Rancho Mirage City Council
December 18, 2025

TRANSIT NOISE AND VIBRATION IMPACT ASSESSMENT MANUAL
The following considerations can assist in determining circumstances that trigger the need for mitigation and include examples of how they can be applied in a noise mitigation policy:
• Number of Noise -Sensitive Sites Affected
A row or cluster of residences adjacent to a rail transit line establishes a greater need for mitigation than one or several isolated residences in a mixed -use area. Single residences may not be able to meet a cost- effectiveness criterion for mitigation.

Example Mitigation Policy Consideration: Set a minimum number of noise -sensitive sites as a threshold, combined with a reference to a cost- effectiveness criterion.
• Increase over Existing Noise Levels
Since the noise impact criteria are delineated as bands or ranges, project noise can vary 5 to 7 decibels (dB) within the band of moderate impact at any specific ambient noise level. If the project and ambient noise plot falls just below the severe range, the need for mitigation is strongest for a moderate impact. Similarly, if the plot falls within the moderate range just above the no impact threshold, the impacts are expected to be less, so the justification for mitigation would not be as strong.

Example Mitigation Policy Consideration: Set a strong need for mitigation when a moderate impact is 2 dB (for example) over the no impact threshold.
• Noise Sensitivity of the Property
Section 4. I includes a comprehensive list of noise -sensitive land uses, yet there can be differences in noise sensitivity depending on individual circumstances. For example, parks and recreational areas vary in their sensitivity depending on the type of use they experience (active vs. passive recreation) and the settings in which they are located.

Example Mitigation Policy Consideration: Cite the use of the property as a determination of sensitivity for parks and recreational areas. • Effectiveness of the Mitigation Measure(s)
Determine the magnitude of the noise reduction that can be achieved, and consider whether there are conditions that limit effectiveness, such as noise barrier effectiveness for a multi -story apartment building.

Example Mitigation Policy Consideration: Set a minimum reduction in noise level to be considered effective. A 5 -dB reduction is typically considered an effective reduction from mitigation.
• Feasibility of the Mitigation Measure(s)
Determine if the mitigation measure is feasible from an engineering, operations or safety perspective. In some cases, it may not be possible to construct mitigation (noise barriers) due to physical or structural limitations FEDERAL TRANSIT ADMINISTRATION 6
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or because of safety concerns, especially related to sight lines for pedestrians and vehicles.

Example Mitigation Policy Consideration: State that the engineering design of the mitigation must be feasible, that it must be implementable in light of operations, and that mitigation must not compromise safety. • Fairness and Equity of the Mitigation Measure(s)
Ensure that mitigation measures are applied in a fair and equitable manner.

In many cases, small differences in distances or operations can result in small differences in projected noise levels. For example, all the residences in a row could have a projected moderate impact except for one residence at the end of the row that falls just under the moderate criteria due to being set slightly further back from the alignment. In a case like this, mitigation should be applied for the entire row of residences if possible.

Example Mitigation Policy Consideration: State that mitigation should be applied equitably.
• Existing Transportation Noise
Neighborhoods with ambient noise levels already heavily influenced by transportation noise, especially the same type of noise source as the project, should be considered. Often adding a new similar noise source will not add to the ambient noise levels or only slightly increase it to within acceptable levels. Whereas, impacts would be more likely, if the new noise was added to a neighborhood with minimal transportation noise. However, it is important to note that per (Section 4. I, Step 3) the higher the existing noise, the lower the allowable noise increase from new sources. A new cumulative noise environment may be very objectionable because people will not be compartmentalizing the existing noise versus the new noise and reacting only to the new noise. In this circumstance, impacts predicted in the moderate range could be treated as if they were severe.

Example Mitigation Policy Consideration: Set a policy that moderate impacts under these circumstances be treated as severe and cite the potential for reducing noise from existing transportation noise, as well as from project noise.
• Community Views
This manual provides the methodology to make an objective assessment of the need for noise mitigation. However, the views of the community should be considered where there are potential noise impacts predicted through this manual. The NEPA compliance process provides the framework for hearing the community's concerns about a proposed project and then making a good -faith effort to address those concerns. Many projects can be expected to have projected noise levels within the moderate impact range and, where possible, decisions regarding mitigation should be made after considering input from the affected public, relevant government agencies, and community organizations. There have been cases where the solution to the noise problem, a noise barrier, was not preferable to community members because of perceived adverse visual effects.

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Example Mitigation Policy Consideration: State that community input in determining the need for mitigation will be included whenever possible. • Implementation Cost
Cost is an important consideration in reaching decisions about noise mitigation measures. One guideline for gauging the reasonableness of the cost of mitigation is the state DOT's procedures on the subject. Many states have established their own cost threshold per benefited residence for determining whether installation of noise barriers for noise reduction is a reasonable expenditure. Several airport authorities have placed limits on the costs they will incur for sound insulation per residence for homes, and FTA assesses cost in a similar manner by benefited residence. Higher costs may be justified depending on the specific set of circumstances of a project.

Example Mitigation Policy Consideration: State the adopted cost threshold per benefited receiver for typical circumstances. 01-31
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SECTION Transit Noise
3 Source
MUM
This section presents the basic concepts of transit noise as background for computation methods and transit noise assessment procedures presented in Section 4. An overview of fundamental noise topics, including amplitude, frequency, time pattern, and decibel addition, is presented in Appendix B.

The Source -Path -Receiver framework for noise illustrated in Figure 3-I is central to all environmental noise studies. Each transit source generates noise that depends upon the type of source and its operating characteristics. Along the propagation path, between all sources and receivers, noise levels can be reduced (attenuated) by distance depending on ground type, intervening obstacles, and other factors. Finally, noise combines from multiple sources at each receiver and potentially interferes with activities at that location.

Path Receiver
Figure 3- I Source -Path -Receiver Framework
This section contains the following:
• Section 3. I presents the noise metrics used in this manual. • Section 3.2 provides an overview of transit noise sources, including a listing of major sources and a discussion of noise -generation mechanisms.
■ Section 3.3 provides an overview of noise paths, including a discussion of the various attenuating mechanisms on the path between source and receiver.
■ Section 3.4 provides an overview of receiver response to transit noise, including a discussion of the technical background for transit noise criteria and the distinction between absolute and relative noise impact.

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3.1 Noise Metrics
This manual uses the noise metrics outlined in Table 3- I for transit noise measurements, computations, and assessment. The terminology is consistent with common usage in the United States. All of these noise metrics are expressed in units of A -weighted decibels (dBA). A -weighted sound levels represent the overall noise at a receiver that is adjusted in frequency to approximate typical human hearing sensitivity. This is the basic noise unit for transit noise analyses.

Table 3-I Noise Metrics
Metric
Abbreviation
Definition
A -weighted Sound Level
dBA
A -weighted sound levels represent the overall noise at a receiver that is adjusted in frequency to approximate typical human hearing sensitivity. This is expressed as A -weighted decibels (dBA), the basic noise unit for transit noise analyses.

Sound Exposure Level
SEL
SEL is the cumulative noise exposure from a single noise event, normalized to one second. 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 is an intermediate metric in the measurement and calculation of both Le,(,) and Lde.

Equivalent Sound Level
Leq()
The equivalent sound level Len(t) describes a receiver's cumulative noise exposure from all events normalized to a specified period of time "t". Lqo 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 transit noise impact assessments, the equivalent sound level metric is A -weighted and all events are normalized over a one -hour time period, Leq(inr). For transit noise assessments, this metric is appropriate for non-residential land uses and is computed for the loudest hour of project related activity during hours of noise sensitivity.

Day -Night Sound Level
Lan
Ldn describes a receiver's cumulative noise exposure from all events over 24 hours. Events between 10 p.m. and 7 a.m. are increased by 10 dB to account for humans' greater nighttime sensitivity to noise. Len is used to assess transit noise for residential land uses.

Maximum Sound Level
La.

The maximum level describes the maximum noise level reached during a single noise event. For transit noise impact assessments, it is appropriate to consider the A -weighted maximum level (L,ne„ ) to understand the full context of the scenario. It is not appropriate to use this metric for transit noise impact assessments. This metric is commonly used in vehicle noise specifications and commonly measured for individual vehicles.

The noise metrics, including their application to transit noise and vibration impact assessment, are described in more detail in Appendix B.I.4. Mathematical definitions and graphic illustrations are presented to facilitate understanding and the interrelationships among metrics.

3.2 Sources of Transit Vehicle Noise
This section discusses major characteristics of the sources of transit noise.

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vehicles, and fixed -transit facilities. Procedures for computing nearby noise levels for major sources as a function of operating parameters such as vehicle speed are given in Sections 4.4 and 4.5.

Transit Vehicles in Motion
Transit vehicles most noticeably create noise when in motion. Noise from transit vehicles in motion can come from multiple sources, including the propulsion unit (i.e., the engine and engine components), the interaction of the wheels and/or tires and the running surface, and warning bells and horns.

Vehicle propulsion units generate:
• Whine from electric control systems and traction motors that propel rapid transit cars
• Diesel -engine exhaust noise from both diesel-electric locomotives and transit buses
• Air -turbulence noise generated by cooling fans
• Gear noise
Noise is also generated by the interaction of wheels and/or tires with their running surfaces. Tire noise from rubber -tired vehicles is generated at normal operating speeds. The interaction of steel wheels and rails generates:
• Rolling noise due to continuous rolling contact
Impact noise when a wheel encounters a discontinuity in the running surface such as a rail joint, turnout or crossover (where the train or rail vehicle switches off one track and onto another)
Impact noise from the wheel and running surface if the wheel is not completely round (wheel flat) or if the running surface is not completely flat
• Squeal generated by friction between wheels and rail on tight curves Transit vehicles are equipped with horns and bells for use in emergency situations and as a general audible warning to track workers and trespassers within the ROW, pedestrians, and motor vehicles at highway grade crossings.

Horns and bells on the moving transit vehicle combined with stationary bells at - grade crossings can generate high noise levels for nearby residents and are often sources of complaints.

For many noise sources, such as transit vehicles, the sound level is dependent on the speed of the noise source. In other cases, such as for stationary sources or horns mounted on vehicles, the sound level is not dependent on speed.

Figure 3-2 illustrates sound level dependence on speed for a diesel -powered commuter rail train and an electric -powered transit train assuming all other parameters, such as weight, are equal. Plotted vertically in this figure is a notional indication of the maximum sound level during a passby. Speed dependence is strong for electric -powered transit trains because wheel/rail noise is the dominant noise source and noise from this type of source increases strongly with speed. Diesel -powered commuter rail train noise is dominated by the locomotive exhaust noise at slower speeds. As speed increases, wheel -rail

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noise becomes the dominant noise source and diesel- and electric -powered trains generate similar noise levels. Similarly, speed dependence is also strong for automobiles, city buses (two -axle), and non -accelerating highway buses (three -axle), because tire/pavement noise is the dominant noise source for these vehicles. Accelerating highway bus noise is dominated by exhaust noise.

Commuce onvjeR d
Train Speed
Figure 3-2 Sound Level Dependence on Speed
Sound levels close to the source are also dependent on vehicle acceleration, vehicle length, running surface type, and running surface condition. For high- speed rail vehicles (vehicles with an operating speed of 90-250 mph are typically beyond the scope of this manual), air turbulence can also be a source of noise.

In addition, for an elevated structure, the guideway can radiate noise as it vibrates in response to the dynamic loading of the moving vehicle.

Stationary Transit Vehicles
Noise can be generated by transit vehicles even when they are stationary. For example, auxiliary equipment such as cooling fans on motors, radiator fans, plus hydraulic, pneumatic, and air-conditioning pumps, often continue to run when vehicles are stationary. Transit buses are also often left idling in stations or storage yards.

Fixed -transit Facilities
Noise can also be generated by sources at fixed -transit facilities. Such sources include ventilation fans in transit stations, subway tunnels, and electric power substations, as well as equipment in chiller plants, and many activities within maintenance facilities and shops.

Common Noise Sources
Table 3-2 summarizes common sources of transit noise by vehicle and facility type.

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Table 3-2 Sources of Transit Noise
Vehicle or Facility*
Dominant Components Comments
RRT or Light Rail Transit
(LRT) on exclusive ROW
Wheel/rail interaction and
guideway amplification
Depends on condition of wheels and rails
Propulsion system
When accelerating and at higher speeds
Brakes
When stopping
Auxiliary equipment
When stopped
Wheel squeal
On tight curves
In general
Noise increases with speed and train length
LRT in Mixed Traffic
Wheel squeal
On tight curves
Auxiliary equipment
When stopped
Horns and crossing bells
At -grade crossings and stations
In general
Traveling at lower speeds in mixed traffic
produces less noise than when traveling at
higher speeds in exclusive ROW
Commuter Rail
Diesel exhaust
On diesel -hauled trains
Cooling fans
On both diesel and electric -powered trains
Wheel/rail interaction
Depends on condition of wheels and rails
Horns and crossing gate bells
At -grade crossings and stations
In general
Noise is usually dominated by locomotives and
horns/bells at -grade crossings
Low and Intermediate
Capacity Transit
Propulsion systems, including
speed controllers
At low speeds
Ventilation systems
At low speeds
Tire/guideway interaction
For rubber -tired vehicles, including monorails
Wheel/rail interaction
Depends on condition of wheels and rails
In general
Wide range of vehicles: monorail, rubber -
tired, steel -wheeled, linear induction. Noise
characteristics depend upon type
Diesel Buses
Cooling fans
While idling
Engine casing
While idling
Diesel exhaust
At low speeds and while accelerating
Tire/roadway interaction
At moderate and high speeds
In general
Includes city buses (generally two -axle) and
commuter buses (generally three -axle)
Electric Buses and
Trackless Trolleys
Tire/roadway interaction
At moderate speeds
Electric traction motors
At moderate speeds
In general
Much quieter than diesel buses
Bus Storage Yards
Buses starting up
Usually most disruptive in the early morning
Buses accelerating
Usually near entrances/exits and/or locations
that require buses to accelerate (tight turns)
Buses idling
Warm-up areas
In general
Site specific: often peak periods with
considerable noise
Rail Transit Storage Yards
Wheel squeal
On tight curves
Wheel impacts
On joints and switches
Wheel rolling noise
On tangent track
Auxiliary equipment
Throughout day and night; includes air -break
release noise
Coupling/uncoupling
On storage tracks
Signal horns
Throughout yard site
In general
Site specific: often early morning and peak
periods with considerable noise
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Maintenance Facilities
Signal horns
Throughout facility
Intercoms
Throughout facility
Impact tools
Shop buildings
Car/bus washers/driers
Wash facility
Vehicle activity
Throughout facility
In general
Site specific: considerable activity throughout
day and night, some outside.

Stations
Automobiles
Patron arrival/departure, especially in early
morning
Buses idling
Bus loading zone
Intercoms
Platform area
Locomotive idling
At commuter rail terminal stations
Auxiliary systems
At terminal stations and layover facilities
Horns
At stations, if applicable
In general
Site specific, with peak activity periods
Subways
Fans
Noise through vent shafts/structures
Buses/trains in tunnels
Noise through vent shafts/structures
In general
Noise is not a problem, except in the
immediate vicinity of vent shafts/structures.
* Refer to Appendix A for additional information.

3.3 Paths of Transit Noise from Source to
Receiver
This section contains a qualitative overview of noise -path characteristics from source to receiver, including attenuation along these paths. Equations for specific noise -level attenuations along source -receiver paths are included in Sections 4.4 and 4.5.

Sound paths from source to receiver are predominantly through the air. Along these paths, sound reduces with distance due to divergence, absorption/diffusion, and shielding. These mechanisms of sound attenuation are discussed below.

Divergence
Sound levels naturally attenuate with distance, as shown in Figure 3-3. The plot shows attenuation at the receiver relative to the sound level 50 ft from the source. This type of attenuation is called divergence and is dependent upon source configuration (line or point source) or other source -emission characteristics. Localized sources (point sources) grouped closely together attenuate greatly with distance at a rate of approximately 6 dB per doubling of distance. Examples of point sources include highway grade -crossing signals along rail corridors, intercoms in maintenance yards and other closely grouped sources of noise. Vehicles passing along a track or roadway forming a line are called line sources. Line sources attenuate less than point sources with distance.

Rate of attenuation for line sources varies depending on the noise metric. Leq(Ihr) and Ld„ noise levels attenuate at a rate of 3 dB per doubling of distance and Lma, noise levels attenuate at a rate of 3 to 6 dBs per doubling of distance.

Figure 3-3 illustrates approximate attenuation with distance between the source and receiver for point and line sources. The line source curve for the Lmax noise FEDERAL TRANSIT ADMINISTRATION 14
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metric separates into three curves because it is dependent on the length of the line source. Equations for the curves in Figure 3-3 are included in Section 4.5. 0 10
o
20 30
40 50 100 500
Source -receiver distance, in feet
1,000
Line Sources
Leo & Ldn
Lmax
Point Sources
Figure 3-3 Attenuation Due to Distance (Divergence)
Absorption/Diffusion
In addition to distance, sound levels can be attenuated depending on the type of ground between the source and receiver. A portion of the sound energy is absorbed by the ground and only the remaining energy travels to the source.

How much energy the ground absorbs is dependent on the ground type (characterized as acoustically "hard" or "soft") and geometry. Example absorptive ground types include freshly -plowed or vegetation -covered ground.

Figure 3-4 illustrates approximate attenuation due to ground type by source to receiver path distance and height. Ground attenuation can be as large as 5 dB over a path distance of several hundred ft. At very large distances, wind and temperature gradients could modify the expected ground attenuation. However, these variable atmospheric effects are not included in this manual because they generally occur beyond the range of typical transit -noise impact. Equations for the curves in this figure are included in Section 4.5.
m
c
o
Ts
2 t
10 50 100 500
Source -receiver distance, in feet
1,000
Figure 3-4 Attenuation due to Soft Ground
Shielding
Sound paths are sometimes interrupted by terrain, human -constructed noise barriers, rows of buildings, or other objects. Noise barriers are one of the most effective means of mitigating noise (Section 4.5, Step 7). A noise barrier reduces sound levels at a receiver by breaking the direct line -of -sight between source and receiver with a solid wall (in contrast to vegetation which hides the source from view but does not reduce sound levels substantially over short distances).

Sound energy reaches the receiver only by bending (diffracting) over the top of FEDERAL TRANSIT ADMINISTRATION I5
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the barrier, as shown in Figure 3-5. This diffraction over the barrier reduces the sound level that reaches the receiver. One important consideration in using noise barriers to mitigate noise impacts is safety. Noise barriers, if not designed and sited carefully, can reduce visibility of trains for pedestrians and motorists, leading to less safe conditions. It is important to consult with safety experts when choosing and siting a noise barrier.

Noise barriers for transportation systems are typically used to attenuate noise at the receiver, potentially reducing received sound levels by 5 to 15 dB, depending upon barrier height, length, and distance from both source and receiver. Barriers on structures close to the transportation noise source may provide less attenuation than barriers located farther from the source due to reverberation (multiple reflections) between the barrier and the body of the vehicle or noise source. This reverberation can be offset by increased barrier height and/or acoustical absorption on the source side of the barrier. Further discussion and equations on acoustical absorption and barrier attenuation is provided in Section 4.5.

Source -to -receiver sound paths may not always travel through the air, but rather through the ground or through structural components of the receiver's building. Discussion of such ground -borne and structure -borne propagation is included in Section 5.

Rail car
Barrier A
L Barrier
without absorption
Sound
Shadow
L Barrier
with absorption
Figure 3-5 Noise Barrier Geometry

3.4 Receiver Response to Transit Noise
This section contains an overview of human receiver response to noise. It serves as background information for the noise impact criteria in Section 4. I .

Noise can interrupt ongoing activities causing community annoyance, especially in residential areas. In general, most residents become highly annoyed when noise interferes considerably with activities such as sleeping, talking, noise - sensitive work, and audio entertainment. In addition, some land uses, such as outdoor concert pavilions, are inherently incompatible with high noise levels.

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Annoyance from noise has been investigated and approximate dose -response relationships have been quantified by the U.S. Environmental Protection Agency (EPA).(5) The selection of noise metrics in this manual is largely based upon this EPA work. Beginning in the I970s, the EPA undertook a number of research and synthesis studies relating to community noise of all types. Results of these studies have been widely published, discussed, and refereed by many professionals in acoustics. Basic conclusions of these studies have been adopted by the Federal Interagency Committee on Noise (FICON),(ii1 the U.S.

Department of Housing and Urban Development (HUD), the American National Standards Institute, and even internationally(6)(7)(8)(9) Conclusions from this seminal EPA work remain scientifically relevant today.

Figure 3-6 contains a synthesis of actual case studies of community reaction to newly introduced sources of noise in a residential urban neighborhood.('°) Plotted horizontally in the figure is the increase in noise from new sources above existing noise levels expressed as Day -Night Sound Levels, Ldn, discussed in Appendix B.I.4.5. Plotted vertically is the community reaction to this newly introduced noise. As shown in the figure, community reaction varies from no reaction to vigorous action for newly introduced noises averaging from I 0 dB below existing to 25 dB above existing. Note the assumptions included in the graphic are associated with the specific data points from the study. These assumptions are generally appropriate to give context to most transit projects, but community reaction may differ for conditions specific to each project.

In many community attitudinal surveys, transportation noise has been ranked among the greatest causes of community dissatisfaction. A synthesis of many such surveys on annoyance is shown in Figure 3-7.(I X1(12) Noise exposure levels are plotted against the percentage of people who are highly annoyed by the particular level of neighborhood noise. As shown in the figure, the percentage of high annoyance is approximately 0 percent at 45 dB, I 0 percent around 60 dB, and increases quite rapidly to approximately 70 percent around 85 dB. The scatter about the synthesis line is due to community variation and wording differences in the surveys. An update of the original research containing additional railroad, transit and street traffic noise surveys generally follows the shape of the original response curve shown in Figure 3-7.(12)(13) As indicated by Figure 3-6 and Figure 3-7, introduction of certain levels of transit noise into a community may have two undesirable effects. First, it may substantially increase noise levels above existing noise levels in a community.

This effect is called a relative noise impact. Evaluation of this effect compares new noise levels to the existing levels. Criteria for a relative noise impact evaluation are based upon noise increases above existing levels. Second, newly introduced transit noise may interfere with community activities independent of existing noise levels. For example, it may be too loud to converse or sleep. This effect is called absolute noise impact and is expressed as a fixed level threshold that is not to be exceeded. The fixed level threshold is determined independently of existing noise levels. Relative and absolute noise impacts are discussed in terms of transit noise criteria in Section 4.1, Step 3.

The Federal Interagency Committee on Aviation Noise (FICAN) is the current version of this group.

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Community Reaction
Vigorous Action
Several threats
of legal action
or strong appeals
to local officials
to stop noise
Widespread complaints
or single threat
of legal action
Sporadic complaints
No reaction
although noise is
generally noticeable
Percentage of people highly annoyed
100
so
so
70 60
50 40
30 20
10 0
42 ■
■■ • ■
■

MMMMM MO MN

■ ■■ ■
Assumptions
Some prior exposure.

Windows partially open.

No pure tones or impulses.
-20 -10 0 10 20
Increase in noise from new sources above existings noise levels, Ldn Figure 3-6 Community Reaction to New Noise, Relative to Existing Noise in a Residential Urban Environment
50 60 70
Day -Night Sound Level, Ldn
80 90
Figure 3-7 Community Annoyance Due to Noise
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SECTION Noise Impact Analysis
4 The FTA noise impact analysis process is a multi -step process used to evaluate the project for potential noise impacts for FTA NEPA approvals. If impact is determined, measures necessary to mitigate adverse impacts must be considered for incorporation into the project.(4) It is recommended that project sponsors develop and formally adopt a policy for determining the need for mitigation for situations that are loosely covered by the impact criteria.

Considerations for mitigation policies are included in Section 2.3. The FTA noise impact analysis steps are summarized as follows and are described in the subsequent subsections:

4.1: Determine noise impact criteria.

Step I: Identify the type of project/dominant noise source (transit or multimodal).

Step 2: Choose land use category for FTA criteria.

4.2: Determine the highest appropriate level of noise analysis for the current stage of project planning or development.

4.3: Evaluate for the potential of impact according to the Noise Screening Procedure.

Step 1: Identify project type.

Step 2: Determine the screening distance.

Step 3: Identify the study area.

Step 4: Locate noise -sensitive land uses.

4.4: Evaluate impact according to the General Noise Assessment and evaluate preliminary mitigation options if impact is found.

Step I: Identify noise -sensitive receivers.

Step 2: Determine the project noise source reference levels.

Step 3: Estimate project noise exposure by distance.

Step 4: Combine noise exposure from all sources.

Step 5: Measure existing noise exposure.

Step 6: Inventory noise impacts.

Step 7: Determine noise mitigation needs.

4.5: Evaluate for impact according to the Detailed Noise Analysis and evaluate mitigation options if impact is found.

Step I: Identify noise -sensitive receivers.

Step 2: Determine noise source levels for detailed analysis.

Step 3: Calculate project noise exposure by distance.

Step 4: Combine noise exposure from all sources.

Step 5: Determine existing noise exposure.

Step 6: Assess noise impact.

Step 7: Determine noise mitigation measures.

In addition to analyzing for potential noise impacts, analyze the project for potential vibration impacts according to the process presented in Section 6.

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construction noise and vibration according to Section 7 and document findings according to Section 8.

4.1 Determine Noise Impact Criteria
This section describes the procedure for determining the appropriate criteria for assessing project noise impact based on the type of project and project noise source. Project noise is the new noise or change in noise introduced by the project. Noise impact criteria may vary for different segments of the project. Project segments can be portions of a project with similar characteristics.

The procedure to determine the appropriate impact criteria is described in this section and shown more simply as a flow chart in Figure 4-I. If there is uncertainty in how to determine the appropriate criteria, contact the FTA Regional office.

The selected criteria are used in the analysis procedures discussed in Sections

4.3, 4.4, and 4.5 to identify potential impacts and the level of impact.

Start
Yes/
"N,,, only? //
C•
Transit
Project
f N
Transit N No
V
(FTA criteria
& methods
V
\f/ Multi -modal
Project ,
Transit
N sources dominate Yes
-Nat all times?
\✓ FTA criteria
& methods
/H ighwaYNN
Nofsources dominate
• Nat all times?

FTA & FHWA
criteria & methods
Figure 4-I Noise Impact Criteria Flow Chart by Project Segment FEDERAL TRANSIT ADMINISTRATION 20
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Step I: Identify Project Type
Identify the type of project as transit, multimodal (transit and highway), or other multimodal according to the dominant noise source.

Option A: Transit Project (Transit Noise Only) — The transit project category includes all transit projects where the project noise is exclusively due to new transit sources, no changes are made to the highway or to existing highway noise barriers, and the existing noise levels generated by roadway sources will not change because of the project. For these transit projects, FTA is the lead agency conducting the environmental review in cooperation with the transit agency.

Typical examples of transit projects include:
• RRT, LRT, commuter rail, and AGT
• Rail projects built within an existing highway or railroad corridor that do not alter the existing noise levels generated by roadway sources • Bus facility projects with operations on local streets and highways used to access the facility, where the project does not include roadway construction or modification that changes roadway capacity substantially • Fixed facilities including storage and maintenance yards, passenger stations and terminals, parking facilities, and substations • Portions of transit projects not adjacent to highway corridors FTA impact criteria are appropriate for transit projects, proceed to Step 2.

Option B: Multimodal Project (Transit and Highway Noise) — In this manual, "multimodal" refers to projects that include changes to both transit and highway components, resulting in project noise comprised of both highway and transit noise sources.

Typical examples of multimodal projects include:
• New highway construction providing general-purpose lanes as well as dedicated bus and high occupancy vehicle (HOV) lanes
• Rail transit projects that involve changes to the highway travel lanes or existing highway noise barriers
Evaluate multimodal projects for impact according to the project noise source by project segment. FHWA's noise assessment methods are used to inform FTA's NEPA evaluation only for segments where highway noise levels change due to the transit project. These projects are not necessarily subject to FHWA's procedures at 23 CFR part 772 (see call out box below). For segments of the project outside the highway corridor, use FTA's criteria and methods. Use Table 4-I to determine multimodal project noise.

Once the project noise source(s) is identified, determine the appropriate assessment method according to Table 4-2.

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Note that a separate noise analysis may be required for FHWA approval of a multimodal project pursuant to 23 CFR part 772. For these projects, it is important to work with FHWA early in the environmental review process to determine how a noise assessment will be completed where FHWA approval is needed for the project.

The determination of whether a project is subject to FHWA procedures at 23 CFR part 772 depends upon the specific circumstances of a project. A proposed transit project that would share an existing highway ROW is not necessarily a FHWA-defined multimodal project. A transit project that meets all three of the following criteria is not considered a multimodal project subject to 23 CFR part 772:
• FTA is the lead agency in the NEPA process and FHWA's limited participation is as a cooperating agency.
• The main transportation purpose of the project, as stated in the purpose and need statement of the environmental document, is transit -related and not highway -related. • No Federal -aid highway funds are being used to fund the project.

