is conservative (for example, estimating the worst -case scenario) or some discussion on the probability of exceeding the predicted level should be provided. If outside sources recommend the use of the non- standard tool (such as a technical society or standards organization), references for those recommendations should be included.
5004
FEDERAL TRANSIT ADMINISTRATION 238
ENDNOTES
Regulations for Implementing the Procedural Provisions of the National Environmental Policy Act, Council on Environmental Quality, 40 CFR parts 1500-1508, 1978.
2 3
4 s
6 7
8 9
Io
I2
13 14
National Environmental Policy Act of 1969, United States Congress, 42 U.S.C §433 I, 1969.
U.S. Department of Transportation, Federal Transit Administration and Federal Highway Administration, "Environmental Impact and Related Procedures," Final Rule, 52 Federal Register 32646-32669, January 2014 (23 CFR part 771).
U.S. Department of Transportation, Federal Transit Administration and Federal Highway Administration, "Planning Assistance and Standards." Final Rule, 58 Federal Register 58064, June 2014 (23 CFR part 450).
U.S. Environmental Protection Agency, "Information on Levels of Environmental Noise Requisite to Protect Public Health and Welfare with an Adequate Margin of Safety," Report No. 550/9-74-004, Washington DC, March 1974.
Federal Interagency Committee on Urban Noise, "Guidelines for Considering Noise in Land Use Planning and Control," Environmental Protection Agency, the Department of Transportation, the Department of Housing and Urban Development, the Department of Defense, and the Veterans Administration, Washington DC, June 1980.
U.S. Department of Housing and Urban Development, "Environmental Criteria and Standards of the Department of Housing and Urban Development," Final Rule, 44 Federal Register 40861, Washington DC, 12 July 1979 (24 CFR part 51).
American National Standards Institute, "Compatible Land Use With Respect to Noise," Standard S3.23-1980, New York NY, May 1980.
American National Standards Institute, "Quantities and Procedures for Description and Measurement of Environmental Sound," ANSI SI2.9-1998/Part 5, New York. NY, January 1998.
T. J. Schultz, "Noise Rating Criteria for Elevated Rapid Transit Structures," U.S. Department of Transportation, Report No. UMTA-MA-06-0099-79-3, Washington DC, May 1979.
T. J. Schultz, "Synthesis of Social Surveys on Noise Annoyance," Journal of the Acoustical Society of America, Vol. 63, No. 8, August 1978.
S. Fidell, D.S. Barber, T.J. Schultz, "Updating a Dosage -Effect Relationship for the Prevalence of Annoyance Due to General Transportation Noise," Journal of the Acoustical Society of America, Vol. 89, No. I, January 1991.
S. Fidel, "The Schultz Curve 25 -years Later: A Research Perspective," Journal of the Acoustical Society of America, Vol. 1 14, No. 6, Pt. I, December 2003.
"High -Speed Ground Transportation Noise and Vibration Impact Assessment", DOT/FRA/ORD-12/15, U.S.
Department of Transportation Federal Railroad Administration, 2012. 15 National Historic Preservation Act, Section 106; P.L. 89-665, 15 October 1966. 16 The Department of Transportation Act of 1966, Section 4(f); P.L. 89-670, 15 October 1966. 17 U.S. Department of Transportation, Federal Transit Administration and Federal Highway Administration, "Protection of Historic Properties." Final Rule, 65 Federal Register 77725, July 2013 (36 CFR 800). 5005
FEDERAL TRANSIT ADMINISTRATION 239
18 19
20 21
22 23
24 25
26 27
28 29
30 31
32 33
34 "Eligibility and Justification Requirements for Noise Insulation Projects," Program Guidance Letter 12-09, November 2012. https://www.faa.gov/airports/aip/guidance letters/historicalguidance letters/media/aip-pgl- 20 12-09-noise-insulation.pdf.
U.S. Department of Housing and Urban Development, "Environmental Criteria and Standards", Vol. 12, July 979; amended by 49 Federal Register 880, 6 January 1984 (24CFR part 51).
