3.5 CONCLUSION
Updating the City of Sacramento DOU’s stormwater hydraulic models would enhance system reliability, operational efficiency, and resilience in the face of evolving climate and urban challenges. Integrating current data, expanding model coverage, and incorporating future climate and land use scenarios will enable DOU to better predict and manage flood risks, optimize infrastructure investments, and ensure compliance with regulatory requirements. Implementing these best practices will position Sacramento to proactively address future uncertainties, safeguard public safety, and advance sustainability goals for a robust and effective stormwater management system.
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4| SHADING
4.1 STRUCTURAL SHADING
Introduction
In many locations, trees cannot be planted due to available space, utilities, and other urban area restrictive elements. Structural-based shading uses solid or semi-solid materials that block sunlight. Typically, the structure includes a frame, a canopy and/or panels, and posts that are anchored to the ground.
Purpose
The purpose of this document is to outline practical strategies for selecting, locating, and maintaining shade structures in transit environments and adjacent urban corridors.
Guidance is focused on early design and coordination, not on construction-level detail.
Emphasis is placed on solutions that perform well under Sacramento’s heat conditions and can be maintained over time. Because conditions and constraints vary widely, the strategies in this document are adaptable and intended for use across bus stops, light rail stations, transit centers, walkways, and public spaces.
Goals
This document aims to provide direction for heat-resilient shelter and shade-structure design; support coordinated decision-making among the City, SacRT, unincorporated Sacramento County, and SMUD; and provide tools to evaluate shading approaches.
How to Use This Document
Use the guidance during planning and early design to:
• Identify types of shade structures used to aid pedestrians and transit users. • Select materials used to construct shade structures that support heat resiliency. • Determine strategies to be used in shade structure design that provide ventilation and protection from the sun.
Shade Structure Types
• Bus Shelters
o Description: Bus stop shelters are small, semi-enclosed structures used to protect passengers from the elements while waiting for the bus. o Located: Behind sidewalks or alongside roads.
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o Size: Current shelter sizes vary between 8’, 10’, and 12’ in length. Typical dimensions are 5 ft x 12 ft; 60 sq-ft to 100 sq-ft. Height clearance should be at least 8 ft.
o Functions: Protects transit riders from rain, wind, and sun. Provides the required ADA clearance around the shelter unit for wheelchairs to navigate and access the sheltered stop. Provides visual cue of the location of a bus stop. o Potential integrated elements: Seating, digital informational signage, advertising, wind/sunscreen, roof, and lighting.
Photo: Bus Shelter in Citrus Heights, CA — Sacramento Regional Transit District
• Light Rail Station Platform Shade Structures
o Description: Light rail station platform shade structures are semi-enclosed structures used to protect passengers while waiting for light rail trains. o Located: Along the station platform and boarding areas, adjacent to the tracks. o Size: Typical dimensions 8 ft x 16 ft; 120 sq-ft to 300 sq-ft. Height clearance should be at least 9 ft.
o Functions: Protects transit riders from rain, wind, and sun. Provides the required ADA clearance around the unit for wheelchairs to navigate and access the
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station platform and boarding area. Provides visual cue of the location of a light rail station.
o Potential integrated elements: Seating, digital informational signage, advertising, wind/sunscreen, roof, security cameras, lighting.
Photo: Light Rail Platform Shade Structure at Franklin Station, Sacramento, CA — Sacramento Regional Transit District. (Note that installing screens between the posts could provide wind protection.)
• Transit Center / Pavilion
o Description: Transit center structures are semi-enclosed structures used to protect passengers while waiting for light rail trains, buses, and other modes of transit. This structure type is typically constructed to be more durable than a bus shelter or a light rail station platform structure. o Located: Along sidewalks, adjacent to tracks, or parking lots. o Size: 300 sq-ft and larger. Height clearance should be at least 9 ft.
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o Functions: Protects transit riders from rain, wind, and sun. Provides required ADA clearance around the structure for wheelchairs to navigate and access the platform and boardings areas for both buses and trains. Provides visual cue of the location of a transit center.
o Potential integrated elements: Seating, digital informational signage, advertising, wind/sunscreen and roof or enclosed area, security cameras, lighting. May also provide enough space to include restrooms and drinking water.
Photo: Transit Center Structure at 7th & Richards / Township 9 Station, Sacramento, CA — Sacramento Regional Transit District
• Covered Walkway
o Description: A structure that covers a walking path between two destinations.
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o The structure may be continuous or in segments between the destinations. o Located: Over sidewalks, for example connecting a transit stop to a park-and- ride lot or connecting two transit stops.
o Size: The length will vary, and width should be a minimum of 5 ft. Height clearance should be at least 9 ft.
o Functions: Protects pedestrians from rain and sun. Provides minimum width for pedestrians and individuals navigating in wheelchairs, with minimal columns and/or posts to not obstruct the path of travel. o Potential integrated elements: digital informational signage, roof, security cameras, lighting, and solar panels.
Photo: Covered Walkway at Sacramento Valley Station, Sacramento, CA — City of Sacramento / Sacramento Regional Transit District
• Carport
o Description: A carport is intended to cover automobile parking stalls and is designed to shade parked cars and portions of the parking lot to reduce heat.
Posts should be placed to not obstruct car doors. Placement of carports should not overhang drive aisles or obstruct fire access (i.e. fire trucks need at least 13’- 6” height clearance). The structure is built of durable materials and designed to withstand potential vehicle impacts. The carport structural design
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should consider extreme weather conditions like wind, rain, and heat. Solar panels are often mounted on top and can function as the roof. o Located: In parking lots covering parking stalls.
o Size: Size should be based on parking stall dimensions. Larger carports may require fire sprinklers and setbacks to surrounding structure and property lines.
Refer to building and zoning codes to determine size and setback requirements. Carport height clearance should be at least 9 ft. o Functions: To shade parking stalls to reduce heat in parking lots. Provide structure to mount solar panels, which in turn can generate electricity that may feed into electric-vehicle (EV) charging stations.
o Integrated elements: Roof, security cameras, lighting, and solar panels.
Photo: Solar Carport at Granite Bay High School, Granite Bay, CA — Roseville Joint Union High School District / New Era Electric
Materials and Heat-Resilience Strategies
Material Strategies
The structural components of built shade should be constructed from durable materials— such as concrete, steel, and stainless steel—to provide strength, long service life, low maintenance, and high resistance to impact and wear. Wall panels and roofing may use
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aluminum, aluminum composite material (ACM), and/or thermally modified wood to achieve durability, reduced surface temperatures, and minimal upkeep, with thermally modified wood reserved for locations where vandalism risk is low. Shade fabrics made from vinyl or high-density polyethylene plastic (HDPE) yarn and acrylic panels are not preferred due to their shorter service life, higher maintenance needs, and vulnerability to vandalism. Where appropriate, exposed surfaces are recommended to receive vandalism- resistant coatings, with reapplication anticipated every 5 to 20 years depending on the product type and site exposure.