Table 4-I Multimodal Project Noise Factors
Factor
Description
Volume of
Traffic
Major freeways and interstate highways often carry large volumes of traffic throughout the day and night such that the highway noise dominates at all times. Transit noise in this case may be unimportant by comparison, but must still be evaluated using FTA's noise criteria for a potential impact.

Traffic Patterns
Some highways and arterials serve primarily as commuter routes such that nighttime traffic diminishes considerably, while transit systems continue to operate well into the late hours. Here the dominant noise source at times of maximum sensitivity may be transit.

Type of Traffic
Some highways and arterials may serve commuters during the daytime hours, but provide access to business centers by trucks at night. In this case, the roadway noise would likely continue to dominate.

Alignment
Configuration
Elevation of the transit mode in the median or beside a busy highway may result in transit noise contributing more noise to nearby neighborhoods than a highway that may be partially shielded by rows of buildings adjacent to the ROW. In this case, both transit and highway noise may be considered dominant.

Table 4-2 Multimodal Project Assessment Methods
Dominant
Noise Source
Assessment Method
Transit, at
All Times
Use FTA criteria and methods. Proceed to Step 2.

Highway, at
All Times
Use FHWA criteria and methods to inform FTA's NEPA evaluation. Contact FHWA directly for assistance using FHWA noise analysis methods and FHWA noise impact criteria.

Transit and
Highway at
Different Times
Use both the FHWA and FTA methods to determine if one, both, or neither method determines impact due to the project noise for these segments. Note that the project noise includes both highway and transit sources associated with the project. Both methods are used because the FTA methods consider nighttime sensitivity while the FHWA methods consider the peak traffic hour.

Proceed to Step 2 for FTA criteria. Contact FHWA directly for assistance using FHWA noise analysis methods and FHWA noise impact criteria.

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Option C: Other Multimodal Projects — For projects with components from other modes, contact the FTA Regional office. Additional information on high-speed rail vibration and noise can be found in the Federal Railroad Administration (FRA) "High -Speed Ground Transportation Noise and Vibration Impact Assessment" guidance manual.i14)
Step 2: Choose Land Use Category for FTA Criteria
Determine the appropriate noise -sensitive land use category for the project segment using Table 4-3 and the descriptions below then, proceed to Step 3. FTA criteria are presented by land use.

Table 4-3 Land Use Categories and Metrics for Transit Noise Impact Criteria Land Use
Category
Land Use
Type
Noise
Metric, dBA
Description of Land Use Category
High
Sensitivity
Outdoor
Leq(Ihr)*
Land where quiet is an essential element of its intended purpose. Example land uses include preserved land for
serenity and quiet, outdoor amphitheaters and concert
pavilions, and national historic landmarks with
considerable outdoor use. Recording studios and concert halls are also included in this category.
2 Residential
Outdoor Lai
This category is applicable all residential land use and buildings where people normally sleep, such as hotels and hospitals.
3 Institutional
Outdoor
Leq(Ihr)*
This category is applicable to institutional land uses with primarily daytime and evening use. Example land uses
include schools, libraries, theaters, and churches where it is important to avoid interference with such activities as speech, meditation, and concentration on reading
material. Places for meditation or study associated with cemeteries, monuments, museums, campgrounds, and
recreational facilities are also included in this category. * Lq(Ihr) for the loudest hour of project -related activity during hours of noise sensitivity.

Noise -sensitive land use categories are described in in order of sensitivity. Most commercial or industrial uses are not considered noise -sensitive because activities within these buildings are generally compatible with higher noise levels.

Business can be considered noise -sensitive if low noise levels are an important part of operations, such as sound and motion picture recording studios.

For residential land use (category 2), apply the noise criteria at the nearest facade of the occupied portion of the building, e.g., not at a garage or porch.

The residential criteria should be applied at locations with nighttime sensitivity.

For major noise -sensitive outdoor use at non-residential locations, apply the noise criteria at the point of noise -sensitive use nearest the noise source.

Land use categories are evaluated using noise metrics that reflect the noise - sensitive time of day:
• Categories I and 3 — The noise metric, Leq(Ihr) is used for all category I and 3 land uses where nighttime sensitivity is not a factor. Category 3 land uses are considered less noise -sensitive than category I land uses.

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related activity during which human activities occur at the noise - sensitive location. See Appendix B. I.4.4 for more information on this metric.
• Category 2 — The noise metric Ldn is a used for all category 2 land uses where nighttime sensitivity is a factor. This noise metric includes a 10 - dB penalty for nighttime noise. See Appendix B.l.4.5 for more information on this metric.

Land Use Categories: Special Cases
Historic sites, parks, indoor -only land use, and undeveloped land require special consideration. In addition to NEPA, noise impacts may need to be considered under other environmental laws such as Section 1061151 or Section 4(f).(16) Indoor -only use and undeveloped land should be evaluated on a case -by -case basis to determine noise sensitivity based on how each facility is used or the reason it is protected under the applicable requirement.

Historic Sites — Section 106 requires Federal agencies to evaluate potential effects from projects on historic properties. Per the regulations at 36 CFR part 80Q(17) historic properties are defined as any prehistoric or historic district, site, building, structure, or object included in, or eligible for the National Register of Historic Places (NRHP). An adverse effect determination under Section 106 is made when a project may alter, directly or indirectly, any of the characteristics of a historic property that qualify the property for inclusion in the National Register in a manner that would diminish the integrity of the property's location, design, setting, materials, workmanship, feeling, or association.

Under FTA environmental reviews, some structures may be evaluated as noise - sensitive resources per this noise manual and evaluated as historic properties under Section 106. However, because this manual and Section 106 regulations have different criteria for effect, identifying a severe noise impact for a structure under this manual does not necessarily mean there would be an adverse effect under Section 106. It is important to thoroughly document the characteristics of historic properties that qualify for inclusion in the NRHP for evaluation of effect under Section 106.

If a property, for example, is listed on the NRHP under criterion C because the structure possesses high artistic values, but lacks integrity of setting, feeling, or association, it is unlikely that a change in the noise environment would affect the features that qualify the property for listing or eligibility for inclusion in the NRHP.

In the assessment of effects on historic properties, consideration should be given to not just the proposed transit project, but any associated mitigation measures with the transit project. For example, if a transit project would involve noise walls or berms as mitigation, the effect of those structures on the visual setting may need to be considered in a Section 106 analysis.

Parks — Most parks used primarily for active recreation such as sports complexes and bike or running paths are not considered noise -sensitive.

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However, some parks (even some in dense urban areas) are primarily used for passive recreation such as reading, conversation, or meditation. These places, which may be valued as havens from the noise and rapid pace of everyday city life, are treated as noise -sensitive, and are included in land use category 3.

Consult the state or local agency with jurisdiction over the park on questions about how the park is used, and visit the park to observe its use, if possible.

Indoor -Only Use — The land use categories described in this section correspond with noise impact criteria that provide protection for both outdoor and indoor land uses. For locations where noise impact will be evaluated but there is no outdoor land use such as apartment buildings, hotels or upper levels of multi -story buildings, indoor criteria can be used. In these cases, the criterion for indoor noise levels from project sources is a Ldn of 45 dBA.(18) This criterion is consistent with the Federal Aviation Administration (FAA). See Section 4.5 for more information on how indoor criteria apply to noise mitigation consideration.

Undeveloped Land — Undeveloped land may also need to be considered for noise impact assessment and mitigation if plans are under way to develop the land for noise -sensitive use. The policy for considering such land for assessment and mitigation should be determined on a project -specific basis by the project sponsor in consultation with the FTA Regional office.

Step 3: Determine Appropriate FTA Criteria Presentation FTA criteria for noise impact were developed specifically for transit noise sources operating on fixed -guideways or at fixed facilities in urban areas. These criteria are based on well -documented research on human response to community noise and represent a reasonable balance between community benefit and project costs. These criteria do not reflect specific community attitudinal factors. See Appendix C for additional background information on the development of FTA noise criteria.

The criteria specify a comparison of future project noise with existing noise.

Note that projections of future noise exposure without the project (no -build scenario) are not included in this analysis. The criteria also consider land use which is an important factor that reflects noise sensitivity based on activity and time period of concern. The criteria are defined with the expectation that communities already exposed to high levels of noise can only tolerate a small increase. In contrast, if the existing noise levels are low, it is reasonable to allow a greater change in the community noise.

The levels of impact are described in Table 4-4. The criteria at which the levels of impact occur are presented in two ways depending on the relationship of project and existing noise sources.

If the project noise source is a new source of transit noise in the community, such as a new project in an area currently without transit, use the criteria as presented in Option A. If the project noise adds to or changes existing transit noise in the community, use the criteria as presented in Option B.

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Table 4-4 Levels of Impact
Level of Impact
Description
No Impact
Project -generated noise is not likely to cause community annoyance. Noise projections in this range are considered acceptable by FTA and mitigation is not required.

Moderate Impact
Project -generated noise in this range is considered to cause impact at the threshold of measurable annoyance. Moderate impacts serve as an alert to project planners for potential adverse impacts and complaints from the community. Mitigation should be considered at this level of impact based on project specifics and details concerning the affected properties.

Severe Impact
Project -generated noise in this range is likely to cause a high level of community annoyance. The project sponsor should first evaluate alternative locations/alignments to determine whether it is feasible to avoid severe impacts altogether. In densely populated urban areas, evaluation of alternative locations may reveal a trade-off of affected groups, particularly for surface rail alignments. Projects that are characterized as point sources rather than line sources often present greater opportunity for selecting alternative sites. This guidance manual and FTA's environmental impact regulations both encourage project sites which are compatible with surrounding development when possible. If it is not practical to avoid severe impacts by changing the location of the project, mitigation measures must be considered.

Option A: Project Noise Impact Criteria Presentation — The impact criteria presentation for evaluating existing noise independently to project noise is presented in this option.

The noise levels at which impacts occur are presented in Figure 4-2 and Table 4-5. Equations for the impact criteria are presented in Appendix C. If impact is determined, measures necessary to mitigate impacts are to be considered for incorporation into the project.(;)
Figure 4-2 presents the existing noise exposure on the horizontal axis and project noise on the vertical axis. Category I and 2 land uses have the same criteria for project noise and are on the primary vertical axis. Category 3 land use criteria are presented on the secondary vertical axis. Note that project noise for category I and 3 land uses is expressed as Leq(Inr),whereas project noise for category 2 land use is expressed as Lan. Also, note that project noise criteria are 5 dB higher for category 3 land uses in Figure 4-2 since these types of land use are less noise -sensitive than those in categories I and 2.

Note that for projects in locations with existing noise levels below 55 dBA, the project noise exposure is allowed some increase over the existing noise exposure before it is considered to cause impact. For category I and 2 land uses, the maximum project noise level to be considered to cause no impact is 65 dBA (Leq(Ihr) or Ldn) regardless of the existing noise. Note that no impact at 65 dBA aligns with other Federal agencies in that a Lan of 65 dBA is a standard limit for an acceptable living environment among some Federal agencies.(19) (20) Project noise levels above the top curve are considered to cause severe impact.

The upper limit of the severe impact range is 75 dBA for category I and 2 land uses. The upper limit of 75 dBA is associated with an unacceptable living environment. Project noise between the two curves is considered to have moderate impact on the community.

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The criteria are also tabulated in Table 4-5. Figure 4-2 and the equations that correspond with this figure in Appendix C are the precise definition of the criteria. The values in Table 4-5 can be used for illustrative purposes and should only be used if all numbers are rounded up to the nearest decibel. 80 75
a 70
-0 2
4J
gi - 65
OO
x x a
E t 60
▪ N
o 5
3 ,5
55 � v
of
a
50 45
40 Severe Impact
Moderate
Impact
No Impact
45 40 45 50 55 60 65 70 75 80
Existing Noise Exposure (dBA)
85 80
75 a
Ti
70 c2
am
x
65 w `o
m
� v
z
60 m v
a
55 50
Figure 4-2 Noise Impact Criteria for Transit Projects
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Table 4-5 Noise Levels Defining Impact for Transit Projects Existing
Noise
Exposure,
dBA
Project Noise Impact Exposure, dBA
Category I (Leq(iho) or 2 (Ldfl) Sites
Category 3 Sites (Leq(Ihr))
Leg( Ihr) or I-dn
No
Impact
Moderate
Impact
Severe
Impact
No
Impact
Moderate
Impact
Severe
Impact
58 63
44 58
63 45
58 63
46 59
64 47
59 64
48 59
64 49
59 64
50 59
64 51
60 65
52 60
65 53
60 65
54 61
66 55
61 66
56 62
67 57
62 67
58 62
67 59
63 68
60 63
68 61
64 69
62 64
69 63
65 70
64 65
70 65
66 71
66 67
72 67
67 72
68 68
73 69
69 74
70 69
74 71
70 75
72 71
76 73
71 76
74 72
77 75
73 78
76 74
79 77
74 79
>77
75 80
Option B: Cumulative Noise Impact Criteria Presentation The impact criteria presentation for evaluating existing noise to project noise cumulatively is presented in this option.

In certain cases, the cumulative form of the noise criteria shown in Figure 4-3 can be used. These cases involve projects where changes are proposed to an existing transit system, as opposed to a new project in an area previously without transit. Such changes might include operations of a new type of vehicle, modifications of track alignments within existing transit corridors, or changes in facilities that dominate existing noise levels. In these cases, the existing noise FEDERAL TRANSIT ADMINISTRATION 28
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sources change because of the project, and so it is not possible to define project noise separately from existing noise. An example would be a commuter rail corridor where the existing noise along the alignment is dominated by diesel locomotive -hauled trains, and where the project involves electrification with the resulting replacement of some of the diesel -powered locomotives with electric trains operating at increased frequency of service and higher speeds on the same tracks. In this case, the existing noise can be determined and a new future noise can be calculated, but it is not possible to describe what constitutes the "project noise." For example, if the existing noise dominated by trains was measured to be an Ld„ of 63 dBA at a particular location, and the new combination of diesel and electric trains is projected to be an Ldn of 65 dBA, the change in the noise exposure due to the project would be 2 dB. Referring to Figure 4-3, a 2 -dB increase with an existing noise exposure of 63 dBA would be rated as a moderate impact. Normally the project noise is added to the existing noise to come up with a new cumulative noise, but in this case, the existing noise was dominated by a source that changed due to the project, so it would be incorrect to add the project noise to the existing noise. Consequently, the existing noise determined by measurement is compared with a new calculated future noise, but a description of what constitutes the actual project is complex.

Another example would be a rail corridor where a track is added and grade crossings are closed, potentially resulting in a change in train location and horn operation. Here the "project noise" results from moving some trains closer to some receivers, away from others, and elimination of horns. In this case, the change in noise level is more readily determined than the noise from the actual project elements. In all cases, Figures 4-3 and 4-4 for changes in a transit system results in the same assessment of impact as Figure 4-2 for development of transit facilities in a new area.

The noise impact criteria in Figure 4-3 and Figure 4-4 are presented as an increase in cumulative noise level between the existing and project conditions.

The horizontal axis represents the existing noise exposure and the vertical axis is the increase in cumulative noise level due to the transit project. Note that noise exposure is expressed as Legl,hr)for category I and 3 land uses and Ldn for category 2 land use. Since Leg(,n,)and Ld„ are measures of total acoustic energy, any new noise sources in a community will cause an increase, even if the new source level is the same or less than the existing noise level (refer to decibel addition in Appendix B). As shown in Figure 4-3, the criterion for moderate impact is a noise exposure increase of I O dB for an existing noise exposure level of 42 dBA or less, but only a I -dB increase when the existing noise exposure is 70 dBA.

As the existing level of ambient noise increases, the allowable level of transit noise increases, but the total amount that community noise exposure is allowed to increase is reduced. This accounts for the unexpected result that a project exposure which is less than the existing noise exposure can still cause impact.

This is clearer from the examples listed in Table 4-6 which indicate the level of transit noise allowed for different existing levels of exposure. Any increase greater than shown in the table will cause moderate impact.

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20 15
c
10 o
a
5 o
z
Severe Impact
— Moderate
— Impact
0 40
No Impact
45 50 55 60 65 70 75 80
Existing Noise Exposure (dBA)
Metre: Category 1 - Leg(1h)
Category 2 - Ldn
Figure 4-3 Increase in Cumulative Noise Levels Allowed by Criteria (Land Use Cat. I & 2)
25 fb
a 20
N
to Moderate
i Impatt
-Severe, Impact
C
No Impact
Cs
W
w
5 -
0 75
40 45 50 55 60 65 70
Existing Noise Exposure (dBA)
Metric:Category 3 - Leq(1h)
80 Figure 4-4 Increase in Cumulative Noise Levels Allowed by Criteria (Land Use Cat. 3)
This table shows that as the existing noise exposure increases from 45 dBA to 75 dBA, the allowed project noise exposure increases from 51 dBA to 65 dBA.

However, the allowed increase in the cumulative noise level decreases from 7 dB to 0 dB (rounded to the nearest whole decibel). The justification for this is that people already exposed to high levels of noise should be expected to tolerate only a small increase in the amount of noise in their community. In contrast, if the existing noise levels are quite low, it is reasonable to allow a greater change in the community noise for the equivalent difference in annoyance.

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Note that Table 4-6 was developed for illustrative purposes and the official criteria are included in Figure 4-3 and Figure 4-4 and the associated equations.

Table 4-6 Noise Impact Criteria: Effect on Cumulative Noise Exposure Ld„ or Leq(Ihr) in dBA (rounded to nearest whole decibel) Existing
Noise
Exposure
Allowable Project
Noise Exposure
Before Moderate
Impact
Allowable
Combined Total
Noise Exposure
Allowable Noise
Exposure
Increase Before
Moderate Impact
45 51
52 7
50 53
55 5
55 55
58 3
60 57
62 2
65 60
66 I
70 64
71 I
75 65
75 0

4.2 Determine Noise Analysis Level
There are three levels of analysis to evaluate noise on a transit project based on the type and scale of the project, stage of project development, and environmental setting. These levels, described below, are the Noise Screening Procedure, the General Noise Assessment and the Detailed Noise Analysis.

The Noise Screening Procedure, conducted first, defines the study area of any subsequent noise impact assessment. Where there is potential for noise impact, the General Noise Assessment and Detailed Noise Analysis procedures are used to determine the extent and severity of impact. In some cases, a General Noise Assessment may be all that is needed. However, if the proposed project is near noise -sensitive land uses, and it appears at the outset that the impact would be substantial, it is prudent to conduct a Detailed Noise Analysis.

Conduct the noise screening procedure and then determine the appropriate noise analysis option.

Noise Screening Procedure — The Noise Screening Procedure is a simplified method of identifying study area receivers or locations where a project may have the potential for noise impacts from transit projects. This procedure accounts for impact criteria, the type of project, and noise -sensitive land uses. If no noise -sensitive land uses or receivers are present in the analysis area, then no further noise assessment is needed. If noise -sensitive receivers are identified, then proceed to conduct a General Assessment and/or a Detailed Assessment.

The Noise Screening Procedure steps are provided in Section 4.3.

General Noise Assessment — The General Noise Assessment is used to examine potentially impacted areas identified in the screening step by examining the location and estimated severity of noise impacts. This procedure considers noise source and land use information likely to be available at an early stage in the project development process. Estimates are made of project noise levels and of existing noise conditions to model the location of a noise impact contour FEDERAL TRANSIT ADMINISTRATION 31
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that defines the outer limit of an impact corridor or area. This modeling method uses transit -specific noise and adjustment data (in tabular and graphical form) for the noise computations.

For many smaller projects, this assessment may be sufficient to define impacts and determine whether noise mitigation is necessary. The procedure can be used in conjunction with established highway noise prediction procedures to compare highway, transit, and multimodal alternatives. If an assessment is needed to inform the decision on transit mode and general alignment in a corridor, the General Noise Assessment procedures should be used, and not the Detailed Noise Analysis, which requires more detailed information.

The General Noise Assessment procedure is provided in Section 4.4. FTA has also developed an Excel spreadsheet to more simply conduct the General Noise Assessment. It is on FTA's website at http://www.fta.dot.gov/ I2347_2233.html.

Detailed Noise Analysis — The Detailed Noise Analysis procedure is a comprehensive assessment method that produces the most accurate estimates of noise impacts for a proposed project. It is important to recognize that use of the Detailed Noise Analysis methods will not provide more accurate results than the General Noise Assessment unless more detailed and case -specific input data are used.

The project must be defined to the extent that location, alignment, transit mode, hourly operational schedules during day and night, speed profiles, plan and profiles of guideways, locations of access roads, and landform topography (including terrain and building features) are determined. A detailed Noise Analysis is often accomplished at the development of the final environmental impact statement (FEIS), record of decision (ROD), or combined FEIS/ROD in the NEPA process, when the preferred alternative is undergoing refinements to mitigate its adverse impacts. However, these project details may not be available until the final design phase, requiring that the detail noise analysis be conducted after the NEPA process is complete. However, it is recommended that the detailed analysis be conducted earlier for controversial projects or projects with highly noise -sensitive sites close to tracks.

A Detailed Noise Analysis may be warranted as part of the development of an environmental assessment (EA) if there are potentially severe impacts due to the proximity of noise -sensitive land uses.

In some cases, decisions on appropriate noise mitigation measures can be made based on the results of the General Noise Assessment. But if costly measures may be needed, it is generally recommended that a Detailed Noise Analysis be conducted to verify the need and design of the noise mitigation. The Detailed Noise Analysis is always appropriate under two sets of circumstances:
• For a major transit project with likely noise impacts after the preferred alternative has been selected.
• For any other transit project where potentially severe impacts are identified at an early stage.

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Noise impacts may occur for relatively minor transit projects when the project is near noise -sensitive sites, particularly residences. In this case, completing a Detailed Noise Analysis is recommended. Some examples include:
• A terminal or station sited adjacent to a residential neighborhood • A maintenance facility located near a school
• A storage yard adjacent to residences
• An electric substation located adjacent to a hospital The Detailed Noise Analysis procedure is provided in Section 4.5.

4.3 Evaluate Impact: Noise Screening Procedure
Identify the potential for impact using the Noise Screening Procedure described below.

Step I: Identify Project Type
Identify the project type using Table 4-7 and confirm the assumptions in Table 4-8 are appropriate for the project.

The noise screening procedure is intended to be conservative to broadly capture the potential for impact with minimal effort. To make the procedure conservative, the project system must be assumed to be operating under relatively high -capacity conditions, which would produce more noise than normal operating conditions. In addition, the assumptions in Table 4-8 were made using the lowest threshold of impact (50 dBA) from the criteria curves in Figure 4-2. Clarification can be obtained from FTA on special cases that are not represented in this section.

If the assumptions in Table 4-8 are not appropriate for the project, make adjustments to the screening distances in Table 4-8 according to the methodology in Section 4.4 or the FTA spreadsheet model.

Step 2: Determine the Screening Distance
Determine the appropriate screening distance considering the type of project and shielding from intervening buildings.
2a. Determine the appropriate screening distance column in Table 4-7.

Option A: Buildings in the Sound Paths — Use the screening distances in the "Intervening Buildings" column.

Option B: Buildings Not in the Sound Paths — Use the distances in the "Unobstructed" column.
2b. Adjust these distances according to the methodology in Section 4.4, or the FTA spreadsheet model, if the assumptions in Table 4-8 are not appropriate for the project. The appropriate screening distance is where the project noise reaches 50 dBA for the appropriate metric. If the assumptions in Table 4-8 are not appropriate for a commuter rail grade crossing project where horns and FEDERAL TRANSIT ADMINISTRATION 33
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warning bells are used, use the FRA horn noise model available from the FRA website to develop the screening distance distance (49 CFR § 222).(21) Step 3: Identify Study Area
Apply the screening distances as follows to identify the study area. The study area is intended to be sufficiently large to encompass all potentially impacted locations.

Option A: Fixed Guideway Transit Sources — Apply the screening distance from the guideway centerline.

Option B: Highway/Transit Sources (e.g., Bus) — Apply the screening distance from the nearest ROW line on both sides of a highway or access road.

Option C: Small Stationary Facilities — Apply the screening distance from the center of the noise -generating activity.

Option D: Stationary Facility Spread Over a Large Area — Apply the screening distance from the outer boundary of the proposed project site.

Step 4: Locate Noise -Sensitive Land Uses
Locate all noise -sensitive land uses within the study area using Table 4-3.

See Section 4.1 for more information on noise -sensitive land uses. Include all categories of noise -sensitive land uses in this step.

If no noise -sensitive land uses are identified, no further noise analysis is needed. If one or more of the noise -sensitive land uses are in the study area, proceed to Section 4.4 and complete a General Noise Assessment.

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Table 4-7 Screening Distance for Noise Assessments
Project Systems
Screening Distance, ft*
Unobstructed Intervening Buildings
Fixed -Guideway Systems
Commuter Rail Mainline
750
375
Commuter Rail Station
With Horn Blowing
1,600
1,200
Without Horn Blowing
250
200
Commuter Rail Road Crossing with Horns and Bells
1,600
1,200
RRT
700
350
RRT Station
200
100
LRT
350
175
Streetcar
200
100
Access Roads to Stations
I 00
50 Low and Intermediate
Capacity Transit
Steel Wheel
125
50 Rubber Tire
90 40
Monorail
175
70 Yards and Shops
1000
650
Parking Facilities
I 25
75 Access Roads to Parking
I 00
50 Ancillary Facilities: Ventilation Shafts
200
100
Ancillary Facilities: Power Substations
250
125
Bus Systems
Busway
500
250
Bus Rapid Transit (BRT) on exclusive roadway
200
100
Bus Facilities
Access Roads
I00
50 Transit Mall
225
150
Transit Center
225
150
Storage & Maintenance
350
225
Park & Ride Lots w/Buses
225
150
Ferry Boat Terminals
300
150
*Measured from centerline of guideway for fixed -guideway sources, from the ROW on both sides of the roadway for highway/transit sources, from the center of noise -generating activity for stationary sources, or from the outer boundary of the proposed project site for fixed facilities spread out over a large area.

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Table 4-8 Assumptions for Screening Distances for Noise Assessments Type of Project Operations Speeds* Metric**
Fixed -Guideway Systems
Commuter Rail Mainline
66 day /12 night; I loco, 6 cars
55 mph
Lan
Commuter Rail
Station
With Horn Blowing
22 day / 4 night
N/A
Lan
Without Horn Blowing
22 day / 4 night
N/A
Ldn
Commuter Rail -Highway Crossing with Horns
and Bells
22 day / 4 night
55 mph
Ldn
RRT
220 day / 24 night; 6 -car trains
50 mph
Lan
RRT Station
220 day / 24 night
20 mph
Lan
LRT
150 day / 18 night; 2 artic veh.
35 mph
Lan
Streetcar
150 day / 18 night
25 mph
Lan
Access Roads to Stations
1000 cars, 12 buses
35 mph
Leg(hr)
Low and
Intermediate
Capacity Transit
Steel Wheel
220 day / 24 night
30 mph
Lan
Rubber Tire
220 day / 24 night
30 mph
Lan
Monorail
220 day / 24 night
30 mph
Lan
Yards and Shops
20 train movements
N/A
Leq(I hr)
Parking Facilities
1000 cars
N/A
Leg(ihr)
Access Roads to Parking
1000 cars
35 mph
Legoho
Ancillary Facilities: Ventilation Shafts
Rapid Transit in Subway
50 mph
Lan
Ancillary Facilities: Power Substations
Sealed shed, air conditioned
N / A
Lan
Bus Systems
Busway
30 buses, 120 automobiles
50 mph
Leglin j
BRT on exclusive roadway
30 buses
35 mph
Legpnrj
Bus Facilities
Access Roads
1000 cars
35 mph
Leg(ihr)
Transit Mall
20 buses
N/A
Leglinr)
Transit Center
20 buses
N/A
Leg( Ihr)
Storage & Maintenance
30 buses
N/A
Leg(ihr)
Park & Ride Lots
w/Buses
1000 cars, 12 buses
N/A
�gi'hr)
Ferry Boat Terminals
8 boats with horns used in
docking cycle
N/A
Leg('hr)normal
*N/A = not applicable
**Loh-) = the loudest hour of project related activity during hours of noise sensitivity.

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4.4 Evaluate Impact: General Noise Assessment
The General Noise Assessment should be completed after the Noise Screening Procedure (Section 4.3), through which noise -sensitive receivers have been identified. This can be completed either by using the General Noise Assessment Procedure described below or using the FTA General Noise Assessment Spreadsheet found on the following FTA website:
http://www.fta.dot.gov/ 12347_2233.html.

Assumptions are used throughout the General Noise Assessment. If the listed assumptions are not appropriate for the project and good engineering judgement cannot be used by following the General Noise Assessment procedure, proceed to a Detailed Noise Analysis or consult with the FTA Regional office.

Major steps in the General Noise Assessment procedure and recommended workflow are shown in Figure 4-5 and listed below. Four examples of General Noise Assessments are given at the end of this section. Many of these concepts are explained in greater detail in the context of a Detailed Noise Analysis in Section 4.5.