U.S. Department of Transportation, Federal Aviation Administration, "Federal Aviation Regulations Part 150:
Airport Noise Compatibility Planning," January 1981.
U.S. Department of Transportation, Federal Railroad Administration, "Use of Locomotive Horns at Public Highway -Rail Grade Crossings." Final Rule, 70 Federal Register 21844, October 2013 (49 CFR 222).
U.S. Department of Transportation, Federal Highway Administration, "FHWA Traffic Noise Model User's Guide," Report No. FHWA-PD-96-009, Washington, DC, January 1998. Also, "FHWA Traffic Noise Model User's Guide (Version 2.5 Addendum)," April 2004.
J.C. Ross, C.E. Hanson, R.V. Hartz, "Houston Southeast Corridor Environmental Impact Statement BRT Noise and Vibration Assessment," technical memorandum prepared by Harris Miller Miller & Hanson for Metropolitan Transit Authority of Harris County Houston, Texas, September 20, 2005.
U.S. Environmental Protection Agency, "Population Distribution of the United States as a Function of Outdoor Noise Level," Report No. 550/9-74-009, June 1974.
T. M. Johnson, "The Importance of Vehicle Throttle Setting Information for Rail Transit Noise Impact Assessments," Proc. Inter -Noise 2012, New York, NY, August 2012.
U.S. Department of Transportation, Federal Highway Administration, "FHWA Highway Traffic Noise Prediction Model," FHWA-RD-77-108, December 1978.
American National Standards Institute, "American National Standard Quantities and Procedures for Description and Measurement of Environmental Sound, Part 4: Noise Assessment and Prediction of Long-term Community Response," ANSI 12.9-1996, New York, 1996.
C. Harris, "Handbook of Acoustical Measurements and Noise Control." International Organization for Standardization "Acoustics -- Attenuation of sound during propagation outdoors -- Part 2: General method of calculation." ISO 9613-2.
American Society for Testing and Materials, "Standard Guide for Measurement of Outdoor A -weighted Sound Levels," E 1014-84, Philadelphia, 1984.
American National Standards Institute, "Method for the Measurement of Sound Pressure Levels," ANSI S I . 13-1971(R 1976), New York, 1971.
U.S. Department of Transportation, Federal Highway Administration, "Measurement of Highway -Related Noise," FHWA-PD-96-046, May 1996.
J.T. Nelson, "Wheel/Rail Noise Control Manual," Transportation Cooperative Research Report No. 23, Transportation Research Board, Washington, DC, 1997.
"Challenges in Maintaining Quiet Streetcar and Light Rail Systems," Session No. 409, Transportation Research Board Annual Meeting, Washington DC, January 2014.
5006
FEDERAL TRANSIT ADMINISTRATION 240
35 36
37 38
39 40
41 42
43 44
45 46
47 48
49 50
U.S. Department of Transportation, Federal Railroad Administration, "Use of Locomotive Horns at Highway - Rail Grade Crossing," Final Rule, 70 Federal Register 21844, April 27, 2005 (49 CFR 222). "Interim Final Rule for the Use of Locomotive Horns at Highway -Rail Grade Crossings," Federal Railroad Administration, Final Environmental Impact Statement, December 2003.
T.A. Busch, R.E. Nugent, "A Reduced -Scale Railway Noise Barrier's Insertion Loss and Absorption Coefficients: Comparison of Field Measurements and Predictions," Journal of Sound and Vibration, 749-759, October 2003.
U.S. Department of Transportation, Federal Highway Administration, "Highway Noise Barrier Design Package," August 2000.
"High -Speed Ground Transportation Noise and Vibration Impact Assessment," DOT/FRA/ORD-12/15, U.S.
Department of Transportation Federal Railroad Administration, 2012.
American National Standards Institute, "Guide to Evaluation of Human Exposure to Vibration in Buildings," ANSI S3.29 -I983 (ASA 48-1983).