Stainless Steel and Corten
Stainless steel and Corten are highly durable materials with long service lives and relatively low maintenance needs. Stainless steel may be used raw, brushed/textured, or painted, and both stainless steel and Corten are well suited to locations where corrosion is a concern or where ongoing coating maintenance is unlikely. However, both materials can become hot in direct sun and are more expensive than standard structural steel, so their use is typically strategic and limited to key elements or accents. Leaving them uncoated can help manage lifecycle costs. Corten is designed to develop a stable rust patina layer that protects the underlying steel and creates a distinctive weathered appearance, but this rust can stain adjacent paving and surfaces and should be detailed accordingly.
Concrete
Concrete is extremely durable and offers a very long service life. Cast-in-place concrete can achieve a high aesthetic quality with form liners, integral color, and protective or decorative coatings. It is often relatively expensive due to material and labor costs, and it can become hot in full sun. For ground surfaces, concrete is typically preferred and should use lighter colors to reduce heat gain. Where concrete is used on vertical elements, design to minimize prolonged direct sun exposure and favor lighter finishes to limit heat buildup.
Steel
Steel is highly durable with a long service life when properly protected, and its high strength-to-weight ratio allows efficient long spans and slender structural members. It is well suited for primary structural components such as posts, beams, rafters, and bracing.
Steel should not be used as exposed roofing or infill panels in full sun where heat gain and glare can be problematic. Because steel components can be fabricated off-site and then quickly assembled on-site, it can be a cost-effective option when paired with appropriate corrosion-resistant coatings and ongoing maintenance.
Aluminum
Aluminum is slightly less durable than steel but is roughly one-third lighter, allowing slimmer members and reduced structural support. It offers good corrosion resistance, and 58 | Page
surfaces can be left mill-finished or painted depending on aesthetic and maintenance goals. For shade structure applications, aluminum tubing and panels should generally be a minimum of ¼ inch thick to ensure durability and stiffness. Laser-cut aluminum panels can be used to provide shade, ventilation, and visual interest, turning functional elements into integral aesthetic features.
Composite and Plastic
Composite and plastic materials can offer cost savings while still providing good durability. “Composite” covers a broad range of products made from two or more materials— commonly combinations of wood fiber, fiberglass, carbon fiber, plastics, resins, concrete, or aluminum. Typical examples include fiber-reinforced polymer (FRP), wood–plastic composites, composite aluminum panels, cement-bonded wood fiber, and glass fiber– reinforced polymer. Aluminum composite material (ACM) are two thin layers of aluminum with a rigid plastic core bond between layers of aluminum. ACM is durable, lightweight, provides insulation, and reduces heat transfer using the plastic as a thermal brake.
An ACM panel has a very low heat transfer compared to other composite materials.
Performance and cost vary significantly based on the specific materials and manufacturing methods, and many products are designed to mimic the look of natural materials while improving durability, reducing maintenance, or simplifying installation. Any proposed composite or plastic product should be evaluated for structural performance, ultra-violet (UV) stability, vandal resistance, and expected service life before being specified.
Polycarbonate and Acrylic Panel
Acrylic panels offer good clarity and strong UV resistance but tend to be more brittle, while polycarbonate panels are significantly stronger, more impact resistant, and less prone to scratching. Both acrylic and polycarbonate can be manufactured as translucent or with varying levels of opacity, and when clear or low opacity, they admit substantial sunlight, often creating a greenhouse effect within a shade structure. Polycarbonate does require a UV coating to prevent discoloration and weakening from sun exposure over time, whereas acrylic maintains UV resistance without additional treatment. Because both materials transmit sunlight and can contribute to heat gain, tinted or frosted options may be used to reduce thermal buildup, and in all cases the panels should be specified with sufficient thickness to withstand impact.
Thermally Modified Wood
Thermally modified wood is natural lumber that is treated with heat and steam to improve durability, increase hardness, enhance resistance to decay and pests, and reduce moisture movement, which can also improve fire performance. It offers many benefits associated with tropical hardwoods such as teak and ipe, but is typically produced from 59 | Page
more sustainable species. The material can be oiled to retain its original color or left unfinished to weather to a silvery grey. Although thermally modified wood is more expensive than species like redwood or cedar, it generally provides a longer service life with reduced maintenance needs. Where a real-wood appearance is desired, thermally modified wood is the preferred option.
Tensile Fabric
Tensile fabric shade structures rely on substantial steel posts and foundations, which can make them relatively expensive to construct. They also require ongoing maintenance: at a minimum, quarterly inspections of the structure, cables, and fittings to check for tension loss, wear, and damage, plus annual re-tensioning to maintain performance and safety.
Fabric membranes should be cleaned each year, which can be challenging on larger or higher canopies. HDPE yarn fabrics are breathable and allow some light and rain to pass through, providing shade without full weather protection. PVC-coated fabrics are non- breathable and waterproof but can trap heat beneath the canopy; their durability improves with material weight, and a minimum of 32 oz fabric is recommended for extended service life.
Shade Structure Materials Matrix
Table 7. Material matrix of shade structures
Materials
Expected
Service
Life
(Years) Durability Maintenance
Vandal
Resistance
Heat
Transfer
Resilience Cost
Stainless
Steel/ Corten 50+ 5 5 5 2 5
Concrete 50+ 5 4 5 2 4
Steel (powder
coated) 40-50 5 3 5 2 3
Aluminum 30-40 4 4 4 3 3
Composite/
Plastic 20-30 3 4 3 2* 2
Polycarbonate
Panel 20-30 4 4 3 3 3
Thermal
Modified
Wood
20-25 3 2 2 4 3
Shade Fabric
PVC coated 15-20 3 3 3 4 4
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Acrylic Panel 15-20 3 3 2 3 2
Shade Fabric
HDPE Yarn 10-15 2 3 2 5 3
Notes:
Scale (1–5): 5 = Excellent / High, 1 = Poor / Low.
Expected Service Life: Approximate years under typical outdoor urban exposure with proper maintenance and recoating.
Heat Transfer: Higher numbers mean better resilience (lower heat transfer and absorption).
Cost: High = higher cost. Relative initial material + installation cost (not lifecycle).
Heat Resilient Bus Shelter Typologies and Solar Orientation Bus Shelter with North or East Exposure
This shelter design uses perforated aluminum panels to maximize sun screening and allow ventilation. The structure has sides open from below to the optimal height to allow ventilation. The aluminum roof has a high Solar Reflective Index and is elevated high enough to reduce heat transmission to shelter occupants.
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Bus Shelter with South or West Exposure
This shelter design uses perforated panels and louvers to maximize sun screening and allow ventilation. The structure has sides open to the greatest extent possible to allow ventilation. The roof has a high Solar Reflective Index and is elevated high enough to reduce heat transmission to occupants.