Step I: Identify Noise -Sensitive Receivers — Identify noise -sensitive receivers (Section 4.3) and their proximity to the project and major noise sources.

Step 2: Determine Project Noise Source Reference Levels — Determine the project noise sources and reference levels. Then, estimate the project noise exposure at the reference distance of 50 ft considering operational characteristics with preliminary estimations of the effect of mitigation.

Step 3: Estimate Project Noise Exposure by Distance — Estimate project noise exposure at distances beyond 50 ft considering propagation characteristics using a simplified procedure.

Step 4: Combine Noise Exposure from All Sources — Combine all sources associated with the project to predict the total project noise at the receivers.

Step 5: Measure Existing Noise Exposure — Measure the existing noise or estimate the existing noise exposure using a simplified procedure.

Step 6: Inventory Impacts
Option A: Tabulate the change in noise (existing vs. estimated project noise) at each noise -sensitive receiver or cluster, identifying all moderate and severe impacts.

Option B: Take inventory of noise -sensitive receivers that fall within the moderate and severe noise contours.

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Step 7: Determine Noise Mitigation Needs — Evaluate the need for mitigation and repeat the General Noise Assessment with proposed mitigation.

Project
Sources
Operatioinal
Characteristics
Propagation
Characteristics
Figure 4-5 Procedure for General Noise Assessment
Noise Impact
Criteria
Study Area
Characteristics
Locat'on of
Noise -Sensitive
Sites
Noise rived
Inventory
Step I: Identify Noise -Sensitive Receivers
Determine the proximity of noise -sensitive land uses identified in Section 4.3 to the project and to the nearest major roadways and railroad lines.

I a. When necessary, use windshield surveys or detailed land use maps to confirm the location of noise -sensitive land uses.

Ib. For land uses more than 1,000 ft from major roadways or railroad mainlines, obtain an estimate of the population density in the immediate area, expressed in people per square mile. Distances to roadways or railroads, or population density, will be used later to estimate the existing FEDERAL TRANSIT ADMINISTRATION 38
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noise level. Coordinate with the Metropolitan Planning Organization (MPO) for population densities at an appropriate level of detail.

Step 2: Determine Project Noise Source Reference Levels Determine the general source reference /eve/ for each project noise source.

Classify all project noise sources as fixed -guideway transit, highway/transit, or stationary facility and determine the source reference levels. Note that a major fixed -guideway system will have stationary facilities associated with it and that a stationary facility may have highway/transit elements associated with it.

Option A: Fixed -guideway Transit Sources — For this manual, fixed - guideway transit sources include commuter rail, RRT, LRT, streetcar, AGT, monorail, and magnetically levitated vehicles (maglev). For commuter railroads and LRT systems, the crossing of streets and highways at -grade is likely, and in that case, warning devices should be included in the assessment. At an early project stage, the information available for a General Noise Assessment includes:
• Candidate transit mode
• Guideway options
• Time of operation
• Operational headways
• Design speed
• Alternative alignments
This information is not sufficient to predict noise levels at all locations along the ROW. Therefore, use conservative estimates (e.g., maximum (expected) design speeds and operations at design capacities) to estimate worst -case noise levels.

First choose the appropriate fixed -guideway transit source reference level and then predict the noise exposure at 50 ft in terms of Legonoand Ldn.

A.i. Choose the reference source noise levels 50 ft from the track for one vehicle in terms of Sound Exposure Level (SEL) using Table 4-9. See Appendix B for a detailed explanation of SEL. Note that the SEL reference speed is 50 mph, unless otherwise noted.

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Table 4-9 Reference SEL's 50 ft from Track and at 50 mph, One Vehicle Source
Type
Reference Conditions
Reference
SEL (SELref),
dBA
Commuter
Rail, At -Grade
Locomotives
Diesel-electric, 3000 hp, throttle 5
92 Electric
90 Diesel Multiple Unit (DMU)
Diesel -powered, 1200 hp
85 Horns
Within '/< mile of grade crossing
110
Cars
Ballast, welded rail
82 Rail Transit and Streetcars at 50 mph
At -grade, ballast, welded rail
82 Rail Transit and Streetcars at 25 mph
At -grade, ballast, welded rail
76 Transit whistles / warning devices
Within 1/8 mile of grade crossing
93 AGT
Steel Wheel
L Aerial, concrete, welded rail
80 Rubber Tire
Aerial, concrete guideway
78 Monorail
Aerial straddle beam
82 Maglev
Aerial, open guideway
72 A.ii. Collect the following data:
• Number of train passbys during the day (7 a.m. to 10 p.m.) and night (10 p.m. to 7 a.m.) for category 2 land uses
• Maximum number of train passbys during hours that category 1 or category 3 land uses are normally in use (typically the peak hour train volume)
• Number of vehicles per train for each time period for category 2 land uses (if this number varies during the day or night, take the average) • Maximum number of vehicles per train during hours that category I or category 3 land uses are normally in use (typically the peak hour train volume)
• Train speed in mph (maximum expected)
• Guideway configuration
• Location of highway and street grade crossings, if any • If this process is repeated to estimate the effect of proposed noise mitigation, include the noise barrier location
A.iii. Calculate the noise exposure at 50 ft in terms of Lego no:
• Calculate Leq(Ihr) for each source using the appropriate equations in Table 4-10.
• Compute Leq(Ihr).conbo using Eq. 4-6. It may be necessary to compute the combined totals with and without warning horns. Some neighborhoods along the corridor may be exposed to horn noise, but some may not.

A.iv. Calculate the noise exposure at 50 ft in terms of Ld,,:

If the project noise will affect any residential receivers, calculate the Ld„ using the combined Lego hr)for both the daytime and nighttime periods separately, using the appropriate equations in Table 4-10.

It may be necessary to calculate Ld„ with and without warning horns, as in the previous step.

Note that the equations in Table 4-10 include terms to account for a difference in speed from the 50 mph reference speed and a numerical adjustment to account for the one -hour time period for this metric. For FEDERAL TRANSIT ADMINISTRATION 40
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more information on the numerical adjustment to represent the time period of interest, see Appendix 8.1.4.4.

Table 4-10 presents an estimate of the noise reduction potentially provided by wayside noise barriers that can be used when assessing mitigation options in a General Noise Assessment. If impact is determined during the General Noise Assessment, repeat the procedure and include proposed mitigation according to Section 4.4, Step 7. See Section 4.5, Step 7 for a complete description of the benefits resulting from various noise mitigation measures that can be evaluated with a Detailed Noise Analysis.
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Table 4-10 Computation of Noise Exposure at 50 ft for Fixed -Guideway General Noise Assessment Locomotives*
Leq(Ih )at 50 ft
5 Leq.Loco(1hr) = SEELref + 101og(NLoco) + Klog ( )) + lO log(V) — 35.6 Eq. 4-I Locomotive
Warning
Horns**
Leq(i hr)at 50 ft
= o
L eq.LHorns(lhr) SEL ref + 10 log ) — 35.6 Eq. 4-2
Rail Vehicles?
L I(Ih.)at 50 ft
S
Leq.Rcars(1hr) = SELref + 101og(Ncars) + 201og(50) + 10 log (V) — 35.6 +Adjtrack Eq. 4-3 Streetcars
(25lo mph or
slower)
Lropnr) at 50 ft
L SEL + 1010 N ) + 210 S + 10 to V 35.6 + Ad
egscars(1hr) = ref g( cars g(25) log(V)— — )track Eq. 4-4 Transit
Warning Horns
l.,(ih)at 50 ft
S
Leq,rttorns(1hr) = SELref —10 log(50) + 10 log(V) — 35.6 Eq. 4-5 Combined
Locomotive and
transittf
L¢q(Ihr) at 50 ft
Leq.Loco(ihr) Leq.RCars(ihr) Leq.SCars(ihr)
Leq.comho hr) = 101000' '10', + 10( X10) + 10( /10)
(1
L.eq.LHarns(1h ) Leq.THorns(1hr) Eq. 4-6
+ 10( X10) + 10( X10)
Daytime
La at 50 ft
L L where V = Vd, NLoco = Na loco events), and Ncars = Na(car events d = eq(1hr) ( Eq. 4-7
Nighttimef L
La at 50 ft
L where V = Vn, NL,c, = Na loco events), and Ncar: = Na(car events) n = eq(lhr) ( % Eq.4-8
La', atl O1ftht
Lan = 10Iog(15 x 10(La4o) + 9 x 10((Ln+1°)h10)) - 13.8 Eq. 4-9 NLoco = average number of locomotives per train
K = constant
-I0 for passenger diesel
0 for DMUs
+10 for electric
S = train speed, mph
V = average hourly volume of train traffic, trains per hour Ncars = average number of cars per train
Adjtrack = constant
+5 for jointed track or for a crossover within 300 ft
+4 for aerial structure with slab track (except AGT and monorail) +3 for embedded track on grade
-5 if a noise barrier blocks the line of sight
Vd = average hourly daytime volume of train traffic, V„ = average hourly nighttime volume of train traffic, trains per hour trains per hour
number of trains, 7 a. m. to 10 p. m. number o f trains, l0 p. m. to 7a. m. _
15 9
Nd = average hourly number of events that occur N, = average hourly number of events that occur during during daytime (7 a.m. to I 0 p.m.) nighttime (10 p.m. to 7 a.m.) number of events between 7 a.m. to 10 p. m. number o f events between 10 p. m. to 7 a. m. 15 9
* Assumes a diesel locomotive power rating at approximately 3000 hp. **Based on FRA's horn noise model ( http://www.fra.dot.gov/eLib/Details/L0409I) . t Includes all commuter rail cars, transit cars, streetcars above 25 mph, AGT and monorail. t t Only include appropriate terms.

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Option B: Highway/Transit Sources — The highway/transit type sources include most transit modes that do not require a fixed -guideway. Examples are high -occupancy vehicles, such as buses, commuter vanpools and carpools. Use the instructions below to estimate source noise levels for projects that involve these types of vehicles and are using FTA's environmental review procedures.

At an early project stage, the information available for a General Noise Assessment includes:
• Vehicle type
• Transitway design options
• Time of operation
• Typical headways
• Design speed
• Alternative alignments
This information is not sufficient to predict noise levels at all locations along the ROW; therefore, use of conservative estimates (e.g., maximum (expected) design speeds and operations at design capacities) to estimate worst -case noise impact levels is recommended. The procedure is consistent with FHWA's highway noise prediction method. The reference SEL levels in Table 4-11 correspond to FHWA's source emission levels and speed coefficients for buses and automobilesJ22)
B.i. Using Table 4- I 1, choose the appropriate reference source noise levels 50 ft from the roadway in terms of SEL. Note that the SEL reference speed is 50 mph, unless otherwise noted.

Table 4-11 Source Reference Levels at 50 ft from Roadway, 50 mph Source* Reference SEL, dBA
Automobiles and Vans
74 Buses (diesel -powered)
82 Buses (electric)
80 Buses (hybrid)
83**
Assumes normal roadway surface conditions.

For hybrid buses, determine Reference SEL on a
case -by -case basis because they vary, and data are
scarce.

B.ii. Collect the following data:
• Number of vehicle passbys during the day (7 a.m. to 10 p.m.) and night (10 p.m. to 7 a.m.) for each vehicle type in Table 4 -I I, if a category 2 land use is present
• Number of vehicle passbys during hours that category I or category 3 land uses are normally in use, each vehicle type in Table 4- I 1 • Speed (maximum expected)
• Transitway configuration (with or without noise barrier) B.iii. Calculate the noise exposure at 50 ft in terms of Leq(Ihr). Calculate Leq(Ihr) for each source using the appropriate equations in Table 4-12.

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B.iv. Calculate the noise exposure at 50 ft in terms of Ldp. If the project noise will affect any residential receivers, calculate the Ldn using the combined Leq(Ihr) for both the daytime and nighttime periods separately, using the appropriate equations in Table 4-12.

Note that the equations in Table 4-12 include terms to account for a speed other than the 50 mph reference speed and a numerical adjustment to account for the one -hour time period for this metric. For more information on the numerical adjustment to represent the time period of interest, see Appendix B.I.4.4.

Table 4-12 presents an estimate of noise reduction potentially provided by wayside noise barriers. This is considered illustrative given that barriers are the most common noise mitigation measure. See Section 4.5, Step 7 for a complete description of the benefits resulting from noise mitigation. If impact is determined during the General Noise Assessment without mitigation, repeat the procedure and include proposed mitigation.

Table 4-I2 Computation of Leq(ihr) and Ld„ at 50 ft for Highway/Transit General Noise Assessment Leq(Ihr) at 50 ft
Leq(lhr) = SELre f + 10 log(V) + Cslog(50) — 35.6
Eq. 4-10
Daytime
La at 50 ft

Ld = Laeq( 1hr) where V = Va
Eq. 4-1
Nighttime
L„ at 50 ft
Ln = Laeq(lhr) where V = V,
Eq. 4-12
Lam at 50 ft
Ldn = 101og(15 x 10(Ld�lo) + 9 x 10((Ln+lo)/lo)) — 13.8 Eq. 4-13
Barrier
Adjustment
= -5 for noise barriers
V
Cs
S
Vd
V„
= hourly volume of vehicles, vehicles per hour
= Speed constant
15 for diesel buses
28 for electric buses
21 for hybrid buses(23)
30 for automobile and van pools
= average vehicle speed, mph
= average hourly daytime volume of vehicles, vehicles per hour total number o f vehicles, 7 a. m. to 10 p.m.
15 = average hourly nighttime volume of vehicles, vehicles per hour total number of vehicles, 10 p. m. to 7 a.m.
9 Option C: Stationary Sources — Stationary sources include fixed transit system facilities. New transit facilities undergo a site review for best location that considers the noise sensitivity of surrounding land uses. Although many facilities such as bus maintenance garages are usually located in industrial and commercial areas, some facilities such as bus terminals, ferry terminals, train stations, and park -and -ride lots may be placed near residential neighborhoods where noise impact may occur. Access roads to some of these facilities may also FEDERAL TRANSIT ADMINISTRATION 44
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pass through noise -sensitive areas. Noise from access roads is treated according to the procedures described in the Highway/Transit Sources category. In a General Noise Assessment, only the prominent features of each fixed facility are considered in the noise analysis.

C.i. For small facilities, using Table 4-13, determine the reference source noise levels 50 ft from the center of the site in terms of SEL. The source reference levels given in the table are based on measurements for the peak hour of operation of a typical stationary source of the noted type and size.

A large facility, such as a rail yard, is spread out over considerable area with various noise sources with different noise levels depending on the layout of the facility. Specifying a single reference SEL for the facility at 50 ft from the center of the site could be misleading if all of these different noise sources are not represented. Therefore, the reference distance should be the equivalent distance of 50 ft, which is determined by estimating the noise levels from the center of the site at a distance far enough to capture all noise sources and projecting back to 50 ft from the center of the site. This approach allows for a conservative estimate of noise for all surrounding areas and the equivalent noise can be considered as concentrated at the center of the site. If the location of noise sources is known, then the distance should be taken from the point of the noisiest activity on the site (e.g., the dock in the case of ferry boat operations) instead of the center of the site.

Table 4-I3 Source Reference Levels at 50 ft from Center of Site, Stationary Sources Source
Reference
SEL, dBA
Reference Conditions
Rail System
Yards and shops
118
20 train movements in peak activity hour
Layover tracks (commuter rail)
109
I train with diesel locomotive idling for I hour
Crossing signals
109
3600 second duration
Bus System
Storage yard
I I I
100 buses accessing facility in peak activity hour
Operating facility
114
100 buses accessing facility, 30 buses serviced and
cleaned in peak activity hour
Transit center
101
20 buses in peak activity hour
Ferry Terminal
Ferry boat (no fog horn sounded)
97 4 ferry boat landings in I hour
Ferry boat (fog horn sounded)
100
Parking Garage
92 1000 -car capacity in peak activity hour
Park & Ride Lot
101
12 buses, 1000 cars in peak activity hour
C.ii. Collect the following data:
• Number of layover tracks and hours of use
■ Number of buses, if different from assumed reference conditions (if this number varies during the day or night, take the average) • Number of ferry boat landings, if different from assumed reference conditions (if this number varies during the day or night, take the average)
• Actual capacity of parking garage or lot
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C.iii. Calculate Leg('hr) at 50 ft. Calculate Leg('hr) for each source using the appropriate equations in Table 4-14.

C.iv. Calculate Ldr, at 50 ft. If the project noise will affect any residential receivers, calculate the Ldn using the combined Lego hr)for both the daytime and nighttime periods separately, using the appropriate equations in Table 4-14.

The equations in Table 4-14 include a numerical adjustment to account for the one -hour time period for this metric. See Appendix B.1.4.4 for more information on the numerical adjustment.

Table 4-14 presents an estimate of noise reduction potentially provided by noise barriers at the property line. Only approximate locations and lengths for barrier or other noise mitigation measures are developed during a General Noise Assessment to provide a preliminary indication of the costs and benefits of mitigation. A Detailed Noise Analysis of the preferred alternative is usually warranted following the General Noise Assessment (if it predicts any impacts) to verify impacts and design the mitigation.
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Table 4-14 Computation of Leg('hr) and Lm, at 50 ft for Stationary Source General Noise Assessment* Leg(' hr) at 50 ft
LegClhr) = SELYej + CN — 35.6 Eq. 4-14
Daytime
Ldat50ft
1 LAeq(1hr)/ )
Ld=101og((1) 10( 10) Eq. 4-15
lam-10pm
Nighttime
L at 50 ft
1 (L"eq«" >/ )
L = 101og((9) 10 10 ) Eq. 4-16
l Opm-lam
Ldp at 50 ft
Ldn = 10log(15 x 10(La/10) + 9 x 10((L„+10)/10)) - 13.8 Eq. 4-17 Barrier
Adjustment
= -5 for noise barrier at property line
Volume
Adjustment
= CN
= 101og(4) Rail yards and shops
= 10log(NT) Layover tracks
= 101og(00) Bus storage yard
= 101og( oo + Oo) Bus operating facility
= 101og(ZB) Bus transit center
= 101og(4) Ferry terminal
= 101og(a) Parking garage
NA NB Park & ride lot
= 101og(2000 + za)
= lolog(s o0) Crossing signals
NT = average number of trains per hour during the day (7AM to I 0PM) or night (10PM to 7AM)
NB = average number of buses per hour during the day or night NF = average number of ferry boat landings per hour during the day or night Ns. = average number of buses serviced and cleaned per hour during the day or night NA = average number of automobiles per hour during the day or night E = average hourly duration of events, sec during the day or night * If any of these numbers is zero, omit that term.

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Step 3: Estimate Project Noise Exposure by Distance
Estimate the project noise exposure for locations beyond the reference distance, such as for noise -sensitive land uses.

In the previous step, noise exposure at the reference distance of 50 ft was calculated for the various noise sources. This step describes how to estimate the project noise exposure beyond (or, if needed, closer than) the reference distance, such as at noise -sensitive land uses locations. This procedure estimates the source's noise exposure as a function of distance. Adjustments are provided to account for shielding attenuation from rows of buildings. 3a. Select the appropriate distance correction curve (Fixed -Guideway & Highway or Stationary) from Figure 4-6. The Fixed -Guideway & Highway curve refers to line sources while the Stationary curve is refers to point sources. The distance correction factor (Cd;.ance) is 0 dB at 50 ft. 3b. Choose a distance other than 50 ft, such as the distance to a receiver.

Determine the correction factor using Figure 4-6 or calculate using the equations in Table 4- 15.00 For distances beyond 1,000 ft, the equations in Table 4-15 can be used; however, ground effects have an upper limit and atmospheric conditions may affect propagation characteristics. More detailed calculation methods may be required to account for those effects beyond I ,000 ft. 01-31
m
v -20
`o
V
-30
C
-40
50 Stationary
Fixed -guideway & Highway
10 20
30 -40
60 80 100 150 200 250 300 400 500 600 800 1000
Distance, ft
Figure 4-6 Curves for Estimating Exposure vs. Distance in General Noise Assessment Note that the curves and equations assume acoustically soft ground beyond a distance of 50 ft. See Table 4-27 for more detailed calculation of ground attenuation.

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Table 4-I 5 Distance Correction Factor Equations for General Noise Assessment Source
Equation
Stationary Sources
Cdistance = _251og(5)
Eq. 4- I8
Fixed -guideway and Highway
D
Cdistance =—151og(0)
Eq. 4-I9
D = distance, ft
3c. Apply the distance correction (Cdistance) to the project noise exposure at 50 ft (Section 4.4, Step 2) using the following equation:

Cdistance = L50 + Cdistance
where:

Ldistance = kin or Leq(lhr) at the new distance in feet L50 = Ldn or Leq(lhr) at 50 ft
Eq. 4-20
3d. Repeat Step 3c for each source -receiver distance from the project. A noise exposure vs. distance curve can be created, if desired, by calculating the noise exposure for all distances of interest and plotting a curve. This curve can be used to assist in determining the noise impact contour for the first row of unobstructed buildings. This plot can be used to display noise from both unmitigated and mitigated conditions to assess the potential benefits from mitigation measures.

For second row receivers and beyond, it is necessary to account for shielding attenuation from rows of intervening buildings. Without accounting for shielding, impacts may be substantially overestimated. Use the following general rules to account for the effect of shielding from intervening rows of buildings:
■ Assign 4.5 dB of shielding attenuation for the first row of intervening buildings only.
• Assign 1.5 dB of shielding attenuation for each subsequent row, up to a maximum total attenuation of I O dB.

Step 4: Combine Noise Exposure from All Sources
Combine all sources to predict the total project noise at the receivers using the equations in Table 4-16, once propagation adjustments have been made for the noise exposure from each source separately (fixed -guideway, highway/transit, and stationary).

Table 4-I6 Computing Total Noise Exposure
Total Leggy from all sources
for the hour of interest:

Leq.total(lhr) = g(�aLlsources 1010 10Leq/10)
Eq. 4-21
Total L. from all sources
Ldn. total = 10log(Eall sources 10Ldn/10)
Eq. 4-22
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Step 5: Estimate Existing Noise Exposure
Measure the existing noise or estimate the existing noise exposure using a simplified procedure.

Existing noise in the project vicinity must be quantified and compared to the project noise to determine the potential noise impact. It is generally recommended to measure existing noise, especially at locations known to be noise -sensitive, but if measurement results are not available then they must be estimated. In the Detailed Noise Analysis, the existing noise exposure is usually based on noise measurements at representative locations in the community.

It is not necessary or recommended that
existing noise exposure be determined by
measuring at every noise -sensitive
location in the project area. Rather, the
recommended approach is to
characterize the noise environment for
"clusters" of sites based on measurements
or estimates at representative locations in
the community. Because of the sensitivity
of the noise criteria to the existing noise
exposure, careful characterization of pre -
project ambient noise is important.

Guidelines for selecting representative
receiver locations and determining
ambient noise are provided in Appendix D and Appendix E, respectively.

Changes to Existing Transit
For projects that propose
changes to an existing transit
system, such as a rehabilitation
project, the project noise can
include changes to the existing
noise because of the project,
and so it is not possible to
define project noise separately.

For these projects, refer to
Section 4.1, Step 3 — Option B,
on using the cumulative
noise criteria.

This section describes how to estimate the existing noise in the project study area from general data available early in project planning. The procedure uses Table 4-17, where a neighborhood's existing noise exposure is based on proximity to nearby major roadways or railroads, or on population density. For areas near major airports, published aircraft noise contours can also be used to estimate the existing noise exposure. The process is as follows:
5a. Obtain scaled mapping and aerial photographs showing the project location and alternatives. A scale of I inch = 200 or 400 ft is convenient for the accuracy needed in the noise assessment. The size of the base map should be sufficient to show distances of at least 1000 ft from the center of the alignment or property center, depending on whether the project is a line source (fixed guideway/ roadway) or a stationary facility. These data are commonly available from local transit agencies and a number of publicly available online tools. 5b. Estimate the existing noise exposure by estimating the noise from major roads and railroad lines or by population density. First, evaluate the site's proximity to major roads and railroad lines including those that are included in the project. If these noise sources are far enough away that ambient noise is dominated by local streets and community activities, estimate the existing noise based on population density. To choose the appropriate existing noise exposure, compare noise levels from each of the three categories —Roadways, Railroads, and Population Density —and select the lowest level. In case of a FEDERAL TRANSIT ADMINISTRATION 50
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lightly used railroad (one train per day or less) select the Population Density category. Existing noise levels are presented in Table 4-17. Refer to Section 4.1, Step 3 — Option B, on using the cumulative noise criteria for projects that propose changes to an existing transit system, such as a rehabilitation project.

Option A: Roadways — Major roadways are separated into two categories for a general noise assessment. Roadways that cannot be described by these two categories are not considered major roadways and would use the Population Density method described below. The roadway categories are as follows:
• Interstate highway —roadways with 4 or more lanes that allow trucks • Other roadway —parkways without trucks and city streets with the equivalent of 75 or more heavy trucks per hour or 300 or more medium trucks per hour
The estimated roadway noise levels in Table 4-17 are based on data for light to moderate traffic on typical highways and parkways using FHWA highway noise prediction procedures. Where a range of distances is given, the noise exposure estimates are given at the larger distance (note that the traffic noise at the smaller distance is underestimated). For highway noise, distances are measured from the centerline of the near lane for roadways with two lanes, while for roadways with more than two lanes the distance is measured from the geometric mean of the roadway. This distance is computed as follows:

DGM = V (DN)(DF)
where:

DGM = distance to the geometric mean in feet
DN = distance to the nearest lane centerline in feet
DF = distance to the farthest lane centerline in feet
Eq. 4-23
Option B: Railroad Lines — For railroads, the estimated noise levels are based on an average train traffic volume of 5-10 trains per day at 30-40 mph for main line railroad corridors and the noise levels are provided in terms of Ld„ only. Distances are referenced to the track centerline, or in the case of multiple tracks, to the centerline of the rail corridor. Because of the intermittent nature of train operations, train noise will affect the Lego hr) only during certain hours of the day, and these hours may vary from day to day. Therefore, to avoid underestimating noise impact when using Leq(Ihr) , it is recommended that sites near rail lines are estimated based on nearby roadways or population density unless very specific train information is available.

Option C: Population Density — In areas away from major roadways, noise from local streets or in neighborhoods is estimated using a relationship determined during a research program by EPA.(24) EPA determined that ambient noise can be related to population density in locations away from transportation corridors, such as airports, major roads and railroad tracks, according to the following relation:

Lan = 22 + 101og(p)
Eq. 4-24
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where:

Lan = in dBA
p = population density in people per square mile
In areas near major airports, published noise contours can be used to estimate the existing noise exposure. The Ldn from such contours should be applied if greater than the estimates of existing noise from other sources at a given location.

Table 4-17 Estimating Existing Noise Exposure for General Noise Assessment Dominant
Existing Noise
Source
D'Noise Sfource ft*or
Population
Density, people
per sq. mi.

Noise Exposure Estimates
Leq
Day
Leg
Evening
Leq
Night
L dp
10-50
75 70
65 75
50-100
70 65
60 70
Interstate
100-200
65 60
55 65
Highway**
200-400
60 55
50 60
400-800
55 50
45 55
800 and up
50 45
40 50
10-50
70 65
60 70
50-100
65 60
55 65
Other Roadwayt
100-200
60 55
50 60
200-400
55 50
45 55
400 and u
50 45
40 50
10-30
--
--
--
75 30-60
--
--
--
70 60-120
--
--
--
65 Railwaytt
120-240
--
--
--
60 240-500
--
--
--
55 500-800
--
--
--
50 800 and up
--
--
--
45 1-100
35 30
25 35
100-300
40 35
30 40
300-1000
45 40
35 45
Population
1000-3000
50 45
40 50
3000-10000
55 50
45 55
10000-30000
60 55
50 60
30000 and up
65 60
55 65
* Distances do not include shielding from intervening rows of buildings. Generally, for estimating shielding attenuation in populated areas, assume I row of buildings every 100 ft, 4.5 dB for the first row, and 1.5 dB for every subsequent row up to a maximum of 10 dB attenuation. ** Roadways with 4 or more lanes that permit trucks, with traffic at 60 mph. j• Parkways with traffic at 55 mph, but without trucks, and city streets with the equivalent of 75 or more heavy trucks per hour and 300 or more medium trucks per hour at 30 mph. ft Main line railroad corridors typically carrying 5-10 trains per day at speeds of 30-40 mph.

Step 6: Inventory Noise Impacts
Inventory the potential noise impacts either by comparing the project and existing noise at each noise -sensitive land use or by developing noise impact contours.

Use land use information and assumptions for shielding attenuation from rows of buildings. In some cases, it may be necessary to supplement the land use information or determine the number of dwelling units within a multi -family building with a visual survey. If the objective is to compare major alignment options, it may not be necessary to identify every different type of noise - FEDERAL TRANSIT ADMINISTRATION 52
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sensitive land use. The inventory may include a subset of land uses, including residential and public institutional uses.

Option A is the preferred method as it quantifies the noise impact at each noise -sensitive land use indicating the severity of the impact. Option B may be useful for comparing and narrowing down major alignment options with numerous noise -sensitive land uses.