International Organization for Standardization, "Evaluation of Human Exposure to Whole -Body Vibration, Part 2: Continuous and Shock -Induced Vibrations in Buildings (I-80Hz)," ISO -2631-2, 1989.
International Organization for Standardization, "Mechanical Vibration and Shock: Evaluation of Human Exposure to Whole Body Vibration: Part 2 — Vibration in Buildings (I to 80 Hz)," ISO -2631-2, 2003.
J. T. Nelson, H. J. Saurenman, "State -of -the -Art Review: Prediction and Control of Ground -borne Noise and Vibration from Rail Transit Trains," U.S. Department of Transportation, Urban Mass Transportation Administration, Report No. UMTA-MA-06-0049-83-4, DOT-TSC-UMTA-83-3, December 1983.
Y. Tokita, "Vibration Pollution Problems in Japan," Inter -Noise 75, Sendai, Japan, 1975. (pp. 465-472) J. A. Zapfe, H. Saurenman, S. Fidell, "Ground -Borne Noise and Vibration in Buildings Caused by Rail Transit," Transportation Research Board, Final Report for TCRP Project D- 12, December 2009.
J.T. Nelson, H.J. Saurenman, G.P. Wilson, "Handbook of Urban Rail Noise and Vibration Control," prepared under contract to U.S./DOT Transportation Systems Center, Report No. UMTA-MA-06-0099-82-2, February 1982.
International Organization for Standardization, "Mechanical Vibration — Ground -borne Noise and Vibration Arising from Rail Systems," ISO/FDIS 14837-1:2005.
Institute of Environmental Sciences and Technology, "Considerations in Clean Room Design," RR-CC0I2. 3, 2015.
U.S. Department of Transportation, Volpe National Transportation Systems Center, "Vibration Characteristics of the Transrapid TR08 Maglev System," Report No. DOT-VNTSC-FRA-02-06, March 2002.
S. McKenna, "A Study of Build Amplification from Ground -Borne Vibration," Noise -Con 2011, Portland, Oregon, July 25-27, 201 I.
51 American National Standards Institute, "Acoustical Terminology," ANSI S I . I - 1994. 52 J.T. Nelson, H.J. Saurenman, "A Prediction Procedure for Rail Transportation Ground -Borne Noise and Vibration," Transportation Research Record, 1143, August 1988. 5007
FEDERAL TRANSIT ADMINISTRATION 241
53 54
55 56
57 58
59 60
61 62
63 64
65 66
67 68
69 J. T. Nelson, "Tri-Met Track Vibration Isolation Tests," Final Report for Portland Tri-Met, October 1998.
J.T. Nelson, H.J. Saurenman, "Ground -Borne Vibration Tests with MARTA C -Car," report prepared for Metropolitan Atlanta Rapid Transit Authority, November 16, 1981.
H.J. Saurenman, "Preliminary Results of Ground -Borne Vibration Tests with BRRT/Miami Vehicle," technical memorandum prepared for US DOT/Transportation Systems Center, contract DOT-TSC-1796, 8 February1983.
H.J. Saurenman, "Ground -borne Vibration Tests with NFTA Prototype Vehicle at the Transportation Test Center," technical memorandum prepared for Transportation Test Center, Project No. P -83-C-01078, 3 August 1983.
H.J. Saurenman, "Noise and Vibration Tests with Portland Tri-Met Prototype Vehicle at the Transportation Test Center," technical memorandum prepared for Transportation Test Center, Project No. P -83-C-02649, 26 March 1984.
R.A. Carman, D.L. Watry, "Measured Vibration Reduction Performance of Ballast Mat Installation for Light Rail Vehicles on Embedded Track," APTA, 1997 Rapid Transit Conference of the APTA, V. 3 -Way & Structures and Construction (1997-8).
D.A. Towers, "Evaluation of the Ground -Borne Vibration Reduction Properties of Tire Derived Aggregate Installed on the Denver RTD Light Rail System," Harris Miller Miller and Hanson Inc., 2012.