Retrofitting Bus Shelter
Existing bus shelters with glass and/or polycarbonate side panels and roofs can be retrofitted with aluminum panels to improve heat resilience. Replacing solid glazing and increasing open area or perforation improves airflow and reduces heat buildup. Perforated aluminum side panels provide ventilation while still offering shade and low-angle sun protection, and solid aluminum roof panels increase shade and reflect solar gain. A structural review of the shelter frame is required before adding or replacing panels, and the original shelter manufacturer should be consulted to confirm compatibility with aluminum replacement panels and roofing. When selecting new materials, prioritize light-colored finishes with a high Solar Reflectance Index (SRI); for low-slope roof surfaces, LEED recommends an SRI of 78 or higher.
The shelter should have lighting that meets the code requirements of the city or county and meets State Energy Code (Title 24). The SacRT design guidelines require lighting in and around light rail stations and bus stops and have a light level requirement. Where electricity is not available, the use of solar panels and battery storage should be used.
Occupancy sensors should be considered and may be required by code. Lighting at shelters should be adequate for public safety, low glare, easily maintained, and vandal resistance.
Advertising on shelters should be integrated into the overall shelter design versus being an afterthought. All advertising panels should be constructed from durable, vandal-resistant
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materials and positioned so they do not block airflow or trap heat within the shelter.
Advertisement signage should not dominate the aesthetic of the shelter and be scaled appropriately to the structure. Advertisement signs should not impede public safety of the shelter by reducing visibility.
Light Rail Station- Platform Structure
These structures have sides open to the greatest extent possible to allow ventilation and use perforated panels to maximize sun screening. The roof has a high Solar Reflective Index and is elevated high enough to reduce heat transmission to occupants.
Covered Walkway
This structure has sides open to the greatest extent possible to allow ventilation. The posts are located out of the walkway to the greatest extent possible and the roof has a high Solar Reflective Index and is elevated high enough to reduce heat transmission to occupants.
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Transit Center/ Pavilion
This structure has a large roof area with large spans between columns. The structure uses a roof form to allow ventilation through the roof and limit sun exposure. The roof has a high Solar Reflective Index and is elevated high enough to reduce heat transmission to occupants.
Best Practices for Shelter and Structure
The design of shelter and shade structures should prevent people from being able to climb them. Roof height should be kept above 10’. Avoid using posts that allow hand holds like a wide flange steel. Beams and braces should be kept at heights above 9’ to avoid climbing.
Other practices that can avoid climbing are post spacing greater than 42” apart, placing seating or low wall that can be used to access structure, and posts that have rough texture or groves that can be used hand holds. Post should be on a concrete base or made of reinforced concrete to greater durability and prevent base plates from rusting in standing water.
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Shade Structure Cost Estimate
Table 8. Cost estimates for various types of shade structures Shelter type:
Bus Shelter
5'x12'
Covered
Walkway
8'x50'
Light Rail
Structure
12'x50'
Pavilion/
Transit Center
30'x60'
Structure size (square
feet) 60 400 600 1,800
Shelter infrastructure
(per unit) $17,500.00 $44,000.00 $75,000.00 $207,000.00 Shelter labor $1,000.00 $12,000.00 $12,000.00 $15,000.00 Site material $1,500.00 $2,500.00 $5,000.00 $16,000.00 Site labor $5,500.00 $17,500.00 $17,500.00 $38,500.00
Total (per unit) $25,500.00 $76,000.00 $109,500.00 $276,500.00 Price per square foot $425.00 $190.00 $182.50 $153.61
Notes:
Cost estimate for the infrastructure (unit) does not include concrete pad construction, landscaping, drainage, lighting, and signage
Cost estimates assume bus shelter to be fully assembled when delivered to the shelter-ready site. Shelter labor is the cost to anchor the assembled structure to the foundation. New 6” concrete slab or pier footing would be constructed to accommodate a bus shelter.
Cost estimates for site material and site labor cover the materials and construction of a concrete pad and/or foundation for the structure.
Covered walkway, light rail structure, and pavilion are partially assembled and delivered to the site. Pier footing would be constructed on site for the structure.
Benefit-Cost Analysis
This section provides a hypothetical example illustrating a benefit-cost analysis (BCA) to evaluate the cost-effectiveness of installing a bus shelter in the city of Sacramento. The baseline scenario represents a typical bus stop without shelter, while the enhanced scenario considers adding a shelter to that bus stop.
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For the baseline scenario, only installation cost was considered that included bus stop materials, landing pad, and site labor of $325, $1,130, and $137, respectively, based on Utah Transit Authority (UTA)’s Bus Stop Master Plan adjusted to 2025 values (UTA, 2023).
For the enhanced scenario, the bus shelter infrastructure, shelter labor, site material, and site labor was taken from Table 8. Annual maintenance cost for the shelter beyond the baseline bus stop was assumed to be $109 (using the cost difference in maintaining bus stop with and without shelter from the City of Poway as a peer comparison).
The primary benefit of the bus shelter is its ability to provide shade and protection from the elements, making riders feel more comfortable during their wait time and retain riders on hot days. Therefore, the benefits considered in this analysis include perceived time savings and revenue loss reduction due to retention.
To quantify ridership retention, the daily individual trip rate was assumed to decrease by 27% on very hot days. This figure was estimated using the SacAdapt public survey results; 27% of regular transit riding respondents said that hot weather-related improvements would have a high impact (i.e., multiple times per week) on their mode choice. The annual number of very hot days was taken as 58, based on historical data from the vulnerability assessment report using where the Heat Index reached Extreme Caution or higher. Daily bus trips for a typical bus stop were calculated using SacRT data of 8.5 boarding trips per day on average across 2,766 bus stops without shelters. Considering a 27% reduction, a bus stop would lose 3 trips on each very hot day. Revenue was estimated at $1.20 per trip in 2025 (FTA, 2023). Hence, the retention benefit was to avoid annual revenue loss of $209 on very hot days at a bus shelter.
To monetize perceived time savings, Fan et al. (2016) found that waiting time at no-amenity bus stops was perceived as 1.3 times the actual waiting time, while perceived waiting time at bus shelters was close to actual. Assuming an actual waiting time of 18 minutes (half the average headway for Sacramento buses), the perceived time loss in the baseline case was 5.4 minutes. The value of time at transit waiting was taken as $40.20 per person per hour (USDOT, 2025). Using annual SacRT bus trips of 2,210 per bus stop, the annual value of perceived time saved at a bus shelter was estimated at $7,996, assuming 260 workdays to be conservative.
Using these benefits of the bus shelter and comparing them with the additional cost of the enhanced scenario beyond the baseline, the benefit-cost ratio was calculated. The lifecycle BCA spans 2025–2045 and applies a 7% discount rate, as recommended by USDOT (2025). In this analysis, Benefit-Cost Ratio (BCR) represents the ratio of total 66 | Page
monetized benefits to the additional costs of the enhanced scenario beyond the baseline.