Option A: Compare existing noise to project noise at each noise - sensitive land use.

AI. Tabulate each individual noise -sensitive land use building and site within the identified screening distance (Section 4.3).

A2. Determine for each noise -sensitive land use the existing noise (Section 4.4, Step 5), the project noise (Section 4.4, Step 3) and the resulting change in noise.

A3. Designate each noise -sensitive land use with either a no, moderate, or severe noise impact based on the criteria in Section 4.1.

A4. Identify all moderate and severe impacts on a project map.

Option B: Develop noise impact contours.

B I . Determine the noise level thresholds at which the project noise would cause moderate and severe impacts using the estimated existing noise exposure from Section 4.4, Step 5 and the noise impact criteria in Figure 4-2.

B2. Determine the distances from the project boundary to the two impact levels using the noise exposure vs. distance curves or equations in Section 4.4, Step 3.

B3. Plot points on a project land use map that correspond to the distances determined in Section 4.4, Step 3. Continue this process for all areas surrounding the project. Connect the plotted points to represent the noise impact contours.

B4. Tabulate all noise -sensitive land use buildings and sites that lie between the impact contours and the project boundary. For residential buildings, an estimate of the number of dwelling units is satisfactory.

B5. Prepare summary tables showing the number of buildings (and estimated dwelling units, if available) within both impact categories.

Specific decibel level noise contours, for example, 65 dBA, can also be plotted if desired. The distances can be determined using the procedure in Section 4.4, Step 3 by substituting the desired decibel level for the impact threshold.

Locations of points will change with respect to the project boundary as the existing ambient exposure changes, the project source levels change, and as shielding effects change. It is recommended to plot points close together to FEDERAL TRANSIT ADMINISTRATION 53
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draw a smooth curve. For a General Noise Assessment, the contours may be drawn through buildings and terrain features as if they were not present. This practice is acceptable considering the level of detail associated with a project in its early stages of development. Example 4- I and Example 4-4 describe the development of noise contours with illustrations.

Step 7: Determine Noise Mitigation Needs
Apply estimates of the noise reduction from proposed mitigation measures (Section

4.4, Step 2), where the assessment shows either severe or moderate impact, and repeat the tabulation of noise impacts.

Note that noise barriers are the only form of mitigation available in a General Noise Assessment. The other mitigation measures are available for a Detailed Noise Analysis. The approximate noise barrier lengths and locations developed in a General Noise Assessment provide a preliminary basis for evaluating the costs and benefits of impact mitigation. This evaluation will provide a conservative estimate of the effect of the mitigation on the identified impacts.

In general, it is recommended to complete a Detailed Noise Analysis for final mitigation measures. However, if impact is identified through a General Noise Assessment and can be mitigated to a level of no impact using the noise reduction estimates included in the General Noise Assessment, a Detailed Noise Analysis may not be needed. Mitigation assumed in the assessment used for the NEPA evaluation must be included in the project as a commitment.

Consult with the FTA Regional office to determine if a Detailed Noise Analysis is required for final mitigation measures.

The following examples illustrate how to complete general noise assessments for varying project types including commuter rail, highway/transit, BRT system, and a transit center.

Example 4-I General Noise Assessment — Commuter Rail
General Noise Assessment for a Commuter Rail System in an Existing Abandoned Railroad Right -of -Way
The following example illustrates the General Noise Assessment procedure for a new fixed -guideway project.

The hypothetical project is a commuter rail system to be built within the abandoned ROW of a railroad. The example covers a segment of the corridor that passes through a densely developed area with population density of 25,000 people per square mile in mixed single- and multi -family residential land uses as shown in Figure 4-7.

The example is presented in two parts: first, a segment where the rail line is grade -separated and a horn is not sounded; and second, an at -grade street -rail crossing where the horn is sounded.

Assumptions
• Project Corridor
Existing population density is 25,000 people per square mile. • Commuter Rail System
Commuter train with one locomotive and a three -car consist on a double -track at -grade system with welded rail. Trains operate with 20 -minute headways during peak hours and I -hour headways during off-peak. Speeds are approximately 40 mph along the corridor.

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Operating Schedule
Period
Headway
Inbound
(minutes)
Outbound
Trains
Inbound
per hour
Outbound Total
Period
Total
7 a.m. - 8 a.m.
20 20
3 3
6 6
Daytime
8 a.m. - 4 p.m.
60 60
I
I
2 16
4 p.m. - 6 p.m.
20 20
3 3
6 12
6 p.m. - 10 p.m.
60 60
I
1 2
8 10 p.m. - l 1 p.m.
60 60
I
I
2 2
Nighttime
11 p.m. - 5 a.m.
--
--
--
--
--
--
5 a.m. - 6 a.m.
60 60
I
I
2 2
6 a.m. - 7 a.m.
20 20
I
I
2 2
Part I: Grade -Separated Street Crossing
Determine Project Source Reference Levels at 50 ft
Classify the noise source: Fixed -Guideway Transit
Determine noise source reference level from Table 4-9:

Locomotive: 92 dBA
Cars: 82 dBA
Estimate Project Noise Exposure at 50 ft
Determine average hourly daytime and nighttime volumes of train traffic.

Daytime (7 a.m. - 10 p.m.)
42 trains
Vd = — 2.8 trains/hour
15 hours
Nighttime (10 p.m. - 7 a.m.)
6 trains
V = — 0.7 trains/hour
9 hours
Use Eq. 4-I and Eq. 4-3 to calculate the daytime Leg(ihr) at 50 ft for the locomotives and rail cars.

S
Ld.Locos = SELref + 101og(NLocos) + Klog(50) + 101og(Vd) — 35.6 40 = 92 + 10log(1) — 101og(50) + 10log(2.8) — 35.6
=61.8dBAat50ft
S
Ld.RCars = SELref + 101og(Ncars) + 201og(0) + 10log(Vd) — 35.6 40 = 82 + 10log(3) + 201og(50) + 101og(2.8) — 35.6
= 53.7 dB A at 50 ft
Calculate the total daytime La for the locomotive and rail cars using Eq. 4-7. = 10109(10Ld.Loca/10 + 10Ld.ftCars/10)
Ld.Combo
= 10log (1061.8/10+ 10533/10)
= 62.4 dBA at 50 ft
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Calculate the nighttime Leg( Ihr) at 50 ft for the locomotives and rail cars.

S
= SELre f + 10log(NLocos) + K log(50) + 101og(Vn) — 35.6 40 = 92 + 10 log(1) — 10log( 50) + 10 log(0.7) — 35.6
=55.8dBA at50ft
S
Ln.Rcars = SELTef + 10log(Ncars) + 20log( 50) + 101og(Vn) — 35.6 40 = 82 + 10 log(3) + 20log( 50) + 10 log(0.7) — 35.6
= 47.7 dBA at 50 ft
Calculate the total nighttime L for the locomotive and rail cars using Eq. 4-8.

Ln.Combo
= 101og(10".ro`os/io + 10L".acorVio)
= 101og(10558/10 + 10477/1a)
= 56.4 dBA at 50 ft
Calculate Ld, at 50 ft for the project using Eq. 4-9.

Ldn.combo = lolog (15 x 10(Ld.Combo/10) + 9 x 10(<L°.combo+18)/10)) — 13.8 Estimate Existing Noise Exposure
Estimate existing noise at noise -sensitive sites. Since the existing alignment is on an abandoned railroad, the dominant existing noise source can be described by a generalized noise level to characterize a large area.

Use Table 4-17 and population density of 25,000 people per square mile to determine the existing noise level. Unobstructed residences range from 100 to 200 ft from the rail line.

According to Table 4-17: L. = 60 dBA
Determine Noise Level and Distance for the Onset Of Impact Determine the noise level for the onset of moderate and severe impact using Figure 4-2 and the existing noise level of 60 dBA. Note that this project is land use category 2 and the appropriate metric is Ldn.

Existing
Noise
Lao
Onset of Moderate
Impact
Lan
Onset of Severe Impact
Lan
60 dBA
58 dBA
64 Dba
Determine the distance from the project noise sources to the noise impact contours using the fixed - guideway curve in Figure 4-6 (or the equations in Table 4-15) and the project impact thresholds obtained above. The project noise level at 50 ft is approximately 64 dBA.

Moderate impact (58 dBA)
58-64= —6 dB
According to Figure 4-6, the distance correction is approximately -6 dB at 120 ft.

Severe Impact (64 dBA)
64 — 64 = 0 dB
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According to Figure 4-6, the distance correction is less than 0 dB at approximately 51 ft.

Project Level
Ld.

Onset of Moderate
Impact
Distance
Onset of Severe
Impact
Distance
64 dBA
120 ft
51 ft
Develop Noise Impact Contours
Draw contours for each affected land use, based on the above table and its distance from the rail line (Figure 4-7). Note that the impact distances listed are in terms of distance to the centerline of the Commuter Rail corridor.

Inventory of Noise Impact
There are six residential buildings within the contours defining moderate impact (shaded in Figure 4-7).

Noise Mitigation
The procedure is repeated assuming a noise barrier to be placed at the railroad ROW line. The barrier serves to reduce project noise from the commuter rail by at least 5 dB. Note that the barrier does not affect the project criteria to be used in determining impact, and the same existing noise levels (as the case without a barrier) are used to determine these thresholds.

In this example, the noise barrier decreases the distance to moderate impact from 120 to 60 ft and eliminates all residential noise impact for this segment of the project area.

Th-QondE
ULE
Dry
Clan PEEriC a
LIED
don
120'
120
Proposed Commuter paIF
Severe Impel
[Aerate Impact
0� a ��❑ a��
--QQQ D C D R D
Figure 4-7 Noise Impacts of Hypothetical Commuter Rail
Part 2: At -Grade Crossing with Horn Blowing
Now consider the case of an active street crossing of the commuter railroad tracks. The General Noise Assessment method includes source reference levels for horns on moving trains and warning bells (crossing signals) at the street crossing. According to Table 4-9, the horn noise applies to track segments within '/< mile of the grade crossing.

Estimate Project Noise Exposure at 50 ft
Using the train volumes from Part I and the information in Table 4-9 and Table 4-10, determine the day and nighttime Leg('hr) from sounding the horns at 50 ft.

Ld.LHorns
= SEL,ef + 10 log(Vd) — 35.6
= 110 + 10 log(2.8) — 35.6
= 78.9 dBA
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Ln.LHorns
= SELYef + 101og(Vn) — 35.6
= 110 + 10 log(0.7) — 35.6
= 72.9 dBA
Calculate the Ldp at 50 ft from train horns using Eq. 4-9 :

Ldn.LHorns
= 101og(15 x 10(LdLHorns�10) + 9 x 10(<Ln.LHens+lo)/10)) 13.8 = 81 dBA
At -grade street crossings will have warning bells, typically sounding for 20 seconds for every train passby.

The total daytime and nighttime durations are as follows:

Ed
En
From Table 4-14:
= average daytime hourly duration
=20 seconds X 2.8 trains/hour = 56 seconds/hour
= average nighttime hourly duration
=20 seconds X 0.7 trains/hour = 14 seconds/hour
Ldw"" = SELref + 101og(3Ed
600) - 35.6
56 = 109 + 10 log(3600) — 35.6
= 55.3 dBA
Ln.WBell
En
= SELref + 10log( — 35.6
14 = 109 + 10log( — 35.6
= 49.3 dBA
Calculate Ldp at 50 ft. from the warning bells using Eq. 4-17:

Ldn.WBell
= 10log(15 x 10(LdWBef/io) + 9 x 10(<Ln.wBeu+1°3/10))- 13.8 = 57.3 dBA
Compared to horn blowing, the crossing signal warning bell noise is negligible, but still must be included in the evaluation.

Estimate Existing Noise Exposure
From Part I, the existing noise level is 60 dBA.

Determine Noise Level and Distance for the Onset Of Impact As in Part I, the existing noise level (60 dBA) is used to determine the onset of moderate and severe impacts:

Existing
Noise
Ldn
Onset of Moderate
Impact
Ldn
Onset of Severe Impact
Ldn
60 dBA
58 dBA
64 dBA
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Determine the distance from the project noise sources to the impact contours using the fixed -guideway curve in Figure 4-6 (or the equations in Table 4-15) and the project impact thresholds obtained above. The project noise at 50 ft is approximately 81 dBA. However, there are at least two intervening rows of buildings, which will provide 6 dB (4.5 dB for the first row and 1.5 dB for the second row) of shielding.

Moderate impact (58 dBA)
58—(81-6)= —17 dB
According to Figure 4-6, the distance correction is approximately -17 dB at 715 ft.

Severe Impact (64 dBA)
64—(81-6)= —11 dB
According to Figure 4-6, the distance correction is approximately -II dB at 265 ft.

Project Level
Ldn
Onset of Moderate
Impact
Distance
Onset of Severe
Impact
Distance
81 dBA
715 ft
265 ft
Draw Noise mpact Contours
Contours can be drawn as in Part I for '/< mile on either side of the grade crossing.

Example 4-2 General Noise Assessment — Highway/Transit
General Noise Assessment Example of Highway/Transit Corridor Projects This example illustrates a highway/transit project where the highway noise dominates and the FHWA assessment methods should be used to inform the FTA process according to the impact criteria in Section 4.I.

Case I: Highway Dominates
A new LRT system is planned for the median of a major highway that carries heavy traffic both day and night.

The noise levels at the first row of houses along the highway were measured during peak hour, mid -day and nighttime with hourly Le,horeadings of 65 dBA, 63 dBA, and 60 dBA, respectively. The LRT tracks will be 125 ft from the first row of houses. The LRT operations during peak hour will be 4 -car trains at 45 mph, with 5 - minute headways in both directions. Nighttime service decreases to 2 -car trains and 20 minute headways.

FTA is providing a share of the funding for the LRT project, but the State DOT and the FHWA are co -lead agencies because the median requires considerable preparation for the tracks, including replacing bridge piers of street crossings and moving some highway lanes.

Assumptions
SELYef = 82 dBA
Nd = 4 cars per train
Nn = 2 cars per train
S = 45 mph
Vd = 24 trains per hour
Vn = 6 trains per hour
Estimate Project Noise Exposure at 50 ft
Use Table 4-9 and Table 4-10 to determine the peak hour Le9(inr) for the rail vehicles.

Use Eq. 4-3 to calculate the LRT peak -hour noise level.

LdRcars(h) = SELTef + 10 log(Ncars) + 201og(So) + 10 log(V) — 35.6 45 = 82 + 10 Log(4) + 20log(50) + 10 log(24) — 35.6
= 65 dBA at 50 ft
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Use Eq. 4-3 to calculate the LRT late evening hourly noise level.

LnBcars(h) = SELref + 10log(Ncars) + 201og(o) + 10log (V) — 35.6 45 = 82 + 10 log(2) + 201og(50) + 10 log(6) — 35.6
= 56 dBA at 50 ft
Estimate Project Noise Exposure at 125 ft
Since the LRT tracks will be 125 ft from the first row of houses, use Figure 4-6 to determine the level at 125 ft.

At 125 ft, the distance correction is 5 dB.

Peak hour:
65 — 5 = 60 dBA at 125 ft
Night hourly:
56 — 5 = 51 dBA at 125 ft
In this case, the highway dominates the noise environment in the area both day and night, by 5 dB during peak hour and 9 dB at night. According to Section 4.1 and Table 4-2, use the FHWA assessment methods.

Example 4-3 General Noise Assessment — BRT System
General Noise Assessment for a BRT System in an Existing Railroad Right -of -Way This example for a simple BRT project illustrates using the FTA procedures for a new BRT corridor planned in an existing abandoned railroad ROW.

Assumptions
SELref = 82 for buses
S =25mph
Vd = (344 buses) / (15 hours) = 22.9 buses per hour
V. = (I 16 buses) / (9 hours) = 12.9 buses per hour
Estimate Project Noise Exposure
Use the information and equations in Table 4-12 to calculate the daytime and nighttime Legiihr) at 50 ft.

Cs = 15 for buses
Ld.Bus
Ln.Bus
S
= SELref + 101og(Vd) + Cslog(50) - 35.6
25 = 82 + 10 log(22.9) + 15log(50) — 35.6
= 55 dBA at 50 ft
= SELref + 10 log (V„) + Cslog(50) - 35.6
25 = 82 + 10 log(12.9) + 15109(50) — 35.6
= 53 dBA at 50 ft
Calculate Ldn at 50 ft for the project using Eq. 4-13.

Ldn.Bus = 101og(15 x 10ltd.Bus/iol + 9 x 1.0((a"B„s+to)/io)) — 13.8 = 60 dBA at 50 ft
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Estimate Existing Noise Exposure
The surrounding area is residential with 2,500 people per square mile starting approximately 100 ft away from the proposed alignment. Determine the existing noise using Table 4-17.

Ldn = 50 dBA
Determine Noise Level and distance for the Onset of Impact Determine the noise level for the onset of moderate and severe impact using Figure 4-2 and the existing noise level of 50 dBA. Note that this project is land use category 2 and the appropriate metric is Ldp.

Existing
Noise
L,
Onset of Moderate Impact
Onset of Severe
Impact
Lan
50 dBA
54 dBA
59 dBA
Determine the distance to the noise impact contours using the fixed -guideway & highway curve in Figure 4-6 (or the equations in Table 4-15) and the project impact thresholds obtained above. The project noise level at 50 ft is approximately 60 dBA.

Moderate impact (54 dBA)
54-60= —6 dB
According to Figure 4-6, the distance correction is approximately -6 dB at 125 ft.

Severe Impact (59 dBA)
59-60= —1 dB
According to Figure 4-6, the distance correction is less than - I dB at approximately 60 ft.

Project Level
Lin
Onset of Moderate
Impact
Distance
Onset of Severe Impact
Distance
60 dBA
125 ft
60 ft
Inventory of Noise Impact
Since there are residential land uses approximately 100 ft away from the proposed alignment and the onset of moderate impact is at 125 ft, there are possible moderate impacts to the residences.

Noise Mitigation
A barrier is proposed for mitigation between the BRT system and the residences. The analysis is repeated and results in a predicted new project level of 55 dBA and the following impact distances:

Mitigated Project
Level
L.

Onset of Moderate
Impact
Distance
Onset of Severe Impact
Distance
55 dBA
60 ft
N/A
With a noise barrier in place between the BRT system and the residences, it is predicted that the onset of moderate impact would occur approximately 60 ft away from the BRT system. Since the residential area begins approximately 100 ft away from the BRT system, which is beyond the distance of moderate impact (60 ft), a noise barrier would provide the appropriate noise mitigation for the predicted moderate impact.

The onset of severe impact is listed as N/A because with a noise barrier, the severe impact criterion is not exceeded by the project.

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Example 4-4 General Noise Assessment — Transit Center
General Noise Assessment for a Transit Center
The following example illustrates the procedure for performing a General Noise Assessment for a stationary source. The example represents a typical FTA-assisted project in an urban area, the siting of a busy transit center in a mixed commercial and residential area, as shown in Figure 4-8.

Assume that the Noise Screening Procedure has already been done for this project and the nearest residence has been identified approximately 140 ft from the center of the proposed transit center. Recall that if any residential or other noise -sensitive land use is identified within 150 ft of a transit center during the Noise Screening Procedure, additional analysis is required.

Assumptions
• Main Street Traffic
Peak hour traffic of 1200 autos, 20 heavy trucks, 300 medium trucks. • Population Density
12 houses per block, single family homes, 3 people per family. o Block area 78,750 square ft.
o Population density = 9,750 people/square mile.
• Bus Traffic
Period
Hours
Buses per
Hour
Peak, Morning
7 a.m.-9 a.m.
30 Peak, Afternoon
4 p.m. -6 p.m.
30 Mid -day
9 a.m.-4 p.m.
15 Evening
6 p.m. -10 p.m.
12 Early Morning (Night)
6 a.m.-7 a.m.
15 Late Night
10 p.m. -I a.m.
4 Estimate Project Noise Exposure at 50 ft
Determine the hourly volume of buses during day and night.

Daytime (7 a.m. - 10 p.m.)
273 buses
Vd = — 18.2 buses/hour
15 hours
Nighttime (I 0 p.m. - 7 a.m.)
27 buses
Vn — — 3 buses/hour
9 hours
Calculate the daytime and nighttime Leg( Ihr) at 50 ft for the bus transit center using the reference levels in Table 4-13 and the equations in Table 4-14.

Ld.BTcenter = SELTe f + CN — 35.6

18.2 = 101 + 10log( 20 ) — 35.6
= 65 dBA at 50 ft
Ln.Brcenter = SELref + CN — 35.6
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3 = 101 + 101og(2O) — 35.6
= 57 dBA at 50 ft
Calculate Ldn at 50 ft for the project using Eq. 4-17.

Ldn.eTcenter = 10log(15 x 10(LdfTcenc=/lp) + 9 x 10(<L".ercenc=+lo)/l0)-13.8 = 66 dBA at 50 ft
Estimate Existing Noise Exposure
Estimate existing noise at noise -sensitive sites from the dominant noise source, and either major roadways or local streets (population density).

Roadway Noise Estimate — The traffic on Main Street qualifies this street for the Other Roadway category in Table 4-I 7. According to the map, the nearest residence is 275 ft from the edge of Main Street. The table shows existing Ldr, = 55 dBA at this distance for representative busy city street traffic.

Population Density Noise Estimate — Noise from local streets is estimated from the population density of 9,750 people/square mile. Table 4-17 confirms that the L. is approximately 55 dBA.

In this example, the existing noise level by both the roadway and population density estimates are the same, but that is not always the case. If the levels are different, use the lower noise level. The existing noise level associated with the residential neighborhood in this example is Ldn = 55 dBA.

Determine Noise Level and Distance for the Onset of Impact Determine the noise level for the onset of moderate and severe impact using Figure 4-2 and the existing noise level of 55 dBA. Note that this project is land use category 2 and the appropriate metric is Ld .

Existing Noise
L.

Onset of Moderate
Impact
Lai
Onset of Severe
Impact
Lm,
55 dBA
56 dBA
62 dBA
Determine the distances from the center of the property to the noise impact contours using the stationary curve in Figure 4-6. The project noise level at 50 ft is 66 dBA.

Moderate impact (56 dBA)
56-66= —10 dB
According to Figure 4-6, the distance correction is approximately -10 dB at 125 ft.

Severe impact (62 dBA)
62 — 66 = —4 dB
According to Figure 4-6, the distance correction is -4 dB at approximately 70 ft.

Project Noise
l.... Impact
Onset of Moderate
Distance
Onset of Severe
Impact
Distance
66 dBA
125 ft
70 ft
Draw Noise mpact Contours
Draw lines at 70 ft and 125 ft from the center of the property of the proposed transit center. These lines represent the noise impact contours. (Note that in Figure 4-8 the severe impact contour is not drawn for clarity. The contour is just within the dashed line representing the moderate impact contour after mitigation).

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Inventory of Noise Impact
Within, or touching, the contour defining moderate impact are three residential buildings (shaded in Figure 4-8). No residences are within the severe impact contour.

Noise Mitigation
The process is repeated with a hypothetical noise barrier at the property line on the residential side of the transit center. This would consist of a wall approximately 15 ft high partially enclosing the transit center, sufficient to screen the residences but not the commercial block facing Main Street. According to Table 4-14, the approximate noise barrier effect is -5 dB. Repeating the procedure above, the noise barrier will reduce the moderate impact contour to 80 ft and the severe impact contour to 45 ft (note that at 50 ft the distance correction is 0), which in this example eliminates all potential impacts on the residences.

JI a IMPACTED RESIDENCES

SCALE IN FEET
400
Figure 4-8 Example of Project for General Noise Assessment:

Siting of Transit Center in Mixed Commercial/Residential Area Moderate Impact'
Noise Contour
With Mitigation
Proposed
Transit Center9
Bus Parking
Moderate Impact
Noise Contour
Without Mitigation
ccA

4.5 Evaluate Impact: Detailed Noise Analysis
Evaluate for impact using the Detailed Noise Analysis procedure in this section, if appropriate. For guidelines on when the Detailed Noise Analysis is appropriate, review Section 4.2.

The steps in the Detailed Noise Analysis (Figure 4-9) parallel the steps in the General Noise Assessment, though the Detailed Noise Analysis employs equations for computations rather than graphs or tables. Each step in the Detailed Noise Analysis is more refined in the prediction of project noise and subsequent evaluation of mitigation measures. Noise projections from the project must be determined for each receiver.
• Step I: Identify Noise -Sensitive Receivers
Identify the noise -sensitive receivers of interest in the impact analysis study, including clustering noise -sensitive areas. This identification is usually based FEDERAL TRANSIT ADMINISTRATION 64
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on the Screening Procedure and General Noise Assessment previously conducted.
• Step 2: Determine Project Noise Source Reference Levels Determine the project noise sources and reference levels. Then, estimate the project noise exposure at the reference distance of 50 ft, considering operational characteristics. When appropriate, measurements may be used to determine noise source reference levels.
• Step 3: Determine Propagation Characteristics
Estimate project noise exposure as a function of distance, accounting for shielding and propagation along the path.
• Step 4: Combine Noise Exposure from All Sources
Combine all sources to predict the total project noise at receivers. ■ Step 5: Determine Existing Noise Exposure
Determine the existing noise exposure. Measurements are used to determine the existing noise exposure. When measurements are unavailable, a simplified procedure to estimate existing noise exposure may be used with a clear justification to and approval by the FTA Regional office. ■ Step 6: Assess Noise Impact
Assess the noise impact at each receiver of interest using separate procedures for transit only and multimodal transportation projects. • Step 7: Determine Noise Mitigation Measures
Evaluate the need for mitigation and repeat the Detailed Noise Analysis with proposed mitigation.

When situations arise that are not explicitly covered in the Detailed Noise Analysis, professional judgment, in consultation with the FTA Regional office, 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.

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Receiver of Project
Interest Sources
Operational Propagation
Characteristics Characteristics
Reference
SEL. 50 ft
Ldn, 50 ft
Leq, 50 ft
Exposure vs
Distance
`Curve�
Project
Noise
Noise Impact
Criteria
Noise
Impact
Yes
Mitigation
Required?
Remaining
Noise Impact
Study Area
Characteristics
Existing
Noise
Figure 4-9 Procedure for Detailed Noise Analysis
Step I: Identify Noise -Sensitive Receivers
Select the noise -sensitive receivers of interest, the number of which will depend upon the land use in the vicinity of the proposed project and the extent of the study area defined by the Noise Screening Procedure in Section 4.3 and the results of the General Noise Assessment in Section 4.4.

The steps in identifying the noise -sensitive receivers of interest, both the number of receivers needed and their locations, shown in Figure 4- 10, include:

I a. Identify all noise -sensitive land uses.
b. Select individual receivers of interest.
c. Cluster residential neighborhoods and other large noise -sensitive areas.

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Identified Noise
Impacted Sites
Sources of
Land Use Information
Buildings
Used by Public
Isolated
Residences
Small
Outdoor
Areas
Select
Every Site
Residential
Neighborhoods
Large
Outdoor
Areas
Subdivide
Into
Clusters
rEacSite
In h
Cluster
Figure 4-10 Guide to Selecting Noise -Sensitive Receivers of Interest I a. Identify all noise -sensitive land uses where impact is identified by the General Noise Assessment in Section 4.4. If a General Noise Assessment has not been done, include all noise -sensitive sites according to the Noise Screening Procedure in Section 4.3. In areas where ambient noise is low, include land uses that are farther from the proposed project than for areas with higher ambient levels.

Recommended materials and methods that can assist in locating noise -sensitive land uses near the proposed project include:
• Land use maps prepared by regional or local planning agencies or by the project staff. Area -wide maps often do not have sufficient detail to be of much use. But they can provide broad guidance and may suggest residential pockets hidden within otherwise commercial zones. Of more use are project -specific maps that provide building -by -building detail on the land near the proposed project.
• Road and town maps can supplement other maps, are generally more up- to-date, and may be of larger scale.
• Aerial photographs, when current, especially those of 400 -ft scale or better, are valuable in locating all potential noise -sensitive land uses close to the proposed project. In addition, they can be useful in determining the distances between receivers and the project.
• Windshield survey, in which the corridor is driven and land uses are annotated on base maps, may be used for definitive identification of noise - sensitive sites. The windshield survey, supplemented by footwork where needed, is especially useful in identifying newly -constructed sites and in confirming land uses very close to the proposed project. In addition, maps and aerial photos typically reveal only horizontal distances, not vertical distances. Houses on a hill overlooking the project may need a barrier of unacceptable height for its attenuation to be effective, and the greater vertical distance between source and receiver may eliminate the impact entirely. The windshield survey would reveal where vertical contour maps FEDERAL TRANSIT ADMINISTRATION 67
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or other means may be needed so that vertical distances can be determined.
• Geographic Information Systems (GIS) provides electronic mapping needed for identifying noise -sensitive land uses. GIS data may include land parcels, building structures, aerial photography, and project -specific information. These data may be obtained during the project study or from local or regional agencies that store and maintain GIS data. Using electronic GIS data has advantages over paper mapping with respect to automating the process of identifying noise -sensitive land uses and accurately being able to determine their distances to the project alignment
Table 4-18 contains three types of land uses of interest and provides guidelines as to when receivers should be analyzed individually and when they can be clustered.