F. E. Richert, J. R. Hall, Vibrations of Soils and Foundations, Prentice -Hall, Inc., Englewood Cliffs, NJ, 1970.
U.S. Environmental Protection Agency, "Noise from Construction Equipment and Operations, Building Equipment and Home Appliances," NTID300.I, 31 December 1971.
Society of Automotive Engineers, "Exterior Sound Level Measurement Procedure for Powered Mobile Construction Equipment," SAE Recommended Practice J88a, 1976.
Society of Automotive Engineers, "Sound Levels for Engine Powered Equipment," SAE Standard J952b, 1976.
U.S. Department of Transportation, Federal Highway Administration, "FHWA Roadway Construction Noise Model User's Guide," FHWA-HEP-05-054, January 2006. Available at http://www.fhwa.dot.gov/environment/noise/construction noise/rcnm/.
E. Thalheimer, "Construction noise control program and mitigation strategy at the Central Artery/Tunnel Project," Noise Control Eng. J. 48(5), September —October 2000, 157-165).
U.S. Department of Transportation, Federal Highway Administration. "Highway Construction Noise Handbook," FHWA-HEP-06-0I5, August 2006.
D.J. Martin, "Ground Vibrations from Impact Pile Driving during Road Construction," Supplementary Report 544, United Kingdom Department of the Environment, Department of Transport, Transport and Road Research Laboratory, 1980.
J.F. Wiss, "Vibrations during Construction Operations,"Journal of Construction Division, Proc.
American Society of Civil Engineers, 100, No. CO3, 239-246, September 1974.
J.F. Wiss, "Damage Effects of Pile Driving Vibrations," Highway Research Record, No. 155, Highway Research Board, 1967.
5008
FEDERAL TRANSIT ADMINISTRATION 242
70 71
72 73
74 75
76 77
D.A. Towers, "Ground -borne Vibration from Slurry Wall Trench Excavation for the Central Artery/Tunnel Project Using Hydromill Technology," Proc. InterNoise 95, Newport Beach, CA, July 1995.
Swiss Consultants for Road Construction Association, "Effects of Vibration on Construction," VSS-SN640-3 I 2a, Zurich, Switzerland, April 1992.
American Public Transportation Association, Public Transportation Factbook, 55th Edition, March 2004.
American National Standards Institute, "Preferred Frequencies, Frequency Levels and Band Numbers for Acoustical Measurements," ANSI S1.6-1984 (R2006).
U.S. Environmental Protection Agency, "Information on Levels of Environmental Noise Requisite to Protect Public Health and Welfare with an Adequate Margin of Safety," EPA Report No. 550/9-74-004, March 1974.
National Academy of Sciences, "Guidelines for Preparing Environmental Impact Statements on Noise," Report from Committee on Bioacoustics and Biomechanics (CHABA) Working Group 69, February 1977.
American Public Transit Association, "Noise and Vibration," 1981 Guidelines for Design of Rapid Transit Facilities, Section 2.7, 1981.
T.J. Schultz, "Synthesis of Social Surveys on Noise Annoyance,"Journal of the Acoustical Society of America, Vol. 64, No. 2, August 1978, 377-405.
5009
FEDERAL TRANSIT ADMINISTRATION 243
a
U.S. Department of Transportation
Federal Transit Administration
U.S. Department of Transportation
Federal Transit Administration
East Building
1200 New Jersey Avenue, SE
Washington, DC 20590
https://www.transit.dot.gov/about/research-innovation
5010
EXHIBIT E
5011
Conservancy Territory Map
ippe Miss ton CreeklSlg Maarrgo Canyon
Wear Deception
Canyon
do
1 \.
j 1
RANCHO MIRAGE '. '�
PALM,DESER
--' • -. . . :- INDIAN WELLS,.