A BCR greater than 1 indicates benefits exceed incremental costs.
Results are provided in Table 9.
Table 9. Summary of lifecycle costs and benefits for different scenarios Scenario
Costs ($) Benefits ($)
BCR Installation Maintenance Ridership
Retention
Time
Saving
Bus Stop
without
Shelter
1,592 -- -- -- --
Bus Stop
with Shelter 25,500 1,266 2,421 92,703 3.78
The main key takeaways of the assessment include:
• Shelter installation significantly increases lifecycle costs compared to a basic bus stop, primarily due to higher capital and replacement costs. • Maintenance costs for a shelter are only moderate.
• Benefits far outweigh costs for the enhanced scenario, with a Benefit-Cost Ratio (BCR) of 3.78, indicating strong cost-effectiveness.
• Largest benefit driver is perceived time savings, valued at $92,703 over the lifecycle, accounting for 97% of total benefits.
• Retention benefit contributes only 3% to the total benefits. • Shelters improve rider comfort and resilience, reducing vulnerability to extreme weather and supporting sustainability goals.
• Actual costs may vary depending on shelter design, materials, and site conditions.
Conclusion
The benefit-cost analysis indicates that installing bus shelters can be cost-effective. While initial capital costs are significantly higher than an unsheltered bus stop, the long-term benefits outweigh these costs under current assumptions. Additional benefits such as heat resilience and emission reductions further strengthen the case for deploying shelters.
Costs vary based on design, materials, and site conditions, which should be considered in planning. Bus shelters are most suitable in high-ridership or heat-vulnerable areas where enhanced amenities can improve transit rider experience and support sustainability goals. 67 | Page
References
Sacramento Regional Transit (SacRT): SacRT Bus and Light Rail Design Guidelines and Figures. Available at: https://www.sacrt.com/sacrts-bus-and-light-rail-design-guidelines- figures/
U.S. Green Building Council (USGBC): LEED Heat Island Reduction Credit Resources (cool roof / SRI guidance). Available at: https://www.usgbc.org/credits/new-construction-core- and-shell-schools-new-construction-retail-new-construction-data-cent-5 Meeting with Talor Manufacturing, 2025: Discussion on shelters.
LNI Custom Manufacturing, 2025: Discussion on shelters.
Brasso International, 2025: Discussion on shelters.
LandscapeForms and Studio 431, 2025: Discussion on shelters.
Utah Transit Authority (UTA), 2023: Bus Stop Master Plan. Available at:
https://www.rideuta.com/-/media/Files/About-
UTA/Reports/2023_BSMP_Compressed_a.pdf
City of Poway, 2023: Poway Road Corridor Study. Available at:
https://docs.poway.org/WebLink/DocView.aspx?dbid=1&id=170180&repo=CityofPoway& cr=1
Batur, I., Alhassan, V. O., Chester, M. V., Polzin, S. E., Chen, C., Bhat, C. R., & Pendyala, R.
M., 2024: Understanding how extreme heat impacts human activity-mobility and time use patterns. Transportation Research Part D: Transport and Environment, 136, 104431.
Federal Transit Administration (FTA), 2023: Annual Agency Profile — Sacramento Regional Transit District (NTD ID 90019). Available at:
https://www.transit.dot.gov/sites/fta.dot.gov/files/transit_agency_profile_doc/2023/90019 .pdf
Sacramento Regional Transit (SacRT), 2025: Annual Comprehensive Financial Report for the Fiscal Year Ended June 30, 2025. Available at: https://www.sacrt.com/wp- content/uploads/FY-2025-Annual-Comprehensive-Financial-Report.pdf
Brown, S., Cable, F., Chalmers, K., Clark, C., Jones, L., Kueber, G., and Yasukochi, E., 2006: Understanding how the built environment around TTA stops affects ridership: A study 68 | Page
for Triangle Transit Authority. PLAN 823 Fall Workshop, University of North Carolina, Chapel Hill.
Kim, J. Y., Bartholomew, K., and Ewing, R., 2018: Impacts of Bus Stop Improvements. Final report prepared for the Utah Department of Transportation Research Division, Report No.
UT-18.04, March 2018.
U.S. Environmental Protection Agency (EPA), 2025: GHG Emission Factors Hub. Available at: https://www.epa.gov/system/files/documents/2025-01/ghg-emission-factors-hub- 2025.pdf
Lesser, J. A., 2025: The social cost of carbon: A high-stakes, flawed metric. Energy Analytics. Available at: https://energyanalytics.org/the-social-cost-of-carbon-a-high- stakes-flawed-metric/
Fan, Y., Guthrie, A., and Levinson, D., 2016: Waiting time perceptions at transit stops and stations: Effects of basic amenities, gender, and security. Transportation Research Part A:
Policy and Practice, 88, 251–264.
U.S. Department of Transportation (USDOT), 2025: Benefit-Cost Analysis Guidance for Discretionary Grant Programs: 2026 Update (Final).
4.2 VEGETATION -BASED SHADING
Introduction
Sacramento’s hot-summer climate creates challenging conditions for people walking, biking and taking public transit. Increasing shade through trees is one of the most effective ways to reduce heat exposure and improve the comfort of bicycle and pedestrian facilities, and transit stops and stations. Trees provide natural cooling, improve comfort through evapotranspiration, and create shade that grows in effectiveness over time. In many locations, trees offer the most cost-effective and visually integrated long-term shading strategy.
This document provides planning-level guidance to help the City of Sacramento, SacRT, and partner jurisdictions integrate vegetation-based shading consistently and effectively across the city.
Purpose
The purpose of this document is to outline innovative strategies for underground support systems and maintaining shade trees in urban corridors. Guidance is focused on early 69 | Page
planning, not construction-level detail. Emphasis is placed on solutions that perform well under Sacramento’s heat conditions and can be maintained over time. For tree selection and placement, readers are referred to Sacramento Urban Forest Plan (City of Sacramento, 2024) as well as permits and ordinances from the City for up-to-date information.
Context
Many transit locations and urban corridors in Sacramento receive long hours of direct sun and have limited planting space due to utilities, narrow sidewalks, and paving. Because conditions and constraints vary widely, the strategies in this document are adaptable and intended for use across bus stops, light rail stations, transit centers, walkways, and public space improvements.
Water Establishment and Maintenance
Establishment Period
The tree establishment period is critical to achieving mature size and long-term health. For most trees, this means providing supplemental irrigation through the first two dry seasons and staking through the first two winters to protect against wind. A dry winter or hotter- than-normal summer may require additional watering. During establishment, watering frequency should gradually decrease while the amount of watering increases to encourage deep rooting. The goal is to develop an extensive root system capable of accessing water during drought conditions.
Water Requirements
Trees will require supplemental watering during the establishment period and, in some cases, beyond, depending on species-specific water needs. Drought-tolerant trees with well-established root systems can generally withstand the dry season with minimal stress.