Table 4-I8 Land Uses of Interest
Land Uses
Specific Use
Selecting Receivers
Residences
Isolated single family residences
Neighborhoods (single and
multi -family residences,
apartment buildings, duplexes,
etc.)
Select each isolated residence as a receiver of interest.

For residential areas, cluster by proximity to project
sources, proximity to ambient -noise sources, and location along project line. Choose one receiver of interest
(closest to the project noise source and at an
intermediate distance from the predominant sources of
existing noise) in each cluster (i.e., Balance the distance between the receiver and the new noise source and the
receiver and the existing noise source). Multiple clusters in one location may be needed to fully characterize the area.

Indoor noise-
sensitive sites
Places of worship
Schools Hospitals/nursing
homes Libraries
Public meeting halls
Concert
halls/auditoriums/theaters
Recording/broadcast studios
Museums and certain historic
buildings
Hotels and motels
Other public buildings with
noise- sensitive indoor use
Select noise -sensitive buildings as separate receivers of interest.

Outdoor noise-
sensitive areas
Certain parks
Historic sites used for
interpretation
Amphitheaters
Passive recreation areas
Cemeteries
Other outdoor noise -sensitive
areas
For relatively small noise -sensitive areas, select noise - sensitive sites as separate receivers of interest.

For relatively large areas (e.g. a cemetery, etc.), cluster by proximity to project noise sources, proximity to ambient - noise sources, and location along project line. Choose one receiver of interest (closest to the project noise source and at an intermediate distance from the predominant
sources of existing noise) in each cluster.

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I b. Select the following types of noise -sensitive receivers within the noise study area, per Table 4-18, to be evaluated as individual receivers:
• Every major noise -sensitive public building
• Every isolated residence
• Every relatively small outdoor noise -sensitive area
Use judgment to avoid analyzing noise where such analysis is obviously not needed. Areas that are considered particularly noise -sensitive by the community, but do not meet the criteria in Table 4-3, should be considered on a case -by -case basis as discussed in Section 4.1.

I c. Residential neighborhoods and relatively large outdoor noise -sensitive areas can often be clustered, simplifying the analysis that is required without compromising the accuracy of the analysis. Subdivide all such neighborhoods/areas into clusters of approximately uniform noise, each containing a collection of noise -sensitive sites. Strive to obtain uniformity of both project noise and ambient noise using the following guidelines:
• In general, project noise reduces (drops off) with distance from the project.

For this reason, project noise uniformity requires nearly equal distances between the project noise source and all sites within the cluster. Clusters are typically shaped as long narrow strips parallel to the transit corridor and/or circling project point sources such as maintenance facilities. It is suggested to cluster sites where the project noise varies over a range of 5 dB or less.
• Note that noise drops off approximately 3 dB per doubling of distance for line sources and approximately 6 dB per doubling of distance for point sources over open terrain. This reduction in noise will occur over a shorter distance in areas containing obstacles blocking the path of sound propagation, such as rows of buildings.
• Ambient noise usually drops off from non -project sources in the same manner as noise from project sources. For this reason, clustering for uniform ambient noise will usually result in long narrow strips parallel to major roadways or circling major point sources of ambient noise, such as manufacturing facilities. It is suggested to cluster sites where the ambient noise varies over a range of 5 dB or less. Ambient noise levels may be difficult to judge without measurements. In areas without predominant sources of noise, like highways, ambient noise can be considered to vary with population density, which is often uniform along the corridor. In situations where ambient noise tends to be uniform, the clusters can encompass relatively large areas.

After defining clusters, select one representative receiver in each cluster. It is recommended to choose the receiver closest to the project noise source and at an intermediate distance from the predominant sources of existing noise. See Appendix D for additional guidance and examples on clustering receivers, as well as an example.

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Assess each identified cluster representative and individual noise -sensitive receiver of interest using the Detailed Noise Analysis as presented in the following steps.

Step 2: Determine Project Noise Source Reference Levels Identify the major project noise sources near the noise -sensitive receivers of interest, group them by source type, and determine reference levels to compute project noise at 50 ft, as shown in Figure 4-1 I.

Receivers of
Interest
Project noise
Sources
Separate Sources
by Source Type
Fixed -guideway
Sources
HighwayrTransit
Sources
Operating
Parameters
Stationary
Sources
Figure 4-I I Flow Diagram for Determining Project Noise at 50 ft 2a. Identify the major project noise sources near receivers of interest according to Table 4-19. The right-hand column of the table indicates if each source is considered as a major contributor to the overall noise impact. Note that some noise sources can create high noise levels but are not indicated as major contributors. Although such sources are loud, they rarely stay in a neighborhood for more than a day or two; therefore, the overall noise exposure is relatively minor. Computations are required for all major noise sources in this table.

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Table 4-19 Sources of Transit Noise
Project Type
Source Type
Actual Source
Major?
Commuter Rail
Light Rail Streetcars
RRT
Fixed -Guideway
Locomotive and rail car passbys
Horns and whistles
Crossing signals
Crossovers/switches
Squeal on tight curves
Track -maintenance equipment
Yes
Yes
Yes
Yes
Yes
No
Stationary
Substations
Chiller plants
Yes
No
Busways
Bus Transit Malls
Highway/Transit
Bus passbys
Buses parking
Yes
No
Stationary
Buses idling
Yes
AGT
Monorail
Fixed -Guideway
Vehicle passbys
Yes
Miscellaneous
Line equipment
No
Terminals
Stations
Transit Centers
Fixed -Guideway
Locomotive and rail car passbys
Crossovers/switches
Squeal on tight curves
Yes
Yes
Yes
Highway/Transit
Bus passbys
Buses parking
Automobile passbys
Yes
No
No
Stationary
Locomotives idling
Buses idling
Ferry boats landing, idling, and departing at dock
HVAC equipment
Cooling towers
P/A systems
Yes
Yes
Yes
No
No
No
Park -and -Ride Lots
Highway/Transit
Bus passbys
Buses idling
Automobile passbys
Yes
Yes
No
Stationary
P/A systems
No
Traffic Diversion Projects
Highway/Transit
Highway vehicle passbys
Yes
Storage Facilities
Maintenance Facilities
Fixed -Guideway
Locomotive and rail car passbys
Locomotives idling
Squeal on tight curves
Horns, warning signals, coupling/ uncoupling,
auxiliary equipment, crossovers/ switches, brake
squeal, and air release
Yes
Yes
Yes
Yes
Highway/Transit
Bus passbys
Yes
Stationary
Buses idling
Yard/shop activities
Car washes
HVAC Equipment
P/A Systems
Yes
No
No
No
No
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2b. Separate the major noise sources by source type: fixed -guideway transit, highway/transit or stationary facility. Note that a major fixed -guideway system will usually have stationary facilities associated with it, and that a stationary facility may have highway/transit elements associated with it. Then use the instructions in the following source type options below to:
2c. Determine the source reference levels for the all project noise sources.

Each source reference level pertains to reference operating conditions for stationary sources or one vehicle passby under reference operating conditions.

These reference levels should incorporate source -noise mitigation only if such mitigation will be considered for incorporation into the system specifications.

The source levels used in this manual are typical of systems designed according to current engineering practice, but they do not include special noise control features that could be incorporated in the specifications at extra cost. If special features that result in noise reductions are included in any of the predictions, the Federal environmental documents must include a commitment by the project sponsor to adopt such treatments before the project is approved for construction. For example, if the specifications include vehicle noise limits that may not be exceeded, these limits should be used to determine the reference level, and this level should be used in the analysis rather than the standard, tabulated reference level.
2d. Convert the source reference level to noise exposure in terms of Leq(Ihr) or La" under project operating conditions using the appropriate equations depending upon the type of source. The noise exposure is determined at the reference distance of 50 ft.

Option A. Fixed -guideway Sources — Compute project noise at 50 ft for fixed -guideway sources as identified in the second column of Table 4-19.

A.i. Reference SEL Levels
Determine the reference SEL at 50 ft for each major fixed -guideway noise source, either by measurement according to Appendix F or by referencing Table 4-20. The table provides guidance on which method is preferred for each source type. The "NO" designation implies that the source levels given in the table are appropriate to use in the analysis, and the "YES" designation implies that measurements are preferred over the data given in the table. In general, measurements are preferred for source types that vary considerably from project to project, including any emerging technology sources. The data in the table are adequate for source types that do not vary considerably from project to project.

For sources where measurements are preferred, refer to Appendix F for guidance on measurement procedures and methods for conversion of these measurements to the reference conditions of Table 4-20. For projects where source -noise specifications have been defined (e.g., noise limits are usually included in the specifications for purchase of new transit vehicles), these specifications may be used instead of measurements after conversion to reference conditions using the equations in Appendix F. This is only appropriate when there is a firm commitment to adopt the noise specifications in the vehicle FEDERAL TRANSIT ADMINISTRATION 72
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procurement documents during the engineering phase and to adhere to the specifications throughout the procurement, delivery, and testing of the vehicles.

Approximate L,"„, values are provided in the table for general user information.

As discussed in Appendix B.I.4.2, L",,, is not used directly in the evaluation of noise impact.

Table 4-20 Source Reference SELs at 50 ft: Fixed -Guideway Sources at 50 mph Source
Reference
SEL, dBA
Approximate
L,,,ax, dBA
Prefer
Measurements? *
Rail cars
82 80
No
Streetcars**
76 74
No
Locomotives — diesel
92 88
No
Locomotives — electric
90 86
No
Diesel multiple unit (DMU)
85 81
Yes
Agt — steel wheel
80 78
Yes
Agt — rubber tire
78 75
Yes
Monorail
82 80
Yes
Maglev
72 70
Yes
Transit car horns (emergency)
93 90
No
Transit car whistles
8l
78 No
Locomotive horns
At -grade crossing
113
110
No
From crossing to 1/8 mile
110
From 1/8 mile to 1/4 mile
110
110
* "No" implies that the source levels given in the table are appropriate to use in the analysis and "Yes" implies that measurements are preferred over the data given in the table. **The reference speed for streetcars is 25 mph. For streetcar speeds above 25 mph, use the "Rail Cars" reference level and 50 mph for the reference speed. t Use the following equation for locomotive horns from crossing to 1/8 mile:

SELRef=113-3x(°)
fifi0
where:

DP= distance from grade crossing parallel to tracks
A.ii. Estimate Noise Exposure at 50 ft — Use the reference SELs in Table 4-20, operating conditions, and the equations in Table 4-2 I to predict the noise exposure at 50 ft expressed in terms of Leg(' hr.) and Ld,,. Follow the steps below:

I. Identify operating conditions — Trains with different numbers of cars or operating conditions produce different noise exposure levels and should be converted from SEL to Ldn separately. Use the following guidelines to determine if sources should be converted separately. These differences in operating conditions will produce an approximate 2 -decibel change in noise exposure:
• 40 percent change in number of locomotives or cars per train. • 40 percent change in number of trains per hour.
• 40 percent change in number of trains per day, or per night (for computation of Ldp,).
• I5 percent change in train speed.
• Change of one notch in diesel locomotive throttle setting (e.g., from notch 5 to notch 6).

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2. Establish relevant time periods — For each of these source types and conditions, determine the relevant time periods for all receivers that may be affected by this source.
• For residential receivers, the time periods of interest for computation of Lan are: daytime (7 a.m. to I O p.m.) and nighttime (10 p.m. to 7 a.m.).
• If the source will affect non-residential receivers, the time period of interest is the loudest hour of project -related activity during hours of noise sensitivity. Several different hours may be of interest for non-residential receivers depending on the hours the facility is used.

3. Collect input data
• Source reference SELs for locomotives, rail cars, and warning horns. • Number of rail cars in the train (if this number varies during the day, take the average for the daytime and nighttime periods separately for category 2 land uses, and use the maximum number during the period of interest for category I or 3 land uses). • Number of locomotives in the train, if any.
• Train speed, in miles per hour (maximum expected).
• Average throttle setting of the train's locomotive(s) for diesel - powered locomotives and DMU's only.(") If this input is not available, assume a throttle setting of 8 for locations where the vehicle would accelerate and 5 for all other locations.(25) • For residential receivers of interest:
▪ Average hourly train volume during daytime hours (the total number of train passbys between 7 a.m. and 10 p.m., divided by 15 hours);
▪ Average hourly train volume during nighttime hours (the total number of train passbys between I O p.m. and 7 a.m., divided by 9 hours);
• For non-residential receivers of interest, number of events that occur during each hour of interest in trains per hour; and • Track type (continuously welded or jointed) and profile (at -grade or elevated).

4. Calculate Leq(ihr) at 50 ft
• Calculate Leq(Ihr) using the appropriate equations in Table 4-2 I for each hour of interest.
• Compute the combined Leq(Ihr). It may be necessary to compute the combined totals with and without the warning horns; some neighborhoods along the corridor may be exposed to the horn noise and some may not.

5. Calculate Lan at 50 ft
• If the project noise will affect any residential receivers, calculate the La„ using the combined day Leq(Ihr) and the combined night Leq(Ihr). • It may be necessary to calculate Lan with and without the warning horns, as above.

Omit this term if not applicable from the equation in Table 4-21 for other vehicle types.

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Note that the equations in Table 4-21 include terms to account for a difference in speed from the reference speed of 50 mph and a numerical adjustment to account for the one -hour time period for this metric. For more information on the numerical adjustment to represent the time period of interest, see Appendix B. 1.4.4.
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Table 4-2I Computation of Le9(Inr) and Lda at 50 ft: Fixed -Guideway Sources Locomotives*
Leq(mr)at 50 ft
S
Leg.Loco(1hr) = SELref + 10log(NLoco) + CT + Klog(50) + 101og(V) — 35.6 Eq. 4-25 Locomotive
Warning
Horns**
Los('h )at 50 ft
L eq.LHorns(1hr) — SEL ref + 10 log ) — 35.6 Eq. 4-26
o
Rail Vehiclest
Lq(mr)at 50 ft
S
Leq.ecars(ihr) = SELref + 10log(Ncars) + 201og(S0) + 10 log(V) — 35.6 Eq. 4-27 + Adjtrack
Streetcar
(25 mph or slower)
Leo hr)at 50 ft
Leq.scars(1hr) = SELref + 1.0log (Ncars) + 21og(25 E.4-28) + 10log(V) — 35.6 + Adjtrack Eq.

Transit
Warning
Horns**
Leq(mr)at 50 ft
L + 10 log(V) 35.6 Eq. 4-29
SEL S
eq.Txorns(1hr) = ref — 10 to 9(50) 9( ) —
Combined Locomotive
transittt
Leq(Ihr)at 50 ft
L 1010 (/10(Leq.Loco(ihr)/10) + 10(Leg.kcars(ihr)/So)
eq.combo(1hr) = g\ q E 4-30
+ 10( Lagscars(ihr)/10) + 10(L""" o t(1hr)/10) + 10( LeqTHarns(ihr)/10) Daytime
La at 50 ft
L L where V = Vd, Ntoeo = Nd loco events), and Nc r = Nd(car events) Eq. 4-3 d = eq(ihr) ( )
Nighttime
Ln at 50 ft
Ln = Leq(lhr) where V = V„, and NL.,.a = Nd (Ioco events), and Noers = Nd (car Eq. 4-32 events)
Day/Night fightLdn t
Ldn = 101og(15 X 10(Ld/lo) + 9 X 10((Ln+1o)/10)) - 13.8 Eq. 4-33 NLoco = average number of locomotives per train
CT =0for T www.fra.dotgov/Elib/Document/268I
t Includes all commuter rail cars, transit cars, streetcars above 25 mph, AGT and monorail. tt Only include appropriate terms.

T Because of the wide range of vehicle types that qualify as a DMU, measurements are preferred for the reference level and speed coefficient. If no measurements are conducted, use the reference level in Table 4-20 and a speed coefficient of 0.

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Example 4-5 Detailed Noise Analysis — Fixed Guideway Noise Sources Computation of Leq(ihr) and Len at 50 ft for Fixed -Guideway Source A commuter train with I diesel locomotive and 6 cars will pass close to a residential area at a grade crossing.

The track is jointed.

Assumptions
SELTef = 92 for diesel locomotives
= 82 for rail cars
= 113 for locomotive warning horns at -grade crossing
Ncars = 6
NLoco = I
S = 43 mph
T =8
Vd = 40 trains/15 hours = 2.667 trains per hour
Vn = 2 trains/9 hours = 0.222 trains per hour
Use the equations in Table 4-21 to determine the daytime Leq(onr) for each source and the combined daytime Leg(ihr) at 50 ft.

Ld.Locs(1hr)
Ld.RCars(lhr)
= SELYe f + 10log (NLoco) + CT + Klog(50) + 101og(Vd) — 35.6 43 = 92 + 10 log(1) + 6 + (-10)1og(50) + 10109(2.667) — 35.6 = 67.3 dBA at 50 ft
= SELref + 10109(NCars) + 201og (SO ) + 10log (Vd) — 35.6 +Adjtrack 43 = 82 + 10 log(6) + 201og (5O) + 10 log(2.667) — 35.6 + 5 = 62.1 dBA at 50 ft
Ld.LHorn(lhr) = SELTef + 10log (Vd) — 35.6
= 113 + 10 log(2.667) — 35.6
= 81.7 dBA at 50 ft
Ld.Combo (1hr)
With horn:

Without horn:
r Ld.locos(lhr) Ld.RCars(lhr) Ld.LHorn(1hr)
= 1010g10( 110) + 10( X10) + 10( /10)l
= 81.9 dBA in neighborhoods where the horn is sounded J = 101og [lo(LdL°c°s(1hr)/10, + 10(La
RCars(ihr)/l0)1
= 68.4 dBA in neighborhoods where the horn is JJ not sounded Use the same equations as above to determine the nighttime Leq(ihr)at 50 ft. Use Vn instead of Vd. = 56.5 for locomotives
Ln.Locos(1hr)
= 51.3 for cars
Ln.RCars(1hr)
= 70.9 for horns
Ln.LHorn(1hr)
= 71.1 in neighborhoods where the horn is sounded
Ln.combo(1hr)
= 57.6 in neighborhoods where the horn is not sounded
Calculate the Ldn with and without horns.

Ldn.combo = 10log [15 x 10(LdC°mb°/10) + 9 x 10((L„c°mb°+1o)/10)1 - 13.8 FEDERAL TRANSIT ADMINISTRATION 77
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With horn: = 81.6 at 50 ft in neighborhoods where horns are sounded Without horn: = 68.1 at 50 ft in neighborhoods where horns are not sounded Note: Computation results should always be rounded to the nearest decibel at the end of the computation. In all examples of this section, however, the first decimal place is retained for readers to precisely match their own computations against the example computations.

Option B. Highway/Transit Sources — Compute project noise at 50 ft for highway/transit noise sources as identified in the second column of Table 4-19.

Use the instructions below to estimate source noise levels for projects following FTA's procedures that involve highway vehicles.

This method is based on the original FHWA highway noise prediction model, with updated noise emission levels.(26) The vehicle equations are applicable to speeds typical of freely -flowing traffic on city streets and access roads.

B.i. Reference SEL Levels — Determine the reference SEL at 50 ft for each major highway/transit source, either by measurement according to Appendix F or by using Table 4-22.(v) The table provides guidance on which method is preferred for each source type. "NO" implies that the source levels given in the table are appropriate to use in the analysis, and "YES" implies that measurements are preferred over the data given in the table. For sources where measurements are preferred, refer to Appendix F for guidance on measurement procedures and methods for conversion of measurement data to the reference conditions in Table 4-20.

Approximate L. values are provided in the table for general user information.

As discussed in Appendix B.I.4.2, Lm, is not used directly in the evaluation of noise impact.

Table 4-22 Source Reference SELs at 50 ft: Highway/Transit Sources at 50 mph Source
Reference
SEL, dBA
Approximate
L,",,, dBA
Prefer
Measurements?*
Automobiles
74 70
No
Buses (diesel)
82 79
No
Buses (electric trolleybus)
80 77
No
Buses (hybrid)**
83 80
Yes
*"No" implies that the source levels given in the table are appropriate to use in the analysis and "Yes" implies that measurements are preferred over the data given in the table. ** Hybrid bus with full-time diesel engine and electric drive motors.

Idling buses are considered stationary sources.

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B.ii. Noise Exposure at 50 ft — Use the reference SELs in Table 4-22, operating conditions, and the equations in Table 4-23 to predict the noise exposure at 50 ft expressed in terms of Leq(Ihr) and Ldn. Follow the steps below:

I. Identify operating conditions — Noise emission from most transit buses is not dependent upon whether the buses are accelerating or cruising.

However, accelerating suburban buses are substantially louder than cruising suburban buses. For this reason, suburban buses require separate calculation along roadway stretches where they are accelerating. Separate calculation is also needed for all highway/transit vehicles at different speeds, since speed affects noise emissions. Use the following guidelines to determine if sources should be calculated separately. These differences in operating conditions will produce an approximate 2 -decibel change in noise exposure:
• 40 percent change in number of vehicles per hour;
■ 40 percent change in number of vehicles per day, or per night (for computation of Ld„); or
• 15 percent change in vehicle speed.

2. Establish relevant time periods — For each of these source types and conditions, determine the relevant time periods for all receivers that may be affected by this source.
• For residential receivers, the time periods of interest for computation of Ldn are: daytime (7 a.m. to I O p.m.) and nighttime (10 p.m. to 7 a.m.).
• If the source will affect non-residential receivers, the time period of interest is the loudest hour of project related activity during hours of noise sensitivity. Several different hours may be of interest for non-residential receivers depending on the hours the facility is used.

3. Collect input data
• Source reference SELs for the vehicle types of concern • Average running speed in miles per hour
■ For residential receivers of interest:
▪ Average hourly vehicle volume during daytime hours (total number of vehicle passbys between 7 a.m. and I O p.m., divided by 15).

Average hourly vehicle volume during nighttime hours (total number of vehicle passbys between I O p.m. and 7 a.m., divided by 9).
• For non-residential receivers of interest, number of events that occur during each hour of interest, in vehicles per hour

4. Calculate Lego hr) at 50 ft — Calculate Leg(' hr) using the appropriate equations in Table 4-23 for each hour of interest.

5. Calculate Lan at 50 ft — If the project noise will affect any residential receivers, calculate the Ldn using the day Leq(Ihr) and night Leq(Ihr)• Note that the equations in Table 4-23 include terms to account for a difference in speed from the reference speed of 50 mph and a numerical adjustment to FEDERAL TRANSIT ADMINISTRATION 79
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account for the one -hour time period for this metric. For more information on the numerical adjustment to represent the time period of interest, see Appendix B.I.4.4.

Table 4-23 Computation of Leq(,nr) and Ldn at 50 ft: Highway/Transit Sources Leg( ihr) at 50
ft
+ o — o S 35.6 Eq. 4-34
Leq(lhr) = SEL ref 10 log /V � + C emissions 101 g(0)
Daytime
Ld at 50 ft

Ld = Leq( 1hr) where V = Vd Eq. 4-35
Nighttime
L�at50 ft
4= Leq(lhr) where V = V„ Eq. 4-36
Ldn at 50 ft

/
II
Ldn = 10log(15 x 10(Ld/10) + 9 X 10((Ln+lo)'lo)) _ 13 8 Eq. 4-37 Adjustments
= -3 for automobiles, open -graded asphalt
+3 for automobiles, grooved pavement
v
Cemissions
5 Vd
V,
= average hourly volume of vehicles, vehicles per hour
= 251og(so) for buses
311og(So) for hybrid buses (23)

1.6 for accelerating 3 -axle commuter buses
401og(so) for automobiles
= average vehicle speed, mph (distance divided by time, excluding stop time at red lights)
= average hourly daytime volume of vehicles of this type, vehicles per hour total vehicle volume, 7 a.m. to 10 p. m.
15 = average hourly nighttime volume of vehicles, vehicles per hour total vehicle volume,10 p. m. to 7 a.m.
9 Example 4-6 Detailed Noise Analysis — Highway Transit Noise Sources Computation of Led( Ihr) and Ldn at 50 ft for Highway/Transit Source A bus route with city buses will pass close to a school that is in session from 8 a.m. to 4 p.m. on weekdays.

Within this time period, the hour of greatest activity for this bus route is 8 a.m. to 9 a.m.

Assumptions
SELref = 82 dBA
S =40mph
V = 30 buses per hour
Use the equations in Table 4-23 to determine the hourly Legiihr) at 50 ft.

Ld.Bns = SEL + 10 to V + C — 1010 ( 35.6
ref gl ) emissions g\S0)
40 40
= 82 + 10 Log(30) + 6 + 25 x log(50) — 101og(50) — 35.6 = 59.7 dBA at 50 ft
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This same bus also passes close to a residential area with the following operating conditions:

Vd = 200 buses/15 hours = 13.33 buses per hour
Vn = 20 buses/9 hours = 2.22 buses per hour
Calculate the daytime and nighttime Leq(ihr) at 50 ft.
40 40
LdBus = 82 + 10 log(13.33) + 6 + 25 x log(50) - 101og(50) — 35.6 = 56.2 dBA at 50 ft
40 40
L„ Bus = 82 + 10 log(2.22) + 6 + 25 x log(0) — 101og(50) — 35.6 = 48.4 dBA at 50 ft
Calculate Ld„ at 50 ft.

L = lOlog(15 x 10(LdBu'110) + 9 x 10((LnBus+1°)/10)) — 13.8 dn.Bus
= 57.2 dBA at 50 ft
Note: Computation results should always be rounded to the nearest decibel at the end of the computation. In all examples of this section, however, the first decimal place is retained for readers to precisely match their own computations against the example computations.

Option C. Stationary Sources — Compute project noise at 50 ft for stationary sources as identified in the second column of Table 4-19.

C.i. Determine Reference SEL Levels — Determine the reference SEL at 50 ft for each major stationary source, either by measurement according to Appendix F or by using Table 4-24. The table provides guidance on which method is preferred for each source type. "NO" implies that the source levels given in the table are appropriate to use in the analysis, and "YES" implies that measurements are preferred over the data given in the table. In general, measurements are preferred for source types that vary considerably from project to project. For example, curve squeal is highly variable depending on weather conditions, curve radius, and train speed. The data in the table are adequate for source types that do not vary considerably from project to project (crossing signals, for example). For sources where measurements are preferred, refer to Appendix F for guidance on measurement procedures and methods for conversion of these measurements to the reference conditions of Table 4-24.

Layover facilities and transit centers can be the sources of low -frequency noise from idling diesel engines. Sounds with considerable low -frequency components can cause greater annoyance than would be expected based on their A - weighted levels. Low -frequency sounds often cause windows and walls to vibrate resulting in secondary effects in buildings such as rattling of dishes in cupboards and wall -mounted pictures. The reference levels in Table 4-24 are adjusted to take increased annoyance into account. For a Detailed Noise Analysis at locations where such idling takes place for an extended period, use the method described in ANSI Standard S I 2.9 -Part 4, Annex D.(27) Approximate Lmax values are provided in the table for general user information.

As discussed in Appendix B.I.4.2, Lax is not used directly in the evaluation of noise impact.

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Table 4-24 Source Reference SELs at 50 ft: Stationary Sources Source
Reference
SEL, dBA
Approximate
L,,,,,,, dBA
Prefer
Measurements?*
Auxiliary Equipment
I 0
65 Yes
Locomotive Idling
109
73 No
Rail Transit Idling
106
70 No
Buses Idling
I I I
75 No
Ferry Boat Landing**, Idling, and Departing
91 78
No
Ferry Boat Fog Horn
90 84
No
Track Curve Squeal
136
100
Yes
Car Washes
I II
75 Yes
Crossing Signals
I09
73 No
Substations
99 63
No
* "No" implies that the source levels given in the table are appropriate to use in the analysis, and "YES" implies that measurements are preferred over the data given in the table. **Ferry boat landings are included in the stationary source category because the noise from the landing remains in one area even though the boats move in and out.

C.ii. Estimate Noise Exposure at 50 ft — Use the reference SELs in Table 4-24, operating conditions, and the equations in Table 4-25 to predict the noise exposure at 50 ft expressed in terms of Leq(Ihr) and Lan. Follow the steps below:

I. Identify operating conditions — Identify actual source durations and numbers of events. Sources with different operating conditions should be converted from SEL to Ldn separately. Use the following guidelines to determine if sources should be converted separately. These differences in operating conditions will produce an approximate 2 -dB change in noise exposure:
• 40 percent change in event duration (e.g., from 30 to 42 minutes), or
• 40 percent change in number of events per hour (e.g., from 10 to 14 events per hour).

2. Establish relevant time periods — For each of these source types and conditions, determine the relevant time periods for all receivers that may be affected by this source.
• For residential receivers, the time periods of interest for computation of Ldn are: daytime (7 a.m. to I O p.m.) and nighttime (10 p.m. to 7 a.m.).
• If the source will affect non-residential receivers, the time period of interest is the loudest hour of project related activity during hours of noise sensitivity. Several different hours may be of interest for non-residential receivers depending on the hours the facility is used.