Thousand Palms
CONSER%A7lON AREAS Eden) HN Cosereaton Area
jI Cabes.on Conservation Area IM Highway 11WG1O Conservation Area Coachella Vevey Stemmata.' Channel and Gana Canserwahan Area - leak, Hills pain , Canserakon Ar a� m
t'� Desert -Tortoise end Linkage Cmservahan Area - Indio HiltstJoshua Tr. National Park Llama Coseervevon Area Q Snow Crane/Windy Pent Conmreation Ham Dee Palmas Cmservalson Area Joshua Ties National Park Conservation teas FT Stubbs and Celtennwood Canyons Con ervaHen Aaaa El East Indio Ties Conservation Area IM Long Canyon Conesrvehsr Area IM Thousand Palms Conearration Ara
CCACHELLA
Indio Hilts Paints
Salton Sea
® Macre Hilo 'Onssepa Mountains CSauervatiau Area
- Morongo Wash Spada' Provisions Area -.
Santa Rosa end San Japnlu Mountain, Cori servals. AMAMI Desert Tortoise and tankage Con -seem bon Area
Mac. Hills l Orxa pro Mountains Conservahio n Aren
Upper Mission C onselliyMaronlp Canyon Conservation Area West Oacepeon Canyon Conservation Area
Wastewater Canyon Congarontinn Area
VASSawater €laee}atain Conaervatien Area
aicMfieow Hots Conservation Area
Wells'k311ey MSHCP ,area.
20 Miles
5012
EXHIBIT F
5013
1 -REBECCA WY
2 - EMILY WY
3- ANITA WY
4- CARA WY
5- DENISE WY
6 -HEATHER WY
- LAURA WY
6• KAREN WY
VICTORIA DR
NELLIE N.
COFFMAN
MIDDLE
SCHOOL
A - LOCH NESS LAKE
S - CEDAR LAKE CT
C - LAKE COMO CT
D - PYRAMID LAKE CT
E - LAKE GENEVA CT
F - LAKE LOUISE CT
G - CALIFORNIA LAKES DR
FI - LAKE TAHOE DR
J - LAKE MENDOCINO OR
K • CANYON LAKE DR
L- CLEAR LAKE DR
M - MOON LAKE DR
36TH AV
CATHEDRAL CITY
ELEMENTARY
SCHOOL
CJ
NIG7yl 40„ 777
M
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ire
CONVERSE RD
GERALD FORD DR
34 1 - CALLE REGINA
2-CALLE LSTA
3-CALLE SOLANO
1- CALLE MERIDA
5- CALLE RIVER°
6 - CALLE NAVARROS
7 - CALLE VEGA
0- CALLE ESCALA
9 - CALLE ARDILLA
10 -AVEINDA DEL SOL
I • VIA DEL PARADISO
2 - VIA DEL PIENZA
3- VIA DEL MARICALE
4 - VIA DEL MERCATO
5 -VIA MONTECASSINO
DINAH SHORE DR
RAMON RD
o
Land Use and Zoning Map
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CITY OF RA NC
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ROW
RESIDENTIAL
Residential Estate 1 du/ac Max.
Very Low Density 2 du/ac Max.
Low Density 3 du/ac Max.
Medium Density 4 du/ac Max.
High Density 9 du/ac Max
Mobile Home Park 9 du/ac Max.
Hillside Reserve 1 du/640 ac Max
COMMERCIAL
Office 112
Neighborhood Commercial 103
General Commercial 233
Community Commercial 342
Resort Hotel 387
Mixed Use (Commercial/Office/Residential) 71
Regional I nterstate Commercial 186
ACREAGE
City Sphere Total
511 511
2,102 2,102
961 961
1,154 801 1,955
206 39 245
95 95
345 345
Sub -Total 5,374
INSTITUTIONAL
Public/Quasi-Public
City Hall
Fire Station
Hospital
School
Library
Post Office
Utility Station
OPEN SPACE
Public Park
Mountain Reserve
Private Open Space
Floodways and Drainage Channels
840 6,214
112
103
233
75 417
387
71 186
Sub -Total 1,435
83 9
4 132
83 10
3 9
75 1,510
83 9
4 132
39 121
10 3
9 Sub -Total 332 39 371
Right of Way
Totals
OVERLAYS*
Senior Overlay
Special Corner
111 West Specific Plan
111 East Specific Plan
Agua Caliente Band of Cahuilla Indians
Sub -Total
55 41 96
5,175 5,175
2,129 181 2,311
332 332
7,691
1,239
222 7,913
27 1,265
16,070
25 8 ac
122 ac
121 ac
248 ac
2,027 ac
* These acreages are included in land use acreages above.