During establishment, provide consistent irrigation through an automatic system or a structured weekly hand-watering schedule. Where permanent irrigation is not available, select low water use species appropriate to the region, using the Water Use Classification of Landscape Species (WUCOLS) database for guidance.
Irrigation Methods & Strategies
Newly planted trees will need additional water during the first 3 dry seasons. Apply water 2 to 3 times per week and monitor soil moisture to confirm it is reaching the root zone. Trees that are not drought tolerant will require permanent supplemental irrigation through the dry season. This water can be supplied by an automatic irrigation system or hand watering.
Automatic irrigation is the preferred method for both tree establishment and long-term watering. It requires a reliable water source and an electric irrigation controller that complies with all applicable state and local codes. Where conventional power is not available, a solar-powered controller may be used. Locate solar controllers away from the tree to avoid shading panel and position them for optimal sun exposure. 70 | Page
Where a permanent water source is not available, use a storage tank for tree watering. If electrical power is also unavailable, a solar-powered pump can be used to deliver water from the tank to the trees. Size the tank based on tree water demand and the anticipated frequency of refilling.
Irrigation should use low-flow emitters, generally at or below 15 gallons per hour (0.25 gallons per minute) per emitter. Place emitters near the tree root ball at installation and move them outward as the tree and root system expand. Install emitters and all related irrigation hardware where they are protected from vandalism, mowers, and regular foot traffic.
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For drought tolerant trees, hand watering may be used where automatic irrigation is not feasible. Water can be supplied from a quick coupler, hose bib, or water truck. Use a slow- release watering bag to make hand watering more efficient and to allow the soil to absorb water gradually. However, hand watering and watering bags come with challenges, including labor demands, potential vandalism, the need for removal and disposal at the end of use, and the risk that the bag will not last the full establishment period. When selecting a watering bag, consider water capacity, release rate, ease of filling, and durability. Note: Slow-release watering bags are most practical as a temporary establishment tool for a limited number of trees, especially in locations where permanent irrigation is delayed or not available, where access for trucks or hoses is available, and crews can reliably monitor, refill, and eventually remove the bags. They should not be relied on as the default long-term solution.
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Ongoing Tree Maintenance
Tree maintenance is required for the entire life of the tree. The level of maintenance will depend on species selection, placement, and the amount of soil volume provided.
Pruning is necessary to develop strong structure and reduce the risk of limb failure. For the first 10 years, trees should be pruned approximately every 2 years. After 10 years, a pruning cycle of about every 5 years is generally appropriate.
Tree stakes are to be removed after the second winter to allow the trunk to strengthen and to prevent damage as the tree outgrows the supports. During the establishment period, inspect stakes and ties regularly and repair or replace any damaged components to avoid rubbing, girdling, or instability.
Permanent irrigation serving newly planted trees should also be inspected regularly during the establishment period to ensure proper function and adequate watering. Once trees are established, irrigation checks can be reduced to monthly during the dry season, while still verifying that systems are functioning correctly and trees are not exhibiting stress.
Apply a layer of mulch in each tree planter to promote water retention, suppress weeds, moderate soil temperatures, and add organic matter as it breaks down. Use an organic mulch made from recycled or post-consumer materials where possible. Maintain a depth of 3 to 4 inches, keeping mulch pulled back from the root crown to prevent decay. Refresh or top up mulch every two to three years.
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Trees should be routinely monitored for overall health, including signs of drought stress, insect damage, fungal or bacterial infection, and vandalism. Maintenance staff should address issues promptly and use preventive practices to support long-term tree health.
Trees that have died or are unlikely to recover should be removed and replaced with a new tree. When possible, schedule new plantings between October and March, when establishment stress is reduced. After removal, the root crown or stump should be fully extracted or ground out to allow successful replanting.
Paving Around Trees and Underground Support Systems
Constraints & Overview
Urban areas and parking lots often have limited planter space for trees. Large planters may not be feasible because of paving, drive aisles, and walkways. In these situations, alternative approaches—such as suspended paving (soil-cell) systems or structural soil back-fill beneath pavement—can be used to increase rooting volume. These options add cost and come with design constraints, so they are most appropriate where traditional planters cannot provide enough soil for the desired tree size.
Traditional Tree Pits/Native Ground
Traditional tree pits use existing native soil without structural soil or soil-cell systems. They work best where planters are large enough for trees to mature—generally around 1,200 cubic feet or more—and where soils have not been heavily compacted or previously paved over.
In these conditions, trees can develop full canopies, roots can spread naturally, and long- term health is typically good. This is also the lowest-cost option, making it appropriate for corridors and sites that already have generous open-soil areas.
Where the tree planter soil was previously paved over or compacted, the entire planter should be amended by removing soil or tilling to a depth of 24”. Soils should be tested for fertility and amend per recommendation of soil fertility report.
Where planters are small and rooting volume is limited, traditional tree pits alone are unlikely to meet shade or longevity goals, and soil-cell systems should be considered.
Soil-Cell / Suspended Paving Overview
Suspended paving, also known as soil-cell systems, are modular structural frames— typically recycled-polypropylene lattices—installed beneath hardscape so pavement and vehicular loads are carried by the deck while trees grow in a protected rooting zone below.
The frames interlock to form work around utilities. The deck of the soil cell provides air and water to soil below paving. Planting soil is placed within the system in ≤12-inch lifts and lightly compacted to preserve porosity while controlling settlement. The upper 24 inches of the profile is an amended topsoil over screened structural fill, with all soils lab-tested before placement. Where stormwater treatment is part of the program, the fill may be a bioretention mix per the local LID manual. An underdrain system is recommended and 74 | Page
should be connected with storm drain system or use of a drywell where drain system is not available. A graded aggregate (gravel) base supports the modules and the approved pavement section. Soil cells are designed for a load rating of H20 and with some products the load rating can be increased. This allows vehicles to drive and park over the soil cells.
Graphic: GreenBlue Urban’s RootSpace soil-cell system providing structured soil volume and utility space beneath paving in a street tree application.
Soil-Cell Components
A typical soil-cell assembly includes:
1. Prepared subgrade with geotextile and/or aggregate base per the approved pavement section.
2. Modular cell frames (polypropylene lattice modules) stacked to design depth with interlocks/connectors and load-spreading lids/decks engineered to the project’s load rating. Manufacturers of soils cells include Deep Root Silva Cell, GreenBlude Urban RootSpace, and Citygreen Stratacell.
3. Utility corridors/sleeves routed through the matrix to keep conduits serviceable.
4. A manufacturer specified top soil placed in ≤12-inch lifts inside the cells with light compaction.
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5. Aeration/inspection inlets at the surface for gas exchange, moisture checks, and maintenance access.