3. Collect input data
• Source reference SELs for each relevant source
• Average duration of one event, in seconds
• For residential receivers of interest:

Average number of events per hour that occur during the daytime (the total number of events between 7 a.m. and I O p.m., divided by I5).

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▪ Average number of events per hour that occur during the nighttime (the total number of events between I O p.m. and 7 a.m., divided by 9).
• For non-residential receivers of interest, number of events that occur during each hour of interest in events per hour

4. Calculate Leg('hr)at 50 ft — Calculate Leq(Ihr) using the appropriate equations in Table 4-25 for each hour of interest.

5. Calculate Ldn at 50 ft — If the project noise will affect any residential receivers, calculate the Ldr, using the day Leq(Ihr)and night Leq('hr)• Note that the equations in Table 4-25 include a numerical adjustment to account for the one -hour time period for this metric. For more information on the numerical adjustment to represent the time period of interest, see Appendix B.I.4.4.

Table 4-25 Computation of Leq(Ihr) and Ldn at 50 ft: Stationary Sources Leq(inr> at 50
ft
E 35.6
L SEL 10 log(N) 1010
Eq. 4-38
+ + )
eq(lhr) = ref 9( ) -3600
Daytime
Ld at 50 ft
Ld = Le 1hr where N = Nd
v(
Eq. 4-39
Nighttime
Ln at 50 ft
Ln = Le lhr where N = Nn
e(
Eq. 4-40
Lae at 50 ft
((Ln+lo)/1O)) - 13 8
Lan = 101og(15 x 10(Ld/10) + 9 x 10 h
Eq. 4-41
N
E*
Nd
Nn
= number of events of this type that occur during one -hour = duration of one event, sec
= average hourly number of events that occur during daytime (7 a.m. to 10 p.m.)
number of events between 7 a.m. to 10 p. m.
15 = average hourly number of events that occur during nighttime (10 p.m. to 7 a.m.)
number of events between 10 p.m. to 7 a.m.
9 *Omit the term containing E for ferry boat, and fog horn noise sources.

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Example 4-7 Detailed Noise Analysis — Stationary Noise Sources Computation of Leq(in,>and Ldfl at 50 ft for Stationary Sources A signal crossing lies close to a school that is in session from 8 a.m. to 4 p.m. on weekdays. Within this time period, the hour of greatest activity for the signal crossing is 8 a.m. to 9 a.m.

Assumptions
SELre f = 109 dBA
E = 25 seconds (counting both cycles of the signal)
N = 22
Use the equations in Table 4-25 to determine the hourly Leglin,) at 50 ft.

Ld.Cross
= SELref + 10log(N) + 101og (3600) - 35.6
25 = 109 + 10109(22) + 10log(3600) — 35.6
= 65.2 dBA at 50 ft
This same signal crossing lies close to a residential area with the following operating conditions:

Nd = 200 /15 hours = 13.3 events per hour
Nn =12 /9 hours = 1.33 events per hour
Calculate the daytime and nighttime Leglih,) at 50 ft.
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Cont.
25 Ldcross = 109 + 10109(13.3) + 101og(3600 ) — 35.6
= 63.1 dBA at 50 ft
25 = 109 + 10log(1.33) + 10log(3600) — 35.6
= 53.1 dBA at 50 ft
Calculate Ld. at 50 ft.
�dCross (LttCross+10) \
Ldn = 101.99(15 x 10� �1O� + 9 X 10� X10)) — 13.8
= 63.1 dBA at 50 ft
Note: Computation results should always be rounded to the nearest decibel at the end of the computation. In all examples of this section, however, the first decimal place is retained for readers to precisely match their own computations against the example computations.

Step 3: Determine Propagation Characteristics
Determine the combined propagation characteristics between each source and receiver of interest.
3a. Calculate project noise exposure as a function of distance. Calculate the project noise exposure at distances other than 50 ft, such as at receiver locations, as a function of distance accounting for shielding and ground effects along the path. See Example 4-8 below.

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1. Determine the topography of the ground within the transit corridor using the figures in Table 4-26 as a guide. It is not necessary to represent the transit corridor with an extreme number of changes in topography. Often, several typical sections will suffice throughout the transit corridor.

2. Use the equations in Table 4-26 to determine ground factor (G) based on the effective path height (Heft) for each identified terrain feature. Standard source heights are included at the bottom of the table. Assume receiver heights of 5 ft for both outdoor receivers and first -floor receivers. Note that larger ground factors correspond to larger amounts of ground attenuation with increasing distance from the source. For acoustically "hard" (e.g., non -absorptive) ground conditions, G should be taken to be zero.

3. Determine the distance correction factor using the ground factor and another distance, such as the distance to a receiver, and the equations in Table 4-27.

4. Apply the distance correction (Cd,,ta"ce) to the project noise exposure at 50 ft (Section 4.5, Step 2) using the following equation:

Ldistance
Lsoft
Ldistance = Lsoft + Cdistance
where:
= Ldn or LAeq(1hr) at the new distance, ft
= Ldn or LAeq(ihr) at 50 ft

5. Plot noise exposure as a function of distance if desired.

Eq. 4-42
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Table 4-26 Ground Factor G, for Ground Attenuation
Ground Factor
Soft Ground: 0.66,
Heff ≤ 5
G = 0.75(1 — H 2f ), 5
Figure 4-13 Source in Shallow Cut 2
-4--A-I.

B-41
,
H,s+4 He+Hr
H for Hr,≤He
•ili
eff 2
H
H
He _ HS+2H6—He+H
>H
H for
eff 2 c
Figure 4-14 Elevated Receiver
B
•)I)
Hb
f
:....j
TII'u'
B
Use Eq. 4-44 for A ≤
2 H4
y
He .

HS+2H6+He+Hr B
I. -A-..

Figure 4-15 Source in
Heff = 2 for A > 2
Sloped Cut
® .-
• —}
Hs + H,. B
He!! = A 5-2
H • 111
PHA 2 for
II, +2He+fl, B
A�
Heff= 2 for A>z
Figure 4-16 Source and Receiver Separated by Trench
H3 = 8 ft for trains with diesel-electric locomotives = 3 ft for 2 -axle city buses = 2 ft for trains without diesel-electric locomotives = 8 ft for 3 -axle commuter buses = 0 ft for automobiles
Note: Equations for He remain valid when Hb = 0
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Table 4-27 Distance Correction Factor Equations for Detailed Noise Analysis Source
Equation*
Stationary Sources
Cdistance =—201og(� ) — 10Glog(� )
50 50
Eq. 4-45
Fixed -guideway rail car passbys
Cdistance =—101og(D) — 10Glog(-)
50 42
Eq. 4-46
Fixed -guideway locomotive and rubber -
tired vehicle passbys, highway vehicle
passbys and horns
Cdistance =—101og(D ) — 1OGlog(�)
50 29
Eq. 4-47
D = distance, ft
G = ground factor, see Table 4-26
*These equations assume the distance between the source and receiver is approximately 300 ft or less. At longer distances, ground effects have an upper limit and atmospheric conditions may affect propagation characteristics. Therefore, more detailed calculation methods may be required to account for those effects.

Example 4-8: Detailed Noise Analysis — Exposure vs. Distance Curve Exposure vs. Distance Curve for Fixed -Guideway Source
Plot an exposure vs. distance curve for a diesel-electric commuter train that does not sound the horn in this area.

Assumptions
The terrain is flat grassland without a noise barrier.

Leg Loco (8 — 9am) = 72 dBA at 50 ft
Ldn.Loco = 68 dBA at 50 ft
Hr =5ft
Hb = 0 ft (for a "no noise barrier" case)
H, = 8 ft (for a diesel-electric commuter train)
Calculate Heff using the equations in Table 4-26.

HS + 2Hb + Hr
Heff —
2 8+0+5
2 = 6.5 ft
Determine the ground factor using Eq. 4-43.

G =0.75(1— H4eff)
= 0.63
Use Eq. 4-45 to determine noise vs. exposure equations for Labro and Leq.Loco = 72 — 101og(°) — 6.3Iog(°)
so az
Ldn.Loco
= 68 — 101og(s°—o) — 6.3Iog(42)
Plot the two equations (see example in Figure 4-17). From these curves, the noise levels due to this train operation can be determined for a receiver of interest at any distance without shielding.

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100 200 300
Distance D, ft
500
1,000
Figure 4-17 Example Exposure vs. Distance Curves
3b. Calculate the attenuation due to shielding for each distance of interest from Step 3a, using the following equation and Tables 4-26 through 4-30 and as illustrated in Example 4-9. If the conditions described in the tables are not met, the attenuation due to shielding is considered zero. Shielding can be due to intervening noise barriers, terrain features, rows of buildings, and dense tree zones.

Ashielding — max{/Lbarrier or Abuildings or Atreesl
where:

Ibarrier = barrier insertion loss, see Table 4-28
Abuildings
A trees
= attenuation due to buildings, see Table 4-29
= attenuation due to trees, see Table 4-30
Table 4-28 Barrier Insertion Loss
Eq. 4-48
Barrier
Insertion
Loss
D
!barrier = max{0 or (Abarrier - 10(GNB — GB) log( )))}
Eq. 4-49
A barrier
P
D
GNB
GB
= min{12 or [5.3 log(P) + 6.71}
For non -absorptive transit barriers within 5 ft of the rail = min{15 or (5.3 log(P) + 9.7)} For absorptive transit barriers within 5 ft of the rail

2.511/T For all other barriers, and for protrusion of terrain = min{15or(20log( ) + 5)}
tank (4.46vP)
above the line of sight
= path length difference, ft (see figure 4- I 8)*
= closest distance between the receiver and the source, ft = ground factor G computed without barrier (see Table 4-26) = ground factor G computed with barrier (see Table 4-26) * If the source height (exhaust outlet) for diesel-electric locomotives is not available, assume I5 ft.

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Barrier Parameter P
P= A -B -C
g Receiver
Ground
Barrier
Figure 4-I8 Noise Barrier Parameter "P"
Table 4-29 Attenuation due to Buildings
Condition
Equation
Gaps in the row of buildings constitute less
than 35% of the length of the row
Abuildings = min{10 or [1.5 (R — 1) + 5]}
Eq. 4-50
Gaps in the row of buildings constitute 35 to
65% of the length of the row
Abuadings = min{10 or [1.5 (R — 1) + 3])
Eq. 4-5

Gaps in the row of buildings constitute more
than 65% of the length of the row
Abuiidings = 0
R = number of rows of houses that intervene between the source and receiver Table 4-30 Attenuation due to Trees
Condition
Equation
At least 100 ft of trees intervene between the
source and receiver with no clear line -of -sight
between source and receiver, and the trees
extend 15 ft or more above the line -of -sight
( W
A„„, = min j 10 or 20} where W ≥ 100 f t
t J
= 0 where W < 100 f t
Eq. 4-52
W = width of tree zone along the line -of -site between the source and receiver in feet Example 4-9: Detailed Noise Analysis — Shielding
Computation of Shielding
The following features are between the rail corridor and a receiver of interest. Calculate the attenuation due to shielding.

1. A 15 -foot high noise barrier is 40 ft from the closest track and 130 ft from the receiver

2. A dense tree zone 100 ft thick that extends 15 ft above the line -of -sight Assumptions
H, =8ft
Hr =5ft
Barrier dimensions
A = 40.61 ft
B = 130.38 ft
C = 170.03 ft
Barrier
Calculate Herr with and without the barrier using the equations in Table 4-26.

Hs+2Hb+Hr
Heff.NoBarrier =
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8+0+5
2 = 6.5 ft
Heff.Barrier
H5 + 2Hb + Hr
2 8+15+5
2 = 21.5 ft
Determine the ground factor with and without the barrier using Eq. 4-43.

Heff
GNOBarrier = 0.75(1 - 42 )
= 0.63
He"f
GBarrier = 0.75(1— 42 )
= 0.37
Calculate the barrier insertion loss using Table 4-28 and Figure 4-18.

P =A+B-C
= 0.96 ft

2.511(P
Abarrier = min{15or(20log( ) + 5))
tanh(4.46.TP)
}Lbarrier
= 12.8 dB
= min { 15 or 12.8)
= 12.8 dB
01-31
Cont.
/ D
= max{0 or (Abarrier - 10(GNOBarrier — GBarrier) log(50))) 170
= 12.8 - 10(0.63 - 0.37) log( 50 )
=11.4dB
Trees
Determine the attenuation due to trees using Table 4-30.

W
Atrees = mitt{10 or 20}
= 5 dB
Total Shielding
The total shielding is the maximum of the barrier and tree zone shielding, 11.4 dB.

Ashieiding = maxt/Lb,i, or Abuiidings or Atrees}
= max{11.4 or 0 or 5}
= 11.4 dB
Note: Computation results should always be rounded to the nearest decibel at the end of the computation. In all examples of this section, however, the first decimal place is retained for readers to precisely match their own computations against the example computations.

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3c. Combine the two propagation characteristics.

Combine the results from Steps 3a and 3b to determine the noise at the receiver considering the propagation characteristics of distance and shielding by applying the distance correction and attenuation due to shielding to the project noise exposure level at 50 ft.

The equations in Table 4-31 combine the equations in Steps 3a and 3b.

Table 4-3I Calculate Ld. or Leq(inr)
Source
Equation*
Stationary Sources
LDistshield = L 201og(�50 ) — 10G1og(�50 ) Ashielding
Eq. 4-53
Fixed -guideway rail car
passbys
D D
LDistshield = L — 101og(50) - 10Glog(42) — Ashielding
Eq. 4-54

Fixed -guideway locomotive
and rubber -tired vehicle
passbys, highway vehicle
passbys and horns
L L 1010 D lOG(o D A
DistShield g(SO) 9(29) shielding
Eq. 4-55
L = Lan or Leq
D = distance, ft
G = ground factor, see Section 4.5, Step 3a
Ashielding = attenuation due to shielding, see Section 4.5, Step 3b. *These equations assume the distance between the source and receiver is approximately 300 ft or less. At longer distances, ground effects have an upper limit and atmospheric conditions may affect propagation characteristics.

Therefore, more detailed calculation methods may be required to account for those effects.(2a. 29) Step 4: Combine Noise Exposure from All Sources
Combine all sources to predict the total project noise at the receivers using the equations in Table 4-32 after propagation adjustments have been made for the noise exposure from each source separately.

Table 4-32 Computing Total Noise Exposure
Total 1 -who from all sources
for the hour of interest:

LAeq(1hr)/1l)
Leq.total(ihr) = 101og(-all sources 10 )
Eq. 4-56
Total Ld„ from all sources
Ldn.total = 101og(Eau sources 10Ldn/10)
Eq. 4-57
Example 4-10 Detailed Noise Analysis — Combine Sources
Computation of Total Exposure from Combined Sources
Combine the noise exposure from the commuter train and light rail system to estimate the total noise exposure at the receiver.

Assumptions
A commuter train operation produces the following levels at a receiver of interest:

Leq.commuter = 72 dBA
Ldn.commuter = 68 dBA
A light rail system produces the following levels at the same receiver:

Leq.LightRait = 69 dBA
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Ldn.LightRail = 70 dBA
No other project sources affect this receiver.

Calculate the total noise exposure at the receiver using the equations in Table 4-32.

Leq.totai
Ldn.total
= 10log(10(72/10) + 10(69/1°))
= 73.8 dBA
= 10log(10(68/10) + 10(70/10))
= 72.1 dBA
Note: Computation results should always be rounded to the nearest decibel at the end of the computation. In all examples of this section, however, the first decimal place is retained for readers to precisely match their own computations against the example computations.

Step 5: Determine Existing Noise Exposure
Choose the appropriate method for characterizing noise and then determine the existing noise at each identified noise -sensitive receiver. The existing noise is needed to determine the noise impact according to the criteria described in Section 4.1, Step 2. Recall that impact is assessed based on a comparison of the existing ambient noise exposure and the additional noise exposure that will be caused by the project. The existing noise exposure must be estimated for all receivers of interest identified in Section 4.5, Step I.

For a Detailed Noise Analysis, it is recommended to measure existing noise at each receiver of interest identified in Section 4.5, Step I, for the most precise assessment of existing noise and conclusions concerning noise impact. However, measurements are expensive, often thwarted by weather, and take considerable time in the field. If taking measurements at each identified receiver is not possible, other less precise methods are available. Different methods may be used at different receivers along the project. However, it is important to recognize the correlation between the precision of measurements and the confidence in the impact assessment. Especially in a Detailed Noise Analysis, avoid using less precise methods of measuring existing noise just for the sake of convenience or expediency. The use of less precise methods must be clearly justified.

Option A. Noise Exposure Measurements — Full one -hour measurements are the most appropriate way to determine ambient noise exposure for non-residential receivers with the level of precision expected in a Detailed Noise Analysis. For residential receivers, full 24 -hour measurements are more appropriate. These full -duration measurements are preferred over other methods of characterizing existing noise where time and study funds allow.

Follow the procedures below for these full -duration ambient noise exposure measurements:

Ai. Non-residential land uses — Measure a full hour Lego hr) at the receiver of interest on at least two non -successive weekdays (generally between noon on Monday and noon on Friday). Select the hour of the day when the maximum project activity is expected to occur.

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A.ii. Residential land uses — Measure a full 24 -hour Lan at the receiver of interest for a single weekday (generally between noon on Monday and noon on Friday).

A.iii. Microphone position — The location of the microphone at the receiver depends upon the proposed location of the transit noise source, so use good technical judgment in positioning the measurement microphone. If, for example, a new rail line will be in front of the house, do not locate the microphone in the backyard behind the house where the line of sight between the noise source and receiver is obstructed. Figure 4-19 illustrates recommended measurement positions for various locations of the project, with respect to the house and the existing source of ambient noise.

A.iv. Measurement guidelines — Undertake all measurements in accordance with good engineering practice following guidelines given in ASTM and ANSI standard s.(3o)(3I)
I I I I I ! 1 I Y
1 1 1 Project Source
Amhien4 Source
• or • or •
House
I
Offset: 6 to 10 ft
Ambient Source
I
Project Source
•
I I i
or • or
I I 1 1 l i I I I I 1 1 1
•
House
Offset- 6 tit or More
I
I t I Project Source
House
-f—
setl 6 le 10 ft
On Centerline
-
Ambient Source
I i I I 1 1 1 I 1 I 1 1 1 I 1 1 1 1
Flj
Project Source
-/ Predict Project Noise
+
g
iit �
Measure Ambient Noise
..

E
a
Offset: 8 to 10 0
On Centerline
• = Microphone Location
Figure 4-I9 Recommended Microphone Locations
for Existing Noise Measurements
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Option B. Noise Exposure Computations from Partial Measurements — Often, measurements can be made at some of the receivers of interest and used to estimate noise exposure at nearby receivers. In other situations, several Leg( Ihr) measurements can be taken at a receiver and then the Lan computed from these. Both options require experience and knowledge of acoustics to select representative measurement sites. If using this method to compute an Ldn, a minimum time period of one hour should be used for each measurement period. It is unacceptable to extrapolate a one hour measurement from a shorter measurement period.

Measurements at one receiver can be used to represent the noise environment at other sites, but only when proximity to major noise sources is similar among the sites. Residential neighborhoods with otherwise similar homes may have greatly varying noise environments. For example, one area of the neighborhood may be located where the ambient noise is clearly due to highway traffic. A second area toward the interior of the neighborhood may have highway noise as a factor, but also include other noise sources from the community. A third area located deep into the residential area could have local street traffic and other community activities dominate the ambient noise. In this example, three or more measurement sites would be required to represent the varying ambient noise conditions in a single neighborhood.

Typical situations where representative measurement sites can be used to estimate noise levels at other sites occur when both share the following characteristics:
• Proximity to the same major transportation noise sources, such as highways, rail lines and aircraft flight patterns
• Proximity to the same major stationary noise sources, such as power plants, industrial facilities, rail yards and airports
• Similar type and density of housing, such as single-family homes on quarter -acre lots and multi -family housing in apartment complexes Acoustical professionals are often adept at such computations from partial data and are encouraged to use their experience and judgment in fully utilizing the measurements in their computations. This does necessitate a conservative estimate (underestimate) of existing noise to account for reduced precision from partial data as compared to full noise measurements.

Those without a background in acoustics are encouraged to use the procedures in Appendix E to compute existing noise from partial measurements. These methods include a factor to conservatively estimate (underestimate) existing noise to account for reduced precision from partial data as compared to full noise measurements.

Option C. Estimating Existing Noise Exposure — The least precise way to determine noise exposure is to estimate it from a table. This method is often used for the General Noise Assessment, but it is not recommended for a Detailed Noise Analysis. It can be used, however, in the absence of better data for locations where roadways or railroads are the predominant ambient noise source. Table 4-17 presents these existing levels. The levels in Table 4-17 are FEDERAL TRANSIT ADMINISTRATION 94
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conservative and underestimate existing noise to account for reduced precision compared to full noise measurements. If a simplified procedure to estimate existing noise exposure is chosen it must be clearly justified and receive approval by the FTA Regional office.

While measurements are considered the most precise method, there is one situation where it may be more accurate to estimate rather than measure the existing noise exposure, which is in areas near major airports where aircraft noise is dominant. Because airport noise is highly variable based on weather conditions and corresponding runway usage, it is preferable in such cases to base the existing noise exposure on published aircraft noise contours in terms of Annual Average Ld,,.

Step 6: Assess Noise Impact
Assess noise impact at each receiver of interest identified in Section 4.5, Step I using the noise impact criteria in Section 4.1 and the procedures in this step.

Choose the appropriate noise impact assessment procedure for a transit project or multimodal project.

Option A. Transit Projects — For transit projects, noise impact is assessed at each receiver of interest using the criteria for transit projects described in Section 4. I. The noise impact assessment procedure is as follows:

A.i. Tabulate existing ambient noise exposure (rounded to the nearest whole decibel) at all receivers identified Section 4.5, Step I. In cases where large residential buildings are exposed to noise on one side only, the receivers on that side are included in the analysis.

A.ii. Tabulate project noise exposure at these receivers from Section 4.5, Step 4.

A.iii. Determine the level of noise impact (no impact, moderate impact, or severe impact) according to Section 4. I .

A.iv. Document the results in noise -assessment inventory tables. Include the following information:
• Receiver identification and location
■ Land use description
■ Number of noise -sensitive sites represented (number of dwelling units in residences or acres of outdoor noise -sensitive land) • Closest distance to the project
• Existing noise exposure
• Project noise exposure
• Level of noise impact (no impact, moderate impact, or severe impact) • A sum of the total number of receivers and numbers of dwelling units predicted to experience moderate impact or severe impact A.v. Illustrate the areas of moderate impact and severe impact. Two methods of displaying impact are labeling and contouring.

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In a Detailed Noise Analysis, the most accurate indication of impact is to label each impacted building or cluster identified in the inventory table.
• A less precise illustration of impacted areas is a plot of project noise contours on the maps or aerial photographs, along with shaded impact areas. Use the procedures in Section 4.4, Step 6 and the levels from Section 4.5, Step 2 to develop these contours.

Note that it is difficult to position noise contours in urban areas due to shielding, terrain features, and other propagation anomalies. If noise contours are used, they should be considered illustrative rather than definitive. If desired to conform to the practices of another agency, the contouring may perhaps include several contour lines of constant project noise, such as Ldr, 65, Ldn 70, and Ldn 75 dBA.

A.vi. Including information on the magnitude of the impacts is an essential part of the assessment. The magnitude of noise impact is defined by the two threshold curves delineating onset of moderate impact and severe impact.

Option B. Multimodal Projects — For multimodal projects, project noise comprised of both highway and transit noise sources that are assessed according to the FTA noise impact criteria (see Table 4-2), use the procedure in Option A above. For multimodal projects that require FHWA's noise assessment methods to inform FTA's evaluation (see Section 4.1, Step I - Option B), follow the FHWA guidance.(32) In general, the appropriate calculation method is to use the current version of FHWA's Traffic Noise Model (TNM).(22) TNM is a state-of-the-art computer program used for predicting noise impacts near highways.

TNM allows for a detailed assessment at each receiver of interest by separately calculating the noise contribution of each roadway segment. For each roadway segment, the noise from each vehicle type is computed from reference noise levels, adjusted for:
■ Vehicle volume
■ Vehicle speed
• Grade
• Roadway segment length
• Source -to -receiver distance
Further adjustments needed to accurately model the sound propagation from source to receiver include:
• Shielding provided by rows of buildings,
■ Effects of different ground types,
■ Source and receiver elevations, and
• Effect of any intervening noise barriers.

TNM sums the noise contributions of each vehicle type for a given roadway segment at the receiver. TNM then repeats this process for all roadway segments, summing their contributions to generate the predicted noise level at each receiver.

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Step 7: Determine Noise Mitigation Measures
Evaluate alternative mitigation measures where the Detailed Noise Analysis shows either severe or moderate impact, and it is not feasible to change the alignment or location of the project to avoid impact. Project noise that is found to cause no impact does not generally require any mitigation.

Mitigation of noise impact from transit projects may involve treatments at the three fundamental components of the noise problem: at the noise source, along the source -to -receiver propagation path, or at the receiver. Generally, the transit property has authority to treat the source and some elements of the propagation path, but may have little or no authority to modify anything at the receiver. After mitigation options have been determined, repeat the project noise computations including the adopted mitigation and reassess the remaining noise impact.

Approximate costs for noise control measures are documented in a report from the Transit Cooperative Research Program (TCRP)(33) and are also presented in this section. These costs reflect the noise mitigation costs available in 1997 (unless otherwise noted), which are the most recent data available as of this publication, 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.
7a. Evaluate Source Treatments — The most effective noise mitigation treatments are applied at the noise source. This is the preferred approach to mitigation when possible. Common source treatments and their estimated acoustical effectiveness are included in Table 4-33 and described below. It is important to note that the values below are estimates and should be applied with good engineering judgement. It also important to note that these mitigation measures should not be applied as a reduction in the reference SEL values for a vehicle that already incorporates that measure as a feature, such as vehicle skirts. Measurements to determine the reference SEL source level are required in those instances.

Table 4-33 Transit Noise Mitigation Measures — Source Treatments Mitigation Measure
Effectiveness
Stringent Vehicle & Equipment Noise Specifications
Varied
Operational Restrictionst
Varied
Resilient Damped Wheels* I For rolling noise on tangent track:
2 dB
or
I For wheel squeal on curved track:
10-20 dB
Vehicle Skirts*
6-10 dB
Undercar Absorption*
5 dB
Quiet Fan Design and Fan Placement*
Varied
Preventative Maintenance on Rail Systems*
Varied
Resurfacing Roads**
10 dB
Guideway Support for Buses**
I 0 dB
Turn Radii Greater than 1000 ft*
Avoids Squeal
Rail Lubrication on Sharp Curves*
Reduces Squeal
Movable -Point Frogs (reduce rail gaps at crossovers)*
Reduces Impact Noise
Engine Compartment Treatments
6-10 dB
Quiet Zones*
Reduces occurrence of horn noise
tFTA does not normally accept operational restrictions as a noise mitigation measure — see below. * Applies to rail projects only.
** Applies to bus projects only.

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• Stringent Vehicle and Equipment Noise Specifications
▪ Vehicles — Among the most effective noise mitigation treatments is noise control during the specification and design of the transit vehicle.

Such source treatments apply to all transit modes. By developing and enforcing stringent but achievable noise specifications, the transit property takes a major step in controlling noise everywhere on the system. It is important to ensure that the noise levels quoted in the specifications are achievable with the application of best available technology during the development of the vehicle and reasonable considering the noise reduction benefits and costs.

Effective enforcement includes penalties for non-compliance with the specifications. The noise mitigation achieved by source treatment is dependent on the quality of installation and maintenance. Vehicles failing to meet the noise specification could result in complaints from the public and require additional noise mitigation measures applied along the path or at receivers.
▪ Stationary sources — Stringent but achievable noise specifications for stationary sources are also an effective approach for mitigating noise impacts. Typical equipment includes fixed plant equipment such as transformers and mechanical equipment, as well as grade -crossing signals. For example, it may be possible to reduce noise impact from grade -crossing signals in some areas by specifying equipment that sets the level of the warning signal lower in locations where ambient noise is lower to minimize the signal noise in the direction of noise -sensitive receivers.
■ Operational Restrictions — Changes in operations that can mitigate noise include the lowering of speed, the reduction of nighttime (10 p.m. to 7 a.m.) operations, and reduction of warning horns and signals. ▪ Speed reduction — Because noise from most transit vehicles is dependent on speed, a reduction of speed results in lower noise levels.

The effect can be considerable. For example, the speed dependency of steel-wheel/steel-rail systems for Leglinr) and Ldr, (Table 4-21) results in a 6 -dB reduction when reducing the speed to half of the original speed.