Entry Gates to Private Communities
Note: Figures are subject to rounding.
CATHEDRAL CITY
HIGH SCHOOL
l
1,202 17,272
2 27 Sq. Miles
ll
_ I ➢.. L�
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P: (626) 381-9248
F: (626) 389-5414
E: [email protected]
Mitchell M. Tsai
Attorney At Law
139 South Hudson Avenue
Suite 200
Pasadena, California 91101
VIA EMAIL
March 24, 2023
Ben Torres
Planning Manager
69-825 Highway 111
Rancho Mirage, California, 92270
Em: [email protected]
(760) 328-2266 Ext. 253
RE: March 27, 2023, Architectural Review Board Meeting — City of Rancho Mirage's Ritz -Carlton Phase II Expansion Project (Agenda Item No. 1).
Dear Mr. Torres:
On behalf of the Southwest Mountain States Regional Council of Carpenters ("SWMSRCC"), my Office is submitting these comments for the City of Rancho Mirage's ("City" or "Lead Agency") March 27, 2023, Architectural Review Board ("ARB") meeting for the Ritz -Carlton Phase II Expansion Project (Case Nos. EA21- 0002, GPZMA21-0001, DA21-0002, MOD21-0004) ("Project").
The Project involves the construction of the Ritz -Carlton Residences Rancho Mirage on a 35.07 -acre site located at 68900 Frank Sinatra Drive, Rancho Mirage, CA 92270 (APNs: 689-330-026, -028, -032, -034; 689-020-012, -014; 689-331-001, -018) in Riverside County. Nestled in the foothills of the Santa Rosa Mountains 650 feet above the Coachella Valley below, the 150,000 -square -foot Project will consist of a one -to three-story apartment and condominium complex, along with a parking garage, hotel, 28,843 square feet of event space, 6,273 square feet of restaurant space, and 5,513 square feet for amenities. The Project Site includes an existing hotel that opened as a Ritz -Carlton in 1988 and was later rebranded. The Project would provide a total of 106 units and 381 vehicle parking spaces.
SWMSRCC is a labor union representing over 63,000 union carpenters in 10 states, including California, and has a strong interest in well -ordered land use planning and in addressing the environmental impacts of development projects. Some SWMSRCC 5015
City of Rancho Mirage — Ritz -Carlton Phase II Expansion March 27, 2023
members live, work, and recreate in the City and the surrounding communities and would be directly affected by the Project's environmental impacts.
SWMSRCC expressly reserves the right to supplement these comments at or prior to hearings on the Project, and at any later hearing and proceeding related to this Project.
Gov. Code, § 65009(b); PRC, § 21177(a); see Bakersfield Citizens for Local Control v.
Bakersfield (2004) 124 Cal.App.4th 1184, 1199-1203; see also Galante Vineyards v.
Monterey Water Dist. (1997) 60 Ca1.App.4th 1109, 1121.
SWMSRCC incorporates by reference all comments raising issues regarding the Project and its environmental review and associated documents and reports (including the City's Staff Report), or lack thereof. See Citizens for Clean Energy v. City of Woodland (2014) 225 Ca1.App.4th 173, 191 (finding that any party who has objected to the project's environmental documentation may assert any issue timely raised by other parties).
Moreover, SWMSRCC requests that the City provide notice for any and all notices referring or related to the Project issued under CEQA (PRC, § 21000 et seq.), and the California Planning and Zoning Law ("Planning and Zoning Law") (Gov. Code, §§ 65000-65010). California Public Resources Code, sections 21092.2 and 21167, subsection (f) and California Government Code, section 65092 require agencies to mail such notices to any person who has filed a written request for them with the clerk of the agency's governing body.