6. Drip irrigation both in planter and under pavement using perforated pipe and serviceable access point on ends.
7. Recommend perforated drainpipe connection to storm drain or drywell.
8. Root-management barriers at hardscape edges/utilities to encourage root growth into the vault.
9. Edge restraints curbs or root management barrier at pavement section.
10. The tree opening with mulch in planter.
Graphic: DeepRoot Silva Cell system showing how stormwater is captured and stored in structured soil beneath pavement to support a large street tree.
Targeted Soil Volume for Soil-Cells
Tree performance tracks closely with soil volume. As a planning target, provide about 1,200 cubic feet per large shade tree, or about 400 square feet and 3 feet of soil depth. This typically supports a large canopy under urban conditions (species dependent). Linking tree planters and allowing roots to share space can help reduce total required soil volume. Soil cell manufacturers may have additional guidance for soil volume sizing.
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Soil-Cell Backfill
Use a loam-based planting topsoil with organic matter and a controlled fraction of fines (silt and clay) to balance structure, moisture retention, and aeration. Lab-test each source for texture, organic matter, pH, EC/salts, and nutrients. Place backfill in lifts no thicker than 12 inches, lightly compacted by foot in each cell, and use limited water to help settle soil into cells. During placement, protect porosity by not working soil when wet. Soil compaction should not exceed 85% compaction. Keep fertility data-driven: add compost or targeted amendments only when lab results call for it, and re-test if sources change. If soil cells are greater than 30” deep, then a fill soil layer should be used below 30”. The screened fill soil should have less than 5% organics and be compacted using the same methods as the topsoil. Soil cell manufacturers will provide soil specifications that best support their product ability to grow healthy trees.
Soil-Cell Irrigation and Aeration Methods
Provide a dedicated low-flow drip zone for the soil-cell area so flow, runtime, and scheduling can be controlled independently from surrounding landscape planting. Use pressure-regulated valves with filtration at each control zone, and do not tie soil-cell trees to turf or spray irrigation programs. Route mainline and lateral piping through designated utility corridors within or just below the soil-cell layout so lines stay accessible and do not displace planting soil. From these corridors, run distribution tubing to each tree opening.
Place emitters or dripline at the top of the root ball and across the soil-cell zone where roots are expected to develop. Provide surface aeration/inspection inlets at appropriate locations so air can move in and out of the vault and maintenance staff can check moisture, flush lines, and observe performance. When irrigating trees, make sure to use deep irrigation with infrequent watering cycles that wet the full soil-cell profile and encourage deep rooting for trees.
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Graphic: Soil-cell irrigation and aeration layout showing drip tubing looped through the vault, a drip ring at the tree root ball, and a surface grate for inspection and maintenance.
Root Barriers at Pavement and Utilities
Use linear root-barriers that are 30” deep where pavements, utilities, walls, or foundations need protection. Place root-barriers at paving edges to guide roots down into the soil-cell system instead of outward beneath the paving profile. Keep the rooting zone inside the soil-cell field as continuous as possible, and avoid ringing the tree or segmenting the internal soil volume with unnecessary barriers unless protecting a utility or other elements that need protection from roots.
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5| BIKE/PEDESTRIAN BRIDGE
INSPECTIONS
5.1 PURPOSE
Bike/pedestrian bridges are typically lighter structures than vehicular bridges and often include unique features such as timber decks, handrails, and architectural elements.
Inspections ensure public safety, structural integrity, and user comfort, while also accounting for non-vehicular load types, vandalism or misuse.
5.2 INSPECTION FREQUENCY
Type of Inspection Frequency Notes
Initial (Baseline) After construction completion Establish baseline condition
Routine Inspection Every 24 months (2 years)
Shorter intervals (12
months) may be
recommended for timber or
corrosion-prone materials
Special Inspection As needed (after flood, impact, fire, vandalism, or seismic event) Focused on affected areas In-Depth Inspection Every 4–6 years or when
deterioration is suspected Hands-on, detailed
Fracture-Critical
Inspection Every 24 months, if applicable
For non-redundant
members in steel truss or
tied-arch systems
Underwater Inspection
Every 5 years, if applicable or as
needed after flood events if there has
been visible damage above water
from vessel impact, or build-up of
debris at piers or abutments
For bridges located in deep
water ways
Note: Pedestrian bridges owned by cities or parks departments may follow less formal schedules, but documentation and consistency are key.
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5.3 INSPECTION CHECKLIST
A. General Information
• Bridge name, bridge number, location and owner
• Bridge type and material (steel, concrete, timber, aluminum, composite) • Span configuration and support type
• Foundation and abutments type
• Year built / last rehab / last modification
• Load rating (if available)
• Deck width and ADA compliance
B. Approach and Site Conditions
Item What to Look For Notes
Approaches Settlement, erosion, alignment issues Trip hazards or abrupt grade changes
Drainage Clogged inlets, ponding, undermining Standing water accelerates decay Vegetation Overgrowth, root intrusion, visibility
issues Can hide defects or damage
Embankments Erosion, scour, slope stability Particularly after storms or flooding
C. Substructure (Abutments, Piers, Footings)
Item What to Look For Notes
Concrete Cracking, spalling, delamination Check near joints and base Steel Corrosion, section loss, loose
connections Pay attention to anchor bolts
Timber Rot, insect damage, fastener
loosening Probe suspect areas
Foundations Scour, settlement, undermining Verify bearing alignment
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D. Superstructure (Main Load-Carrying Elements)
Item What to Look For Notes
Girders /
Trusses
Cracks, corrosion,
deformation, unsound concrete, voids,
honeycombing
Fatigue-prone areas at welds
Connections Bolt tightness, weld quality, rust Watch for vandalism or missing hardware
Bearings Movement, corrosion, frozen
condition Often overlooked in small bridges
E. Deck System
Item What to Look For Notes
Deck Surface Cracks, delamination, potholes,
unevenness, unsound concrete, voids
Evaluate for ADA compliance and
tripping hazards
Deck Material Timber decay, delamination (FRP),
corrosion (metal) Non-slip surface condition
Drainage Blocked scuppers or trapped moisture Important for long-term durability
F. Rails, Barriers, and Fencing
Item What to Look For Notes
Railings /
Handrails
Loose, bent, corroded, missing
elements or non-compliant height User safety concern
Fencing /
Screens Vandalism, damage, sharp edges Especially on overpasses Connections Missing bolts, weld cracks Critical to fall prevention
G. Lighting, Signage, and Accessories
Item What to Look For Notes
Lighting Functionality, wiring damage,
vandalism Ensure safety for nighttime users
Signage Missing, faded, or incorrect Include clearance and load limit signs
Utilities Exposed conduit, leaks,
missing/damaged utility covers
Especially if combined with lighting
cables
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Striping / Markings
on Deck Surface
Check for peeling or fading,
missing markings Encourage safe use
H. Surface / User Experience
Item What to Look For Notes