Although there are tangible benefits from speed reductions during the most noise -sensitive time periods, FTA does not ordinarily accept speed reduction as a noise mitigation measure for two important reasons:
speed reduction is unenforceable and negated if vehicle operators do not adhere to established policies, and 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.
▪ Reduction of nighttime operations — Complete elimination of nighttime operations has a strong effect on reducing the Ldn, because nighttime noise is increased by 10 dB when calculating Ld,,. But restrictions on operations are usually not feasible because of service demands. FTA generally does not pursue restrictions on operations as a FEDERAL TRANSIT ADMINISTRATION 98
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noise reduction measure. However, if early morning idling can be curtailed to the minimum necessary, however, this can have a measurable effect on Ld,,.

While there are tangible benefits from limits on operations during the most noise -sensitive time periods, FTA does not recommend limits on operations as a way to reduce noise impacts because 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. • Reduction of warning horns and signals — Minimizing or eliminating horns and other warning signals at gate crossings can reduce noise impact for light rail and commuter rail systems. Although these mitigation options are limited by safety considerations, they can be effective in the right circumstances. For examples, see quiet zones below and wayside horns in Step 7b.
■ Wheel Treatments (Rail) — A major source of noise from steel -wheel and steel -rail systems is the wheel/rail interaction that can produce three distinctive sounds: roar, impact, and squeal (as discussed in Section 3.2).

Roar is the rolling noise caused by small-scale roughness on the wheel tread and rail running surface. Impacts are caused by discontinuities in the running surface of the rail or by a flat spot on the wheels. Squeal occurs when a steel -wheel tread or its flange rubs across the rail, resulting in resonant vibrations in the wheel that creates a screeching sound. Various wheel designs and other mitigation measures exist to reduce the noise from each of these three mechanisms.
• Resilient wheels — Resilient wheels are effective in eliminating wheel squeal on tight turns with reductions of I O to 20 dB in the high - frequency range where squeal noise occurs. Rolling noise is also slightly reduced with resilient wheels and typically achieves a 2 -dB reduction on tangent track. The costs for resilient wheels are approximately $2000 to $3000 per wheel, as compared to about $400 to $700 for standard steel wheels.(vi)
• Damped wheels — Damped wheels, like resilient wheels, are effective in eliminating wheel squeal on tight turns with reductions of 5 to 15 dB in the high -frequency range where squeal occurs. Rolling noise is also slightly reduced by approximately 2 dB on tangent track. This treatment involves attaching vibration absorbers to standard steel wheels. The costs for damped wheels add approximately $500 to $1000 to the normal $700 for each steel wheel.
vi Assumes 8 wheels per vehicle.

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• Vehicle Treatments — Vehicle noise mitigation measures are applied to the various mechanical systems associated with propulsion, ventilation, and passenger comfort. Propulsion systems of transit vehicles include diesel engines, electric motors, and diesel-electric combinations. Noise from the propulsion system depends on the type of unit and how much noise mitigation is built into the design. Mufflers on diesel engines are generally required to meet noise specifications; however, mufflers are generally practical only on buses, not on locomotives. Control of noise from engine casings may require shielding the engine by body panels without louvers, dictating other means of cooling, and ventilation.

Ventilation requirements for vehicle systems are related to the noise generated by a vehicle. Fan noise often remains a major noise source after other mitigation measures have been instituted because of the need to have direct access to cooling air. This applies to heat exchangers for electric traction motors, diesel engines, and air-conditioning systems. The mitigation options for these systems include:
o Quiet fan design and placement — Fan noise can be reduced by installation of quiet, efficient fans. Forced -air cooling on electric traction motors can be quieter than self -cooled motors at operating speeds.

Placement of fans on the vehicle can make a considerable difference in the noise radiated to the wayside or to patrons on the station platforms.
• Vehicle skirts and undercar absorption — The vehicle body design can provide shielding and absorption of the noise generated by the vehicle components. Acoustical absorption under the car has been demonstrated to provide up to 5 dB of mitigation for wheel/rail noise and propulsion -system noise on rapid transit trains. Similarly, vehicle skirts over the wheels can provide more than 5 dB of mitigation. By carrying their own noise barriers, vehicles with these features can provide cost-effective noise reduction. The cost for vehicle skirts will add approximately $5000 to $10000 per vehicle. Undercar absorption will add approximately $3500 per vehicle, assuming that 50% of the underside of the floor is treated.
• Preventative Maintenance (Rail) — Preventative maintenance is the best strategy to minimize rail and wheel deterioration. 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 noise and vibration in systems with deferred maintenance. This can be accompanied by considerable life cost benefits for the transit system. • Spin -slide control systems — Similar to anti -locking brake systems (ABS) on automobiles, spin -slide control systems reduce the incidence of wheel flats, a major contributor of impact noise. Trains with smooth wheel treads can be up to 20 dB quieter than those with wheel flats. To be effective, the anti -locking feature should be in operation during all braking phases, including emergency braking. Wheel flats are more likely FEDERAL TRANSIT ADMINISTRATION 100
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to occur during emergency braking than during dynamic braking. The cost of slip -slide control may be incorporated in the new vehicle costs, but may be between $5,000 and $10,000 per vehicle with a maintenance cost of $200 per year.

Wheel truing — Maintenance of wheels by truing eliminates wheel flats from the treads and restores the wheel profile. As discussed above, wheel flats are a major source of impact noise. As a guideline, it is recommended that wheel sets match within approximately ±0.0I inch and all wheels on the same truck should match within ±0.02 inches to minimize damage and wear to wheels and rails.(34) A wheel truing machine costs approximately $ I million, including associated maintenance materials and labor costs. The TCRP report estimates a system with 700 vehicles would incur a yearly cost of $300,000 to $400,000 for a wheel truing program.

It is recommended to install wheel -flat detector systems to identify vehicles that are most in need of wheel truing. These systems are becoming more common on railroads and intercity passenger systems, but are relatively rare on transit systems.

Rail grinding — The smoothness of the running surface is critical in the mitigation of noise from a moving vehicle. Mill scale grinding before commencement of pre -revenue service train operations is critical.

Experience shows that grinding new rails after approximately 3 months of train operations and scheduling routine grinding at approximate intervals of 2 years in the problem areas would minimize noise problems related to corrugation in most cases. Grinding with small machines when the corrugation depth is still small is a reasonable approach. As a guideline, it is recommended to spot -grind at locations where corrugation occurs before corrugation grows to 0.02 inches (32).

Periodic rail grinding can result 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 of approximately $1 million for the equipment and do their own grinding. Contractors typically charge a fixed amount per day for the equipment on site, plus an amount per pass -mile (one pass of the grinding machine for one mile).

Typical rail grinding cost would be approximately $7,000 to $ 10,000 per pass -mile.

Wheel and rail profile matching — It is important to consider the wheel and rail profile compatibility when truing wheels and grinding rails. If the profiles do not match, the benefits of this kind of preventative maintenance will not be achieved.

It is equally important to consider initial wheel and rail profile compatibility. Work with track designers and vehicle suppliers early in the design process to ensure wheel and rail profile compatibility.

Profiles should be defined during the design phase and should be in FEDERAL TRANSIT ADMINISTRATION 101
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place when system opens.(32) The cost of wheel and rail profile matching may be incorporated in the new vehicle and new rail costs.

Profile grinding of the rail head in combination with a wheel truing program may be the most practical approach to controlling and reducing noise and vibration where such practices are not normally conducted.
• Maintenance program — Clearly defined maintenance specifications should be developed during design phase of the project. The specifications should define rail and wheel profiles, include detailed guidance for pre -revenue mill scale grinding, address issues related to healthy rail -wheel interface, and include a mechanism for periodic monitoring of wheel and rail condition and verification for compliance.(32) A diligent maintenance program can often resolve or reduce rail noise issues before they occur. Vehicle reconditioning programs should also be developed particularly for components such as suspension system, brakes, wheels, and slip -slide detectors. • Guideway Support (Bus) — The smoothness of the running surface is critical in the mitigation of noise from a moving vehicle. ▪ Resurfacing roads — Roughness on the guideway can be eliminated by resurfacing roads, thereby reducing noise levels by up to 10 dB. • Bridge expansion joint angles and design — Bridge expansion joints are also a source of noise for rubber -tire vehicles. This source of noise can be reduced by placing expansion joints on an angle or by specifying the serrated type rather than joints with right-angle edges. • Turn Radii and Rail Lubrication — For steel-wheel/steel-rail systems with non-steerable trucks and sharp turns, squeal can typically be eliminated by designing all turn radii to be greater than 1000 ft, or 100 times the truck wheelbase, whichever is less. If this is not possible, squeal can be mitigated by installation of lubricators (though the potential environmental impacts of lubricant application should be factored into this decision).Rail lubricators cost approximately $10,000 - $40,000 per curve.
• Movable -point and Spring -rail Frogs — Frogs with spring -loaded mechanisms and frogs with movable points can reduce impact noise near crossovers. According to the TCRP report, a spring frog costs approximately $12,000, twice the cost of a standard frog. A movable point frog involves elaborate signal and control circuitry resulting in higher costs of approximately $200,000.
• Use of Locomotive Horns at -grade Crossings and Quiet Zones — In cases where commuter rail operations share tracks or ROW with freight or intercity passenger trains that are part of the general railroad system, the safety rules of the FRA, including the Train Horn Rule, apply.(35) The Train Horn Rule requires that locomotive horns be sounded at public highway grade crossings, although some exceptions are allowed in carefully defined circumstances. Locomotive horns are often a major contributor in FEDERAL TRANSIT ADMINISTRATION 102
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projections of adverse noise impact, in the community from proposed commuter rail projects. Since noise barriers are not feasible at highway -rail grade crossings, the establishment of quiet zones could be considered.

Quiet zones can be established in which supplemental safety measures (SSMs) are used in place of the locomotive horn to provide an equivalent level of safety at -grade crossings.(vii) By adopting an approved SSM at each public grade crossing, a quiet zone of at least a half -mile long can be established. These measures are in addition to the standard safety devices required at most public grade crossings (e.g., stop signs, reflectorized crossbucks, flashing lights with gates that do not completely block travel over the tracks). Below are four SSMs that have been predetermined by the FRA to fully compensate for the lack of a locomotive horn:
▪ Temporary closure of a public highway -rail grade crossing — This measure requires closure of the grade crossing for one period each 24 hours, and the closure must occur at the same time each day. ▪ Four -quadrant gate system — This measure involves the installation of at least one gate for each direction of traffic to fully block vehicles from entering the crossing.

Gates with medians or channelization devices — This measure keeps traffic in the proper travel lanes as it approaches the crossing.

This denies the driver the option of circumventing the gates by traveling in the opposing lane.
▪ One-way street with gates — This measure consists of one-way streets with gates installed, so that all approaching travel lanes are completely blocked.

In addition to the pre -approved SSMs, the FRA rule also identifies a range of other measures that may be used in establishing a quiet zone. These could include modified SSMs or non -engineering types of measures, such as increased monitoring by law enforcement for grade crossing violations or instituting public education and awareness programs that emphasize the risks associated with grade crossings and applicable requirements. These alternative safety measures (ASMs) require approval by FRA based on a demonstration that public safety would not be compromised by eliminating horn usage.

The lead agency for designating a quiet zone is the local public authority responsible for traffic control and law enforcement on the roads crossing the tracks. To satisfy the FRA regulatory requirements, the public transit agency must work closely with this agency while also coordinating with any freight or passenger railroad operator sharing the ROW. The final environmental document should discuss the main considerations in adopting the quiet zone including: the engineering feasibility, receptiveness of the local public authority, consultation with the railroad, preliminary cost estimates, and evidence of the planning and interagency coordination that has occurred to date. If a quiet zone will be relied on as a mitigation measure, the final environmental document should provide reasonable vh For more information on quiet zones, visit: https://www.fra.dot.gov/Page/P0889 .

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assurance that any remaining issues can and will be resolved. For more information on documentation requirements see Section 8.

The cost of establishing a quiet zone varies considerably, depending on the number of intersections that must be treated and the specific SSMs, ASMs, or combination of measures that are used. The FRA gives a cost estimate of $ 15,000 per crossing for installing two 100 -foot -long, non -traversable medians that prevent motorists from driving around closed gates. A typical installation of a four -quadrant gate system is in the range of $ I 75,000- $300,000 per crossing.(36) Who pays for the installation of modifications can become a major consideration in a decision to pursue a quiet zone designation, especially in cases where noise from preexisting railroad operations is controversial in the community. In many cases where a quiet zone would mitigate a severe impact caused by the proposed transit project, the costs are covered by the project sponsor and FTA in the same proportion as the overall cost -sharing for the project. 7b. Evaluate Path Treatments — When noise mitigation treatments cannot be applied at the noise source or additional mitigation is required after treating the source, the next preferred placement of noise mitigation is along the noise propagation path between the source and receiver. Common path treatments and their estimated acoustical effectiveness are included in Table 4-34 and described below.

Table 4-34 Transit Noise Mitigation Measures — Path Treatments Mitigation Measure
Effectiveness
Noise barriers close to vehicles
6-15 dB
Noise barriers at row line
3-15 dBi3 I
Alteration of horizontal & vertical alignments
Varied
Wayside horns
Varied
Acquisition of buffer zones
Varied
Ballast on at -grade guideway*
3 dB
Ballast on aerial guideway*
5 dB
Resilient track support on aerial guideway
Varied
Vegetation and trees
Varied, see Table 4-30
* Applies to rail projects only.
• Noise Barriers — Noise barriers are effective in mitigating noise when they break the line -of -sight between source and receiver. The mechanism of sound shielding is described in Section 3.3. The necessary height of a barrier depends on the source height and the distance from the source to the barrier, see Table 4-28 and Figure 4- 18.
• Noise barriers close to vehicles — Barriers located very close to a rapid transit train, for example, may only need to be approximately 3 to 4 ft above the top of rail to be effective. Standard barriers close to vehicles can provide noise reductions of 6 to 10 dB.
• Noise barriers at ROW line — Barriers on the ROW line or for trains on the far track, the height must be increased to provide equivalent effectiveness to barriers located close to the vehicles.

Otherwise, the effectiveness can drop to 3 dB or less, even if the barrier breaks the line -of -sight.

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All barrier effectiveness can be increased by as much as 5 dB by applying sound -absorbing material to the inner surface of the barrier. The length of the barrier wall is also important to its effectiveness. The barrier must be long enough to block noise from a moving train along most of its visible path. This is necessary so that train noise from beyond the ends of the barrier will not severely compromise noise -barrier performance at noise - sensitive locations. The barrier length can be refined in the engineering phase, closely examining the predicted sound level exceedances at specific receivers, site geometries, and the contribution of barrier flanking noise, then adjusting the length as appropriate.

Noise barriers can be made of any outdoor weather -resistant solid material that meets the minimum sound transmission loss required by the project.

Materials that are commonly used for noise barriers include I 6 -gauge steel, I -inch thick plywood, and any reasonable thickness of concrete. Typically, a surface density of 4 pounds per square foot is required. Areas with strong winds may require more stringent structural requirements. It is critical to seal any gaps between barrier panels and between the barrier and the ground or elevated guideway deck for maximum performance.

Costs for noise barriers (based on highway installations) range from $20 to $25 per square foot of installed noise barrier at -grade with additional cost for design and inspection.(38) Installation on aerial structures could be twice the amount of installation at -grade, especially if the structure has to be strengthened to accommodate the added weight and wind load.

As described in Section 3.3, noise barriers, if not designed and sited carefully, can reduce visibility of trains for pedestrians and motorists, which causes safety concerns. It is important to consult with safety experts in choosing and siting a noise barrier.
• Alteration of Horizontal and Vertical Alignments — Transit alignment in a cut as part of grade separation can accomplish the same result as installation of a noise barrier at -grade or on aerial structure. The walls of the cut serve the same function as barrier walls in breaking the line -of -sight between source and receiver.
• Wayside Horns — The sounding of a locomotive horn as the train approaches an at -grade intersection produces a very wide noise footprint in the community. Using wayside horns at these intersections instead of the locomotive horn can substantially reduce the noise footprint without compromising safety at the grade crossing.

A wayside horn does not need to be as loud as a locomotive horn, and the warning sound is focused only on the area where it is needed. These are pole -mounted horns used in conjunction with flashing lights and gates at the intersection, with a separate horn oriented toward each direction of oncoming vehicle traffic. Noise levels in nearby residential and business areas can be reduced substantially with wayside horns, depending on the location with respect to the grade crossing.

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A plan to use wayside horns in place of the locomotive horn at public grade crossings must be coordinated with several public and private entities, notably the local agency having responsibility for traffic control and law enforcement on the road crossings, the state agency responsible for railroad safety, any railroads that share the ROW, and FRA. Public notification must also be given. Preliminary cost information from testing programs indicates a wayside horn system at a railroad/highway grade crossing costs approximately $50,000.
• Buffer Zones — Because noise levels attenuate with distance, one noise mitigation option is to increase the distance between noise sources and the closest noise -sensitive receivers. This can be accomplished by locating alignments away from noise -sensitive sites. Acquisition of land or purchasing easements for noise buffer zones is an option that may be considered if appropriate for the project.
■ Ground Absorption — Ballast on Guideways — Propagation of noise over ground is affected by whether the ground surface is absorptive or reflective. Noise from vehicles on the surface is strongly affected by the character of the ground in the immediate vicinity of the vehicle. Roads and streets for buses are hard and reflective, but the ground at the side of a road has a substantial effect on the propagation of noise to greater distance.

Guideways for rail systems can be either reflective or absorptive, depending on whether they are concrete or ballast. Ballast on a guideway can reduce train noise 3 dB at -grade and up to 5 dB on an aerial structure. • Vegetation and Trees — In almost all cases, vegetation and trees are ineffective at providing noise mitigation. Vegetation and Trees can provide some mitigation if at least 100 ft of trees intervene between the source and receiver, if no clear line -of -sight exists between the source and receiver, and if the trees extend I5 ft or more above the line -of -sight as described in Section 4.5, Step 3b. This is generally not a recommended form of mitigation to pursue.
7c. Evaluate Receiver Treatments — Consider treatments to the receivers when noise mitigation treatments cannot be applied at the source or along the propagation path, or if combinations of treatments are required. Common receiver treatments and their estimated acoustical effectiveness are included in Table 4-35 and are described in this section.

Table 4-35 Transit Noise Mitigation Measures — Receiver Treatments Mitigation Measure
Effectiveness
Acquisition of Property Rights for Construction of Noise Barriers 5-10 dB
Building Noise Insulation
5-20 dB
• Noise Barriers — In certain cases, it may be possible to acquire limited property rights for the construction of noise barriers at the receiver. As discussed above, barriers need to break the line -of -sight between the noise source and the receiver to be effective and are most effective when they are FEDERAL TRANSIT ADMINISTRATION 106
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closest to either the source or the receiver. See Section 3.3 for more information on noise barriers.
• Building Insulation — In cases where noise barriers are not feasible —such as multi -story buildings, buildings very close to the ROW, or grade crossings —the only practical noise mitigation measure may be to provide sound insulation for the buildings. In these cases, the need for mitigation at locations where impact has been identified will depend on the use (outdoor vs. indoor), any existing outdoor to indoor reduction in noise levels, and the feasibility of constructing effective noise barriers for second stories and above.

Depending on the quality of the original building facade, especially windows and doors, sound insulation treatments can improve the noise reductions from transit noise by 5 to 20 dB. To be considered cost-effective, a treatment should provide a minimum reduction of 5 dB in the interior of the building and meet the Ldr, 45 dBA interior criterion. For more information, see Section 4.1.

In many cases, especially in locations with high ambient noise levels, the existing sound insulation of a building may already meet the 45 dBA Ld„ interior noise criterion. It is recommended that sound insulation testing be conducted to determine if the existing sound insulation is sufficient or what additional measures would be required to meet the interior criterion.

Effective treatments include:
• Caulking and sealing gaps in the building facade; and Installation of new doors and windows that are specially designed to meet acoustical transmission -loss requirements:

Exterior doors facing the noise source should be replaced with well-gasketed, solid -core wood doors and well-gasketed storm doors.
- Acoustical windows are typically made of multiple layers of glass with air spaces between to provide noise reduction. Acoustical performance ratings are published in terms of Sound Transmission Class (STC) for these windows. It is recommended to use a minimum STC rating of 39 on any window exposed to the noise source.

These treatments are beneficial for heat insulation as well as for sound insulation, but acoustical windows are typically non -operable and central ventilation or air conditioning is needed. Residents' preferences should be considered.

If needed, additional building sound insulation can be provided by sealing vents and ventilation openings and relocating them to a side of the building away from the noise source. In cases where the noise sources is low - frequency noise from diesel locomotives, it may be necessary to increase the mass of the building facade for wood -frame houses by adding a layer of sheathing to the exterior walls.

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Examples of residential sound insulation for rail or highway projects are limited. However, much practical experience with sound insulation of buildings has been gained through grants for noise mitigation to local airport authorities by FAA.
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SECTION Transit Vibration
5 This section presents the basic concepts of transit ground -borne vibration, also referred throughout this manual as simple "vibration," and low -frequency groundborne-noise that sometimes results from vibration. The steps for the screening and assessing of potential vibration impacts of transit projects for FTA NEPA approval are described in the following sections.

The Source -Path -Receiver framework for ground -borne vibration for a rail system illustrated in Figure 5-I is central to all environmental vibration studies.

The train wheels rolling on the rails create vibration energy that is transmitted through the track support system into the transit structure. The vibration of the transit structure excites the adjacent ground, creating vibration waves that propagate through the ground and into nearby buildings creating ground -borne vibration effects that potentially interfere with activities. The vibrating building components may radiate sound, which this manual refers to as ground -borne noise. Airborne noise from transit sources is covered in Sections 2.3-4.5 of this manual. Ground -borne noise refers to the noise generated by ground -borne vibration.

AAP _
ro
Soil VibrationPropagationPath Structural Vibration
Radiated Sound
Figure 5-1 Propagation of Ground -Borne Vibration into Buildings This section contains the following:
• Section 5. I The ground -borne vibration and noise metrics used in this manual
• Section 5.2 An overview of transit vibration sources
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• Section 5.3 An overview of transit vibration paths
• Section 5.4 An overview of receiver factors of transit vibration and a discussion of the technical background for ground -borne noise criteria

5.1 Ground -Borne Vibration and Noise Metrics
Vibration is an oscillatory motion that can be described in terms of the displacement, velocity, or acceleration. Because the motion is oscillatory, there is no net movement of the vibration element and the average of any of the motion metrics is zero. Displacement is the most intuitive metric. For a vibrating floor, the displacement is simply the distance that a point on the floor moves away from its static position. The velocity represents the instantaneous speed of the floor movement and acceleration is the rate of change of the speed.

Although displacement is easier to understand than velocity or acceleration, it is rarely used for describing ground -borne vibration. Most transducers used for measuring ground -borne vibration use either velocity or acceleration.

Furthermore, the response of humans, buildings, and equipment to vibration is more accurately described using velocity or acceleration.

This manual uses the metrics outlined in Table 5-I for transit ground -borne vibration and noise measurements, computations, and assessment. These metrics are consistent with common usage in the United States.

Table 5-I Ground -borne Vibration and Noise Metrics
Metric
Abbreviation
Definition
Vibration Decibels
VdB
The vibration velocity level in decibel scale.

Peak Particle Velocity
PPV
The peak signal value of an oscillating vibration velocity waveform.

Usually expressed in inches/second in the United States.

Root Mean Square
rms
The square root of the arithmetic average of the squared amplitude of the signal.

A -weighted Sound Level
dBA
A -weighted sound levels represent the overall noise at a receiver that is adjusted in frequency to approximate typical human hearing sensitivity. This unit is used to characterize ground -borne noise.

The metrics in the table above are illustrated in Figure 5-2. The components in the figure include:
• Raw signal — This curve shows the instantaneous vibration velocity, which fluctuates positively and negatively about the zero point. • Peak particle velocity (PPV) — PPV is the maximum instantaneous positive or negative peak of the vibration signal. PPV is often used in monitoring of construction vibration (such as blasting) since it is related to the stresses that are experienced by buildings and is not used to evaluate human response.
• Root mean square (rms) velocity — Because the net average of a vibration signal is zero, the rms amplitude is used to describe smoothed vibration amplitude. The rms of a signal is the square root of the FEDERAL TRANSIT ADMINISTRATION 1 10
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average of the squared amplitude of the signal. The average is typically calculated over a one -second period. The rms amplitude is always less than the PPV(vi0 and is always positive. The rms amplitude is used to convey the magnitude of the vibration signal felt by the human body, in inches/second.

Figure 5-2 Vibration Signal in Absolute Units
The PPV and rms velocity are described in inches per second in the United States and meters per second internationally (with several different reference values). Although it is not universally accepted, vibration is commonly expressed in decibel notation. The decibel scale compresses the range of numbers required to describe vibration.

The graph in Figure 5-3 shows the rms curve from Figure 5-2 expressed in decibels.

Vibration velocity level in decibels is defined as:
v
L„ = 20 log
vret.
where:

Lv = velocity level, VdB
v = rms velocity amplitude
= I x I0-6in/sec in the USA
vref = I x l0"em/sec internationally'
Eq. 5-1
`Because of the variations in the reference quantities, it is important to be clear about what reference quantity is being used when specifying velocity levels. All vibration levels in this manual are referenced to Ix 10-6 inches/second.
vii The ratio of PPV to maximum rms amplitude is defined as the crest factor for the signal. The crest factor is typically greater than 1.41, although a crest factor of 8 or more is not unusual for impulsive signals. For ground -borne vibration from trains, the crest factor is usually 4 to 5.

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Signal in Terms of RMS Velocity Decibels
60 Velocity Level -- VdB
5 50
45 40 _
Maximum IIMS Level
8 9
2 3 4 5 6 7
Time
Figure 5-3 Vibration Signal in RMS Velocity Decibels
Ground -borne noise occurs when vibration radiates through a building interior and creates a low -frequency sound, often described as a rumble, as a train passes by. The annoyance potential of ground -borne noise is typically characterized with the A -weighted sound level. Although the A -weighted sound level is typically used to characterize community noise, characterizing low - frequency noise using A -weighting can be challenging because the non -linearity of human hearing causes sounds dominated by low -frequency components to seem louder than broadband sounds (sounds consisting of many frequency components, with no dominant frequencies) that have the same A -weighted level. The result is that ground -borne noise with a level of 40 dBA sounds louder than 40 dBA broadband noise. Because ground -borne noise sounds louder than broadband noise at the same noise level, the limits for ground - borne noise are lower (i.e., stricter) than would be the case for broadband noise.

5.2 Sources of Transit Ground -borne Vibration
and Noise
Ground -borne vibration can be a concern for nearby neighbors of a transit system route or maintenance facility. However, in contrast to airborne noise, ground -borne vibration is not a common environmental problem. It is unusual for vibration from sources such as buses and trucks to be perceptible, even in locations close to major roads. This section discusses common sources of ground -borne vibration and noise.

Most perceptible indoor vibration is caused by sources within buildings such as operation of mechanical equipment, movement of people, or slamming of doors.

Typical outdoor sources of vibration waves that propagate through the ground and create perceptible ground -borne vibration in nearby buildings include construction equipment, steel -wheeled trains, and traffic on rough roads. If the roadway is fairly smooth, the vibration from rubber -tired traffic is rarely perceptible. Building damage due to vibration is also rare for typical transportation projects; but in extreme cases, such as during blasting or pile - driving during construction, vibration could cause damage to buildings.

Figure 5-4 illustrates common vibration sources and the human and structural response to ground -borne vibration ranging from approximately 50 VdB (below FEDERAL TRANSIT ADMINISTRATION 1 12
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perceptibility) to 100 VdB (the threshold of potential damage). The background vibration velocity level in residential areas is usually 50 VdB or lower,lix1 and the threshold of perception for humans is approximately 65 VdB. A vibration level of 85 VdB in a residence can result in strong annoyance.

Human/Structural Response
Threshold for risk of minor cosmetic
damage for fragile buildings
Velocity Typical Sources
Level` (50 ft from source)
Difficulty with tasks such as —..-
reading a computer screen
Residential annoyance, infrequent
events (e g commuter rail)
Residential annoyance, frequent
events (e g rapid transit)
Limit for vibration sensitive —.-
equipment Approx. threshold for
human perception of vibration
-4e Blasting from construction projects
- Bulldozers and other heavy tracked
construction equipment
-4— Commuter rail, upper range
- Rapid transit, upper range
t— Commuter rail, typical
-4— Bus or truck over bump
"4c Rapid transit, typical
- Bus ortruck,typical
�— Typical background vibration
` RMS Vibration Velocity Level in VdB relative to 10-6 inches/second Figure 5-4 Typical Levels of Ground -Borne Vibration
Rapid transit or light rail systems typically generate vibration levels of 70 VdB or more near their tracks, while buses and trucks rarely create vibration that exceeds 70 VdB unless there are bumps due to frequent potholes in the road.

Heavy locomotives on diesel commuter rail systems create vibration levels approximately 5 to 10 dB higher than rail transit vehicles.