I. THE CITY SHOULD REQUIRE THE USE OF A LOCAL
WORKFORCE TO BENEFIT THE COMMUNITY'S ECONOMIC
DEVELOPMENT AND ENVIRONMENT.
The City should require that the Project be built using local workers who have graduated from a Joint Labor -Management Apprenticeship Program approved by the State of California, have at least as many hours of on-the-job experience in the applicable craft which would be required to graduate from such a program, or are registered apprentices in such a program.
Community benefits such as local hire can also be helpful to reduce environmental impacts and improve the positive economic impacts of the Project. Local hire provisions requiring that a certain percentage of workers reside within 10 miles or less of the Project site can reduce the length of vendor trips, reduce greenhouse gas 5016
City of Rancho Mirage — Ritz -Carlton Phase II Expansion March 27, 2023
emissions, and provide localized economic benefits. As environmental consultants Matt Hagemann and Paul E. Rosenfeld note:
[A]ny local hire requirement that results in a decreased worker trip length from the default value has the potential to result in a reduction of construction -related GHG emissions, though the significance of the reduction would vary based on the location and urbanization level of the project site.
March 8, 2021, SWAPE Letter to Mitchell M. Tsai re Local Hire Requirements and Considerations for Greenhouse Gas Modeling.
Workforce requirements promote the development of skilled trades that yield sustainable economic development. As the California Workforce Development Board and the University of California, Berkeley Center for Labor Research and Education concluded:
[L]abor should be considered an investment rather than a cost —and investments in growing, diversifying, and upskilling California's workforce can positively affect returns on climate mitigation efforts. In other words, well -trained workers are key to delivering emissions reductions and moving California closer to its climate targets.1
Furthermore, workforce policies have significant environmental benefits given that they improve an area's jobs -housing balance, decreasing the amount and length of job commutes and the associated greenhouse gas ("GHG") emissions. In fact, on May 7, 2021, the South Coast Air Quality Management District found that that the "[u] se of a local state -certified apprenticeship program" can result in air pollutant reductions.' Locating jobs closer to residential areas can have significant environmental benefits.
As the California Planning Roundtable noted in 2008:
California Workforce Development Board (2020) Putting California on the High Road: A Jobs and Climate Action Plan 2030 at p. ii, available at https://laborcenter.berkeley.edu/ wo-content/u?loads/2020/09 /Putting-California-on-the-High-Road.Sdf. 2 South Coast Air Quality Management District (May 7, 2021) Certify Final Environmental Assessment and Adopt Proposed Rule 2305 — Warehouse Indirect Source Rule — Warehouse Actions and Investments to Reduce Emissions Program, and Proposed Rule 316 — Fees for Rule 2305, Submit Rule 2305 for Inclusion Into the SIP, and Approve Supporting Budget Actions, available at http:/ /www.ac md.gov/docs/default- source /Agendas/ Governing -Board /2021 /2021-May7-027.pdf?sfvrsn=10. 5017
City of Rancho Mirage — Ritz -Carlton Phase II Expansion March 27, 2023
People who live and work in the same jurisdiction would be more likely to take transit, walk, or bicycle to work than residents of less balanced communities and their vehicle trips would be shorter. Benefits would include potential reductions in both vehicle miles traveled and vehicle hours traveled.3
Moreover, local hire mandates and skill -training are critical facets of a strategy to reduce vehicle miles traveled ("VMT"). As planning experts Robert Cervero and Michael Duncan have noted, simply placing jobs near housing stock is insufficient to achieve VMT reductions given that the skill requirements of available local jobs must match those held by local residents.4 Some municipalities have even tied local hire and other workforce policies to local development permits to address transportation issues. Cervero and Duncan note that:
In nearly built -out Berkeley, CA, the approach to balancing jobs and housing is to create local jobs rather than to develop new housing. The city's First Source program encourages businesses to hire local residents, especially for entry- and intermediate -level jobs, and sponsors vocational training to ensure residents are employment -ready. While the program is voluntary, some 300 businesses have used it to date, placing more than 3,000 city residents in local jobs since it was launched in 1986. When needed, these carrots are matched by sticks, since the city is not shy about negotiating corporate participation in First Source as a condition of approval for development permits.