Skid
Resistance Worn surface, algae/moss growth Common hazard on timber or composite decks
Expansion
Joints
Gaps, misalignment, debris,
missing covers or seals Can trip pedestrians or cyclists ADA
Compliance
Slopes, surface smoothness,
detectable warnings
Evaluate per PROWAG/ADA
standards
I. Environmental and Aesthetic Elements
Item What to Look For Notes
Coatings /
Paint Peeling, fading, corrosion underneath Preventive maintenance indicator Drainage
Systems Leaks, plugged drains Accelerates structural decay Landscaping
/ Context Root intrusion, visibility Important for safety perception
J. Documentation and Photos
• Take photos or video of all structural members and any noted defects • Record dimensions, crack widths, corrosion depth, etc. • Note vandalism or graffiti that could conceal defects
5.4 KEY DIFFERENCES FROM VEHICULAR BRIDGE
INSPECTIONS
Aspect Bike/Pedestrian Bridge Focus Vehicular Bridge Focus Loads Pedestrian, cyclist, maintenance vehicle
(light loads) Heavy vehicular loads
Deck Materials Concrete, timber, composite, aluminum,
FRP common Concrete, steel typical
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User Safety Handrails, slip resistance, ADA
compliance
Guardrails, vehicle
impact protection
Frequency Often similar (every 2 years) but may vary
by ownership
FHWA-mandated (every
2 years for NBI)
Vandalism Risk Higher—fencing, lighting, graffiti Lower priority Aesthetic /
Architectural
Features
Often integral to design Secondary
Dynamic Effects Vibration and comfort for pedestrians Fatigue and heavy live loads
5.5 REFERENCES AND STANDARDS
• FHWA Bridge Inspection Reference Manual (2024)
• NBIS (23 CFR 650 Subpart C) — National Bridge Inspection Standards • AASHTO LRFD Guide Specifications for Design of Pedestrian Bridges (2nd Ed.) • FHWA-HRT-05-130: Pedestrian Bridge Inspection Guide
• Manual for Bridge Evaluation (AASHTO)
• ADA / PROWAG Guidelines for accessibility
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6| CNG INFRASTRUCTURE
6.1 OVERVIEW
Sacramento Regional Transit District (SacRT)’s fueling infrastructure relies on compressed natural gas (CNG) compressors supported by a programmable logic controller (PLC)- based control system and supervisory control and data acquisition (SCADA) for automation and monitoring. The compressors are designed to deliver high throughput fueling for transit fleets, operating in parallel to provide redundancy and meet peak demand. The PLC system coordinates compressor sequencing, storage bank management, and dispenser operations, while SCADA provides system-wide visibility, logging, and remote monitoring of pressures, flows, alarms, and operational status.
However, the current equipment and control systems present significant challenges. The three Gemini compressors in operation are past their useful life, and sourcing parts have become increasingly difficult due to reliance on a single distributor. As these compressors age, maintenance costs continue to rise, creating financial and operational strain.
Additionally, the existing PLC and SCADA systems are outdated and do not provide comprehensive sensor data, limiting the ability to detect issues early and implement predictive maintenance strategies. This reactive approach increases the risk of major faults and unplanned downtime.
Climate conditions further compound these issues. During summer months, compressors run hotter, and the lack of adequate cooling leads to a higher likelihood of high-heat faults.
These faults occur more frequently in summer than in winter, disrupting fueling operations and increasing maintenance demands. As conditions continue to get hotter, disruptions are expected to increase. Together, aging equipment, outdated controls, and seasonal stressors pose a growing risk to reliability, safety, and operational efficiency.
6.2 BENEFITS OF MODERNIZATION
Upgrading aging compressors and PLC systems delivers significant operational and resilience benefits:
• Improved Reliability: Modern compressors combined with advanced PLC and monitoring systems enable real-time diagnostics and condition monitoring that support proactive maintenance and reduce unplanned outages. Federal research has shown that diagnostics- and prognostics-based maintenance strategies improve equipment availability and reduce downtime by allowing faults to be identified and addressed before failure occurs, extending overall asset life and improving maintenance planning (NIST, 2020; NIST, 2024). • Enhanced Safety: Modernized control architectures with integrated sensors, alarms, and supervisory monitoring improve early detection of abnormal operating 84 | Page
conditions and support automatic placement of the system into a safe state. For CNG fueling facilities, safety codes explicitly require gas detection systems to initiate compressor shutdown and stop gas flow, with manual verification required before restart, demonstrating the critical role of updated controls and safety logic in preventing escalation and catastrophic failures (NFPA, 2022). • Energy Efficiency: Optimized sequencing and load management are widely recognized as energy-efficiency measures. DOE guidance identifies control systems as a critical determinant of overall compressor energy performance and recommends quantifying energy and cost savings achieved through improvements in control logic and operational strategies (DOE, 2003). • Climate Resilience: Resilience improvements include specifying control panels and components rated for ambient temperatures above the common 40 °C (104 °F) baseline, unless explicitly marked otherwise, and deploying control and monitoring systems to detect abnormal conditions and enable rapid, safe recovery. Elevated temperatures are widely recognized to accelerate failure mechanisms through Arrhenius-type behavior (NIST, 2023), underscoring the importance of heat mitigation strategies and appropriate component ratings.
6.3 REPLACEMENT STRATEGY
• Full-System Replacement: Recommended when compressors and controls are past their useful life or incompatible with modern PLC and SCADA platforms. This approach ensures uniform technology, reduces lifecycle costs, and simplifies maintenance.
• Piecemeal Upgrades: Lower upfront cost but may lead to integration challenges, uneven performance, and higher long-term maintenance expenses. Retrofit kits can offer short-term relief but often lack full compatibility with advanced monitoring and sequencing features.
Given SacRT’s aging compressors, limited parts availability, and outdated SCADA system, a full-system modernization may be the most cost-effective and resilience-focused option.
6.4 RESILIENCE AND A DAPTATION MEASURES
CNG fueling facilities that support transit fleets face growing exposure to climate-driven stressors such as extreme heat, flooding, and power disruptions. Integrating resilience and adaptation measures into compressor systems and PLC-based controls is essential to maintain fueling reliability and protect fleet availability under current and future climate conditions.
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Extreme Heat and Thermal Stress
High ambient temperatures reduce compressor efficiency, elevate discharge temperatures, and accelerate wear on seals, lubricants, and electronic components. Heat stress also impacts PLC panels, variable frequency drives (VFDs), and communication hardware, increasing the likelihood of nuisance trips or premature failures. Heat mitigation options include:
• Shaded or enclosed compressor skids, along with noncombustible canopy structures, can reduce surface temperatures by 15–45°F (UNH, 2024; Al Tahir et al., 2025), lowering thermal stress on compressors and electrical panels. Ensure the material is appropriately fire-rated and that it is designed in a way to prevent build- up of ignitable vapors.
• Enhanced ventilation, high-temperature-rated electrical components, and control logic that modulates compressor loading during peak heat conditions further improve resilience.