Vibration from trains is strongly dependent on factors such as how smooth the wheels and rails are, as well as the resonance frequencies of the vehicle suspension system and the track support system. These systems, like all mechanical systems, have resonances that result in increased vibration response at certain frequencies, called natural frequencies. Unusually rough road or track, steel -wheel flats, geologic conditions that promote efficient propagation of vibration, or vehicles with very stiff suspension systems could increase typical ix Background vibration is typically well below the threshold of human perception and is of concern only when the vibration affects very sensitive manufacturing or research equipment. Electron microscopes and high -resolution lithography equipment are examples of equipment that is highly sensitive to vibration.

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vibration levels by approximately I O VdB. Common factors that contribute to ground -borne vibration and noise at the source are presented in Table 5-2.

These factors are discussed in more detail throughout this Section.

Table 5-2 Factors that Influence Levels of Ground -Borne Vibration and Noise at the Source Category
Factors
Influence
Operations
and
Vehicles
Speed
Higher speeds result in higher vibration levels. Doubling speed results in a vibration level increase of approximately 4 to 6 dB.

Vehicle
Suspension
Stiff suspension in the vertical direction can increase the effective vibration forces. On transit cars, the primary suspension has the largest effect on vibration levels.

Wheel
Condition
and Type
Wheel flats and general wheel roughness are major sources of vibration from steel wheel/steel rail systems. Resilient wheels on rail transit systems can provide some vibration reduction over solid steel wheels, but are usually too stiff to provide substantial reduction. For more information, see Section 6.4, Step 2.

Guideway
Track/Roadway
Surface
Rough track or rough roads are often sources of excessive vibration. Maintaining a smooth surface will reduce vibration levels.

Track Support
System
On rail systems, the track support system is one of the major components in determining the levels of vibration. The highest vibration levels are created by track that is rigidly attached to a concrete trackbed (e.g., track on wood half -ties embedded in the concrete). The vibration levels are much lower when special vibration control track systems such as resilient fasteners, ballast mats, and floating slabs are used.

Transit
Structure
Heavier transit structures typically result in the lower vibration levels. The vibration levels from a lightweight bored tunnel will usually be higher than from a poured concrete box subway.

Transit System
Elevation
A rail system guideway will be either underground (subway), at -grade, or elevated, with substantial differences in the vibration characteristics at each elevation.
• Underground: vibration is typically the most important environmental factor of interest.
• At -grade: airborne noise is typically the dominant factor, although vibration and noise can be a problem, particularly at interior locations well isolated from exterior noise.
• Elevated: it is rare for vibration to be an issue with elevated railways except when guideway supports are located within 50 ft of buildings.

Brief discussions of ground -borne vibration and noise sources for different modes of transit are provided below.

At -Grade Heavy Rail and Light Rail
Ground -borne vibration and noise from urban heavy rail and LRT is common when there is less than 50 ft between the track and building foundations. Local geology and structural details of the building determine if the source of complaints is due to perceptible vibration or audible ground -borne noise.

Complaints about ground -borne vibration from surface track are more common than ground -borne noise complaints. A substantial percentage of complaints about both ground -borne vibration and noise correlate with proximity of special track work, rough or corrugated track, or wheel flats. Light rail systems tend to generate fewer complaints than heavy rail due to lower operating speeds.

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Commuter and Intercity Passenger Trains
There is the potential for vibration -related issues when new commuter or intercity rail passenger service (including electric multiple units (EMUs) and diesel multiple units (DMUs)) powered by either diesel or electric locomotives is introduced in an urban or suburban area. Commuter and intercity passenger trains have similar characteristics, but commuter trains typically operate on a more frequent schedule. These passenger trains often share track with freight trains, which have different vibration characteristics as discussed below.

Freight Trains
Local and long-distance freight trains are similar in that they both are diesel - powered and have the same types of cars. They differ in their overall length, number and size of locomotives, and number of heavily loaded cars. However, because locomotive suspensions are similar, the maximum vibration levels of local and long-distance freights are similar. Locomotives and rail cars with wheel flats are the sources of the highest vibration levels.

If the transit project does not in any way change the freight service, tracks, etc., then vibration from the freight line would be part of the existing conditions and need to be considered in terms of cumulative impacts (see Section 6.2, Step 3 on how to consider cumulative impacts). If the project results in changes to the freight path, operations, frequency, etc. (e.g., relocating freight tracks within the ROW to make room for the transit tracks) then those potential impacts and mitigation should be evaluated as part of the proposed project. However, note that vibration mitigation is very difficult to implement on tracks where freight trains with heavy axle loads operate.

High -Speed Passenger Trains
Passenger trains travelling at high speeds, 90 to 250 miles per hour, have the potential for creating high levels of ground -borne vibration. Ground -borne vibration should be anticipated as one of the major environmental impacts of any trains travelling at high speeds located in an urban or suburban area.(x) For projects that are specifically high-speed transportation refer to the FRA "High - Speed Ground Transportation Noise and Vibration Impact Assessment" guidance manual.(39)
AGT Systems
AGT systems include a wide range of transportation vehicles that provide local circulation in downtown areas, airports, and theme parks. Because AGT systems normally operate at low speeds, have lightweight vehicles, run on elevated structures, and rarely operate in vibration -sensitive areas, ground - borne vibration problems are very rare.

Subway and At -grade Track
While ground -borne vibration produced from trains operating subway and at - grade track have very different characteristics, they have comparable overall vibration velocity levels. Complaints about ground -borne vibration are often more common near subways than near at -grade track. This is not because Amtrak trains (branded Acela at the time of publication) on the Northeast Corridor between Boston and Washington, DC, which attain moderate to high speeds in some sections with improved track, fit into this category.

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subways create higher vibration levels than at -grade systems, rather because subways are usually located in more densely developed areas in closer proximity to building foundations, and the airborne noise is usually a more serious problem for at -grade systems than the ground -borne vibration. Another difference between subway and at -grade track is that the ground -borne vibration from subways tends to be higher frequency than the vibration from at - grade track, which makes the ground -borne noise more noticeable.

Streetcars
Complaints about ground -borne vibration from street cars are uncommon given that streetcars typically operate at very low speeds (less than 25 mph).

Buses
Because the rubber tires and suspension systems of buses provide vibration isolation, it is unusual for buses to cause ground -borne vibration or noise problems. For most issues with bus -related vibration, such as rattling of windows, the cause is almost always airborne noise and directly related to running surface conditions such as potholes, bumps, expansion joints, or other discontinuities in the road surface (usually resolved by smoothing the discontinuities).

Buses operating inside buildings will likely cause vibration concerns for other building inhabitants. An example of this situation is a bus transfer station in the same building as commercial office space. Sudden loading of a building slab by a heavy moving vehicle or by vehicles running over lane divider bumps can cause intrusive building vibration.

5.3 Paths of Transit Ground -Borne Vibration and
Noise
Vibration travels from the source through the transit structure and excites the adjacent ground, creating vibration waves that propagate through soil layers and rock strata to the foundations of nearby buildings. The vibration then propagates from the foundation throughout the remainder of the building structure. The vibration of the building structure and room surfaces can radiate a low -frequency rumble called ground -borne noise (Figure 5-I).

Soil and subsurface conditions are known to have a strong influence on the levels of ground -borne vibration. Among the most important factors are the stiffness and internal damping of the soil and the depth to bedrock. Vibration propagation is more efficient in stiff clay soils. Shallow rock may concentrate the vibration energy close to the surface, resulting in ground -borne vibration problems at large distances from the track. Factors such as soil layers and depth to water table can have substantial effects on the propagation of ground -borne vibration. These factors are summarized in Table 5-3.

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Table 5-3 Factors that Influence Levels of Ground -borne Vibration and Noise along Path Geology Factors
Influence
Soil type
Vibration levels are generally higher in stiff clay -type soil than in loose sandy soil.

Rock layers
Vibration levels are usually high near at -grade track when the depth to bedrock is 30 ft or less. Subways founded in rock will result in lower vibration amplitudes close to the subway. Vibration levels do not attenuate as rapidly in rock as in soil.

Soil layering
Soil layering can have a substantial effect on the vibration levels since each stratum can have considerably different dynamic characteristics.

Depth to water table
The presence of the water table may have a substantial effect on vibration, but a definite relationship has not been established.

5.4 Receiver Factors that Influence Ground -
Borne Vibration and Noise
Ground -borne vibration is a concern almost exclusively inside buildings. Train vibration may be perceptible to people who are outdoors, but it is very rare for outdoor vibration to cause complaints.

The vibration levels inside a building are dependent on the vibration energy that reaches the building foundation, coupling of the building foundation to the soil, and propagation of the vibration through the building. In general, the heavier a building is, the lower the response will be to the incident vibration energy.

Common factors that contribute to ground -borne vibration and noise at the receiver are presented in Table 5-4.

Table 5-4 Factors that Influence Levels of Ground -Borne Vibration and Noise at the Receiver Receiver Building
Factors
Influence
Foundation type
The heavier the building foundation, the greater the coupling loss as the vibration propagates from the ground into the building.

Building
construction
Each building has different characteristics relative to structure -borne vibration, but, in general, the heavier the building, the lower the levels of vibration. The maximum vibration amplitudes of the floors and walls of a building will often occur at the resonance frequencies of the components of the building.

Acoustical
absorption
The more acoustically absorptive materials in the receiver room, the lower the ground -borne noise level. Note that because ground -borne noise usually is a low - frequency phenomenon, it is affected by low -frequency absorption (e.g., below 250 Hz).

5.5 Human Response to Transit Ground -borne
Vibration and Noise
This section contains an overview of human receiver response to ground -borne vibration and noise. It serves as background information for the vibration impact criteria in Section 6.2.

The effects of ground -borne vibration can include perceptible movement of floors in buildings, rattling of windows, shaking of items on shelves or hanging on walls, and low -frequency noise (ground -borne noise). Building damage is not a FEDERAL TRANSIT ADMINISTRATION 117
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factor for typical transportation projects, but in extreme cases, such as during blasting or pile -driving during construction, vibration could cause damage to buildings. Although the perceptibility threshold is approximately 65 VdB, human response to vibration is not usually substantial unless the vibration exceeds 70 VdB (Figure 5-4). A vibration level that causes annoyance is well below the damage risk threshold for typical buildings (100 VdB).

Ground -borne vibration is almost never a problem outdoors. Although the motion of the ground may be perceived, without the effects associated with the shaking of a building, the motion does not provoke the same adverse human reaction. Ground -borne noise that accompanies the building vibration is usually perceptible only inside buildings and typically is only an issue at locations with subway or tunnel operations where there is no airborne noise path or for buildings with substantial sound insulation such as a recording studio.

One of the challenges in developing suitable criteria for ground -borne vibration is that there has been relatively little research into human response to vibration and, specifically, human annoyance with building vibration. The American National Standards Institute (ANSI) developed criteria for evaluation of human exposure to vibration in buildings in I983,(40) and the International Organization for Standardization (ISO) adopted similar criteria in I989(4') and revised them in 2003.(42) The 2003 version of ISO 2631-2 acknowledges that "human response to vibration in buildings is very complex." It further indicates that the degree of annoyance cannot always be explained by the magnitude of the vibration alone.

In some cases, complaints are associated with measured vibration that is lower than the perception threshold. Other phenomena such as ground -borne noise, rattling, visual effects such as movement of hanging objects, and time of day (e.g., late at night) all play some role in the response of individuals. To understand and evaluate human response, which is often measured by complaints, all of these related effects need to be considered.

Figure 5-5 illustrates the relationship between the vibration velocity level measured in 22 homes and the general response of the occupants to the vibration from measurements performed for several transit systems along with subjective ratings by researchers and residents. These data are published in the "State -of -the -Art Review of Ground -borne Noise and Vibration."(43) The figure also includes a curve representing the percent of people annoyed by vibration from high-speed trains from a Japanese study for comparison.(44) Both the occupants and the people who performed the measurements agreed that floor vibration in the Distinctly Perceptible range is unacceptable for a residence. The data indicates that residential vibration exceeding 75 VdB is unacceptable for a repetitive vibration source such as rapid transit trains that pass every 5 to 15 minutes. The results from the Japanese study confirm the conclusion that at a vibration velocity level of 75 to 80 VdB, many people will find the vibration annoying. A Transportation Research Board (TRB) study of human response to vibration from 2009 also supports this finding and indicates that incidence of complaints fall rapidly with a level decreasing below 72 Vd B.(42)(45)
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Response to Residential Building Vibration
4 to 15 Rapid Transit Trains per Hour
Disagreeable
Distinctly
Perceptible
Barely
Perceptible
Imperceptible
%Annoyed
▪ 4-'S ▪ no 0 8 r
$o sa
esponse to Rapid
Transit Trains
Range of Response to
Rapid Transit Trains
Response to High -
Speed Trains
i 1
55 60 65 70 75 80 85
Vibration Velocity Level -- dB re 1 micro inisec
100
80 BO
0 C
40 0
20 o
9D
Figure 5-5 Response to Transit -Induced Residential Vibration Table 5-5 presents the human response to different levels of ground -borne vibration and noise on which the criteria presented in Section 6.2 are based.

The vibration level (VdB) is presented with the corresponding frequency assuming that the vibration spectrum peaks at 30 Hz or 60 Hz.(xi) The ground - borne noise levels (dBA) are estimated for the specified vibration velocity with a peak vibration spectrum of 30 Hz (Low Freq) and 60 Hz (Mid Freq). Note that the human response differs for vibration velocity level based on frequency. For example, the noise caused by vibrating structural components may cause annoyance even though the vibration cannot be felt. Alternatively, a low - frequency vibration can cause annoyance while the ground -borne noise level it generates does not.
xi The A -weighted level of ground -borne noise can be estimated by applying A -weighting to the vibration velocity spectrum and by subtracting an additional 5 dB for a room with average acoustical absorption. Since the A -weighting at 31.5 Hz is -39.4 dB, if the vibration spectrum peaks at 30 Hz, the A -weighted sound level will be approximately 40 dB lower than the velocity level. If the vibration spectrum peaks at 60 Hz, the A -weighted sound level will be approximately 25 dB lower than the velocity level.

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Table 5-5 Human Response to Different Levels of Ground -Borne Vibration and Noise Vibration
Velocit Level
y
Noise Level
Human Response
Low
Freq*
Mid
Freq**
65 VdB
25 dBA
40 dBA
Approximate threshold of perception for many humans. Low - frequency sound: usually inaudible. Mid -frequency sound: excessive for quiet sleeping areas.
75 VdB
35 dBA
50 dBA
Approximate dividing line between barely perceptible and distinctly perceptible. Many people find transit vibration at this level annoying.

Low -frequency noise: tolerable for sleeping areas. Mid -frequency noise: excessive in most quiet occupied areas.
85 VdB
45 dBA
60 dBA
Vibration tolerable only if there are an infrequent number of events per day. Low -frequency noise: excessive for sleeping areas. Mid - frequency noise: excessive even for infrequent events for some activities.
*Approximate noise level when vibration spectrum peak is near 30 Hz. **Approximate noise level when vibration spectrum peak is near 60 Hz. 01-31
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SECTION Vibration Impact Analysis
6 The FTA vibration impact analysis process is a multi -step process used to evaluate a project for potential vibration impacts. If impact is determined, measures necessary to mitigate adverse impacts are to be considered for incorporation into the project.(;)
The FTA vibration impact analysis steps are summarized as follows and are described in the following sections:

6.1 Determine vibration analysis level.

6.2 Determine vibration impact criteria.

Option A: General Vibration Assessment Criteria
Option B: Vibration Impact Criteria for a Detailed Vibration Analysis

6.3 Evaluate Impact: Vibration Screening Procedure
Step 1: Classify project vehicles.

Step 2: Determine project type.

Step 3: Determine screening distance.

Step 4: Identify vibration -sensitive land uses.

6.4 Evaluate Impact: General Vibration Assessment.

Step I : Select base curve for ground surface vibration level.

Step 2: Apply adjustments.

Step 3: Inventory vibration impact.

6.5 Evaluate Impact: Detailed Vibration Analysis
Step I: Characterize Existing Vibration
Step 2: Estimate Vibration Impact
Step 3: Assess Vibration Impacts
Step 4: Determine Vibration Mitigation Measures
A similar process for the noise impact analysis is presented in Section 4. After the noise and vibration analyses have been completed, assess construction noise and vibration according to Section 7 and document findings according to Section 8.

6. I Determine Vibration Analysis Level
There are three levels of analysis to assess the potential ground -borne vibration and noise impacts resulting from a public transportation project. The appropriate level of analysis varies by project based on the type and scale of the project, the stage of project development, and its environmental setting. These three levels are: the Vibration Screening Procedure, the General Vibration Assessment, and the Detailed Vibration Analysis. These levels of vibration analysis mirror the levels of noise analysis discussed in Section 4.2.

The Vibration Screening Procedure, performed first, defines the study area of any subsequent vibration impact assessment. Where there is potential for FEDERAL TRANSIT ADMINISTRATION 121
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impact, the General Vibration Assessment and Detailed Vibration Analysis procedures are used to determine the extent and severity of impact. In some cases, a General Vibration Assessment may be all that is needed. However, if the proposed project is near noise -sensitive land uses and it appears at the outset that the impact would be substantial, it is prudent to conduct a Detailed Vibration Analysis.

The methods for analyzing transit vibration are consistent with those described in recognized handbooks and international standards.(46)(") Conduct the vibration screening procedure and then determine the appropriate vibration analysis option:

Vibration Screening Procedure — The Vibration Screening Procedure is a simplified method of identifying the potential for vibration impact from transit projects. The Vibration Screening Procedure is applicable to all types of transit projects and does not require any specific knowledge about the vibration characteristics of the system or the geology of the area. This procedure uses simplified assumptions and considers the type of project and the presence or absence of vibration -sensitive land uses within a screening distance that has been developed to identify most potential vibration impacts. If no vibration -sensitive land uses are present within the defined screening distance, then no further vibration assessment is necessary.

The Vibration Screening Procedure steps are provided in Section 6.3, Step I.

General Vibration Assessment — The General Vibration Assessment is used to examine potential impacts to vibration -sensitive land use areas identified in the screening step more closely. It uses generalized information likely to be available at an early stage in the project development process and during the development of most environmental documents.

Vibration levels at receivers are determined by estimating the overall vibration velocity level and A -weighted ground -borne noise levels as a function of distance from the track and applying adjustments to account for factors such as track support systems, vehicle speed, type of building, and track and wheel conditions.

A General Vibration Assessment is sufficient for the environmental review of many projects, including projects that compare transit modal alternatives or relocate a crossover or turnout. The General Vibration Assessment may also be sufficient if it results in a commitment to mitigation that eliminates the vibration impacts, such as a change in transit mode or alignment. However, if impact is identified through the General Vibration Assessment procedures and not mitigated, a Detailed Vibration Analysis of the selected alternative must be completed. Most vibration mitigation measures can only be specified after a Detailed Vibration Analysis has been done.

The General Vibration Assessment procedure is provided in Section 6.3, Step 2.

Detailed Vibration Analysis — The Detailed Vibration Analysis procedure is a comprehensive assessment method that produces the most accurate estimates FEDERAL TRANSIT ADMINISTRATION I22
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of vibration impact for a proposed project and is often accomplished during the engineering phase of a project when there are sufficient data identifying potential adverse vibration impacts from the project. However, a Detailed Vibration Analysis may be warranted earlier in the environmental review process if there are potentially severe impacts due to the proximity of vibration - sensitive land uses. This type of assessment requires professionals with experience in performing and interpreting vibration propagation tests.

A Detailed Vibration Analysis may not be necessary for all segments of a project. Generalized prediction curves from the General Vibration Assessment procedures may be sufficient for most of the alignment, and the Detailed Vibration Analysis procedure may only need to be applied to particularly sensitive receivers (Section 6.3). Note that a Detailed Vibration Analysis is typically required when designing special track -support systems such as floating slabs or ballast mats. These and other costly vibration mitigation measures can only be specified after a Detailed Vibration Analysis has been done in the engineering phase of the project.

The Detailed Vibration Analysis procedure is presented in Section 6.3, Step 3.

6.2 Determine Vibration Impact Criteria
Use the FTA criteria presented in this section when conducting a General Vibration Assessment or a Detailed Vibration Assessment. Like noise, the sensitivity to vibration varies by land use type, and the criteria represent these sensitivities. These criteria are based on national and international standards,i3B11391(4B) as well as experience on human response to building vibration. See Section 5.5 for additional background information on the development of FTA vibration criteria. The criteria for environmental impact from ground -borne vibration and noise are based on the maximum root - mean -square (rms) vibration velocity levels for repeated events of the same source.

Determine the appropriate criteria based on the level of analysis (Section 6. I ).

The impact criteria for the General Vibration Assessment are presented in Option A, and the impact criteria for the Detailed Vibration Analysis are presented in Option B.

Option A: General Vibration Assessment Criteria
Determine the land use according to Step I and the frequency of events according to Step 2. The impact criteria for the General Vibration Analysis are presented in Step 3.

Step I: Land Use Categories
Determine the appropriate land use category for the receiver of vibration impacts of the project or project segment. Sensitive land use categories for vibration assessment are presented in Table 6-I in order of sensitivity. Consider indoor use of the buildings when determining land use categories for ground -borne vibration and noise, since impact is experienced indoors.

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Table 6- I Land Use Categories for General Vibration Assessment Impact Criteria Land Use
Category
Land Use
Type
Description of Land Use Category
Special
Buildings
This category includes special -use facilities that are very sensitive to vibration and noise that are not included in the categories below and require special consideration.

However, if the building will rarely be occupied when the source of the vibration (e.g., the train) is operating, there is no need to evaluate for impact. Examples of these facilities include concert halls, TV and recording studios, and theaters.

High
Sensitivity
This category includes buildings where vibration levels, including those below the threshold of human annoyance, would interfere with operations within the building.

Examples include buildings where vibration -sensitive research and manufacturing* is conducted, hospitals with vibration -sensitive equipment, and universities conducting physical research operations. The building's degree of sensitivity to vibration is dependent on the specific equipment that will be affected by the vibration.

Equipment moderately sensitive to vibration, such as high resolution lithographic equipment, optical microscopes, and electron microscopes with vibration isolation systems are included in this category.** For equipment that is more sensitive, a Detailed Vibration Analysis must be conducted.
2 Residential
This category includes all residential land use and buildings where people normally sleep, such as hotels and hospitals. Transit -generated ground -borne vibration and noise from subways or surface running trains are considered to have a similar effect on receivers.***
3 Institutional
This category includes institutions and offices that have vibration -sensitive equipment and have the potential for activity interference such as schools, churches, doctors' offices. Commercial or industrial locations including office buildings are not included in this category unless there is vibration -sensitive activity or equipment within the building. As with noise, the use of the building determines the vibration sensitivity. * Manufacturing of computer chips is an example of a vibration -sensitive process. ** Standard optical microscopes can be impacted at vibration levels below the threshold of human annoyance. *4* Even in noisy urban areas, the bedrooms will often be in quiet buildings with effective noise insulation. However, ground - borne vibration and noise are experienced indoors, and building occupants have practically no means to reduce their exposure. Therefore, occupants in noisy urban areas are just as likely to be exposed to ground -borne vibration and noise as those in quiet suburban areas.
• Ground -borne Vibration — Locations with equipment that is highly - sensitive to vibration should be included in category I or assessed using the Detailed Vibration Analysis procedures (Section 6.3, Step 3) and criteria (Section 6.2, Option B) or specific criteria of the equipment manufacturer.

Most computer installations or telephone switching equipment is not considered sensitive to vibration. Although the owners of this type of equipment often are concerned with the potential for ground -borne vibration interrupting smooth operation of their equipment, it is rare for computer or other electronic equipment to be particularly sensitive to vibration. This type of equipment is typically designed to operate in common building environments where the equipment may experience occasional disturbances and continuous background vibration caused by other equipment.
• Ground -borne Noise — Ground -borne noise is typically only assessed at locations with subway or tunnel operations where there is no airborne noise path, or for buildings with substantial sound insulation such as a recording studio. For typical buildings with at -grade or elevated transit operations, the interior airborne noise levels are often higher than the FEDERAL TRANSIT ADMINISTRATION 124
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ground -borne noise levels. For interior rooms or other special cases, ground -borne noise may need to be assessed.

Step 2: Identify Event Frequency
Determine the appropriate frequency of events for the project or project segment.

Community response to vibration correlates with the frequency of events and, intuitively, more frequent events of low vibration levels may evoke the same response as fewer high vibration level events. This effect is accounted for in the ground -borne vibration and noise impact criteria by characterizing projects by frequency of events. Event frequency definitions are presented in Table 6-2.

Table 6-2 Event Frequency Definitions
Category
Definition
Typical Project Types
Frequent Events
More than 70 events per day
Most rapid transit
Occasional Events
30-70 events per day
Most commuter trunk lines
Infrequent Events
Fewer than 30 events per day
Most commuter rail branch lines
Step 3: Apply Impact Criteria by Land Use and Event
Frequency
Select the appropriate impact criteria for ground -borne vibration and noise based on the previously identified land use categories and frequency of events. It is also important to consider the time of vibration sensitivity. If the building is not typically occupied when the vibration source (e.g., train) is operating, it is not necessary to consider impact.

The criteria in this section are appropriate for assessing human annoyance or interference with vibration -sensitive equipment for common projects. While not typical, existing conditions, freight train operations, and building damage may require consideration.
• Existing Conditions — The criteria in this section do not consider existing conditions. In most cases, the existing environment does not include a substantial number of perceptible ground -borne vibration or noise events.

However, existing conditions must be evaluated in some cases, such as for projects located in an existing rail corridor. For criteria considering existing conditions, see Step 3b.
■ Freight Train Operations — The criteria are primarily based on experience with passenger train operations. Passenger train operations (rapid transit, commuter rail, and intercity passenger railroad) create vibration events that last approximately 10 seconds or less while a typical line -haul freight train event lasts approximately two minutes. This manual is oriented to transit projects. However, situations will occur when freight train operations must be evaluated, such as when freight train tracks are relocated for a transit project within a railroad ROW. Guidelines on applying these criteria to freight train operations are presented in Step 3c.

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• Building Damage — It is extremely rare for vibration from train operations to cause substantial or even minor cosmetic building damage.

However, damage to fragile historic buildings located near the ROW may be of concern. Even in these cases, damage is unlikely except when the track is located very close to the structure. Damage thresholds that apply to these structures are discussed in Section 7.2, Step 4 on Construction Vibration Impacts.
3a. Choose the impact criteria by land use category and event frequency. The criteria for ground -borne vibration and noise land use categories I -3 are presented in Table 6-3. The criteria are presented in terms of acceptable indoor ground -borne vibration and noise levels. Impact will occur if these levels are exceeded. Criteria for ground -borne vibration are expressed in terms of rms velocity levels in VdB, and criteria for ground -borne noise are expressed in terms of A -weighted sound pressure levels in dBA.

Table 6-3 Indoor Ground -Borne Vibration (GBV) and Ground -Borne Noise (GBN) Impact Criteria for General Vibration Assessment
Land Use Category
GBV Impact Levels
(VdB re I micro -inch /sec)
GBN Impact Levels
(dBA re 20 micro Pascals)
Frequent
Events
Occasional
Events
Infrequent
Events
Frequent
Events
Occasional
Events
Infrequent
Events
Category I : Buildings where
vibration would interfere with
interior operations.
65 VdB*
65 VdB'
65 VdB"
N/A**
N/A'
N/A"
Category 2: Residences and
buildings where people
normally sleep.
72 VdB
75 VdB
80 VdB
35 dBA
38 dBA
43 dBA
Category 3: Institutional land
uses with primarily daytime
use.
75 VdB
78 VdB
83 VdB
40 dBA
43 dBA
48 dBA
* This criterion limit is based on levels that are acceptable for most moderately sensitive equipment such as optical microscopes. For equipment that is more sensitive, a Detailed Vibration Analysis must be performed. ** Vibration -sensitive equipment is generally not sensitive to ground -borne noise; however, the manufacturer's specifications should be reviewed for acoustic and vibration sensitivity.

The criteria for ground -borne vibration and noise for special land uses are presented in Table 6-4. The criteria are presented in terms of acceptable indoor ground -borne vibration and noise levels. Impact will occur if these levels are exceeded. As for the other land uses, the criteria for ground -borne vibration are expressed in terms of rms velocity levels in VdB, and criteria for ground - borne noise are expressed in terms of sound pressure levels in dBA.

Table 6-4 Indoor Ground -Borne Vibration and Noise Impact Criteria for Special Buildings Type of Building or
Room
Ground -Borne Vibration Impact
Levels (VdB re I micro-inch/sec)
Ground -Borne Noise Impact
Levels (dBA re 20 micro -Pascals)
Frequent
Events
Occasional or
Infrequent Events
Frequent
Events
Occasional or
Infrequent Events
Concert halls
65 VdB
65 VdB
25 dBA
25 dBA
TV studios
65 VdB
65 VdB
25 dBA
25 dBA
Recording studios
65 VdB
65 VdB
25 dBA
25 dBA
Auditoriums
72 VdB
80 VdB
30 dBA
38 dBA
Theaters
72 VdB
80 VdB
35 dBA
43 dBA
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