Recently, the State of California verified its commitment towards workforce development through the Affordable Housing and High Road Jobs Act of 2022, otherwise known as Assembly Bill No. 2011 (AB2011). AB2011 amended the Planning and Zoning Law to allow ministerial, by -right approval for projects being built alongside commercial corridors that meet affordability and labor requirements. 3 California Planning Roundtable (2008) Deconstructing Jobs -Housing Balance at p. 6, available at https://cproundtable.org/static/media/uploads/publications/cpr-jobs- housing..pdf
4 Cervero, Robert and Duncan, Michael (2006) Which Reduces Vehicle Travel More: Jobs - Housing Balance or Retail -Housing Mixing? Journal of the American Planning Association 72 (4), 475-490, 482, available athtt?://reconnectingamerica.org/assets/USloads/UTCT- 825.df.
5018
City of Rancho Mirage — Ritz -Carlton Phase II Expansion March 27, 2023
The City should consider uti i7ing local workforce policies and requirements to benefit the local area economically and to mitigate GHG emissions, improve air quality, and reduce transportation impacts.
II. THE CALIFORNIA ENVIRONMENTAL QUALITY ACT.
A. Background Concerning Environmental Impacts Reports.
The California Environmental Quality Act is a California statute designed to inform decision -makers and the public about the potential significant environmental effects of a project. CEQA Guidelines, § 15002(a)(1).5 At its core, its purpose is to "inform the public and its responsible officials of the environmental consequences of their decisions before they are made." Citizens of Goleta Valley v. Board of Supervisors (1990) 52 Ca1.3d 553, 564.
CEQA directs public agencies to avoid or reduce environmental damage, when possible, by requiring alternatives or mitigation measures. CEQA Guidelines, 15002(a) (2)-(3); see also Berkeley Keep Jets Over the Bqy Committee v. Board of Port Comes (2001) 91 Ca1.App.4th 1344, 1354; Citizens of Goleta Valley v. Board of Supervisors (1990) 52 Ca1.3d 553; Laurel Heights Improvement Assn., 47 Ca1.3d at p. 400. The EIR serves to provide public agencies and the public in general with information about the effect that a proposed project is likely to have on the environment and to "identify ways that environmental damage can be avoided or significantly reduced." CEQA Guidelines, § 15002, subd. (a)(2). If the project has a significant effect on the environment, the agency may approve the project only upon finding that it has "eliminated or substantially lessened all significant effects on the environment where feasible" and that any unavoidable significant effects on the environment are "acceptable due to overriding concerns" specified in Public Resources Code section 21081. See CEQA Guidelines, §§ 15092, subds. (b)(2)(A)-(B).
While the courts review an EIR using an `abuse of discretion' standard, the reviewing court is not to uncritically rely on every study or analysis presented by a project proponent in support of its position. Berkeley Jets, 91 Cal.App.4th at p. 1355 (quoting Laurel Heights Improvement Assn., 47 Ca1.3d at pp. 391, 409 fn. 12) (internal quotations 5 The CEQA Guidelines, codified in Title 14 of the California Code of Regulations, section 15000 et seq., are regulatory guidelines promulgated by the state Natural Resources Agency for the implementation of CEQA. PRC, § 21083. The CEQA Guidelines are given "great weight in interpreting CEQA except when . . . clearly unauthorized or erroneous." Center for Biological Diversity v. Dept. of Fish & W7ildl fe (2015) 62 Ca1.4th 204, 217. 5019
City of Rancho Mirage — Ritz -Carlton Phase II Expansion March 27, 2023