• Adaptive PLC sequencing—such as rotating lead compressors or limiting simultaneous starts—reduces thermal stress while maintaining fueling throughput.
Flooding, Stormwater, and Site Conditions
Flooding and inadequate drainage can damage compressors, electrical panels, and underground piping, particularly at older facilities not designed for intense precipitation.
Adaptation measures include elevating critical equipment above projected flood levels, sealing conduit penetrations, and incorporating flood sensors tied to PLC alarms (EPA, 2015). Early detection and controlled shutdowns reduce the risk of catastrophic equipment damage and extended fueling outages.
Power Reliability and Grid Disruptions
CNG stations are highly dependent on grid power for compressors, dryers, controls, and dispensers. Extreme weather events underscore the vulnerability of fueling infrastructure to prolonged outages. Resilience strategies include integrating backup generation or microgrids, prioritizing critical loads within PLC logic, and implementing controlled shutdown/startup sequences to prevent equipment damage during power loss and restoration. PLC-based monitoring and alarms accelerate recovery by identifying system states and faults after outages.
Role of PLC and SCADA in Adaptive Operations
PLC and SCADA systems are central to climate resilience, enabling condition-based operations rather than fixed schedules. Temperature and pressure trends, runtime, and fault data supports predictive maintenance and informed operational decisions during extreme events. When integrated with agency emergency response plans, these systems help ensure fueling capacity aligns with service priorities during climate-driven disruptions. 86 | Page
6.5 BENEFIT -COST CONSIDERATIONS
At the planning level, climate-resilient upgrades to CNG compressor and PLC systems can be assessed through a benefit–cost analysis that weighs incremental capital and operating costs against avoided service disruptions, reduced equipment damage, and faster recovery during extreme events. Benefits are typically monetized through avoided fuel- supply outages (e.g., missed trips or bus pull-outs), emergency repairs, premature equipment replacement, and reduced labor or contractor costs, as well as avoided safety incidents (USDOT, 2025). Additional advantages include lower energy consumption from optimized compressor sequencing and load management, and reduced risk of prolonged fleet downtime during heat waves, flooding, or power outages. Federal guidance recommends using probabilistic hazard exposure, expected annual damage reduction, and avoided downtime metrics to quantify these benefits at a screening level, especially when detailed failure data are limited (Filosa, 2017). For transit fueling infrastructure, even modest reductions in outage frequency or duration can yield favorable benefit–cost ratios given the high operational and societal costs of lost transit service during extreme weather events.
6.6 CONCLUSION
SacRT’s aging compressors and outdated PLC/SCADA systems pose growing risks to system reliability, safety, and cost efficiency. Rising maintenance demands, limited diagnostics, and seasonal heat-related faults highlight the need for modernization.
Upgrading to modern compressors and advanced control systems will improve reliability through predictive maintenance, enhance safety with integrated monitoring, and boost energy efficiency. A full-system replacement may be the most cost-effective, long-term solution—reducing lifecycle costs, simplifying maintenance, and ensuring operational resilience to support SacRT’s transit service under evolving conditions.
References
National Institute of Standards and Technology (NIST), 2020: Economics of Manufacturing Machinery Maintenance: Survey and Analysis of U.S. Costs and Benefits. NIST:
Gaithersburg, MD, USA.
National Institute of Standards and Technology (NIST), 2024: Monitoring, Diagnostics, and Prognostics for Manufacturing Operations. NIST: Gaithersburg, MD, USA.
National Fire Protection Association (NFPA), 2022: NFPA 52 – Vehicular Gaseous Fuel Systems Code. NFPA: Quincy, MA, USA.
87 | Page
U.S. Department of Energy (DOE), 2003: Improving Compressed Air System Performance:
A Sourcebook for Industry. DOE Office of Energy Efficiency and Renewable Energy:
Washington, D.C., USA.
National Institute of Standards and Technology (NIST), 2023: Arrhenius Equation and Temperature Acceleration Models. NIST/SEMATECH e-Handbook of Statistical Methods:
Gaithersburg, MD, USA.
UNH, 2024: Shade Matters. University of New Hampshire Extension: Durham, NH, USA.
Al Tahir, I., Abd El Fattah, A., Mohammed, M., Asif, M., & Almahdy, O., 2025: Thermal performance and shading strategies for outdoor infrastructure. Building and Environment.
Elsevier: Amsterdam, Netherlands.
U.S. Environmental Protection Agency (EPA), 2015: Flood Resilience: A Basic Guide for Water and Wastewater Utilities. EPA: Washington, D.C., USA.
U.S. Department of Transportation (USDOT), 2025: Benefit-Cost Analysis Guidance 2025 Update II (Final).
Filosa, G., 2017: FHWA’s Vulnerability Assessment and Adaptation Framework, 3rd Edition. Bureau of Transportation Statistics: Washington, D.C., USA.
7| SACRT LIGHT RAIL TRACTION
POWER SUBSTATION HVAC
EQUIPMENT
7.1 SUMMARY
SacRT’s existing Impulse Substations are responsible for powering the light rail system.
These substations are considered mission critical sites and require a myriad of support systems to operate properly. One of these support systems is the Heating, Ventilation, and Air Conditioning (HVAC) system. HVAC systems are vital to prevent substation overheating and condensation, and to reduce dust infiltration and accumulation of dangerous gases. A properly maintained and designed HVAC system is necessary for reducing service downtimes, improving electrical equipment efficiency, mitigating risks to mission critical equipment, and protecting SacRT staff. Over time, HVAC equipment does need to be replaced as it reaches the end of its useful life.
Due to high temperature alarms occurring at many of the existing substations, a site inspection was performed on one of the substations – Y2 – to investigate the HVAC equipment. The substation visited is a standalone building that has dimensions, construction, electrical equipment, and HVAC equipment typical of substations used by SacRT. Each of these substations has two outdoor pad-mounted air handler units and two indoor wall-mounted air handling units with ductwork installed.
7.2 CONDITION OF EXISTING HVAC EQUIPMENT
During the site visit the following observations were made:
• SacRT staff confirmed that overheating has occurred at many of the substations, which results in the substation going offline.
• SacRT staff mentioned that it appears that HVAC equipment is undersized at most locations.
• Some HVAC equipment at other sites was not functional or had reduced functionality.
• Equipment was not working at many other sites causing significant temperature issues.
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• Hydrogen ventilation equipment was not present and presents a hazardous condition if left unmonitored.
• The existing HVAC equipment does not have the ability to pressurize the substation nor use an economizing cycle. Typically, these spaces are pressurized to prevent dust from building up on the equipment. Economizing is also important to improve the overall efficiency of the system.
• Air filters were missing or were not properly secured. There were no visible means/devices to properly secure the filters.
Table 10. Existing HVAC Equipment Table at Y2 Substation Unit /
Location
Manf. Model Capacity
(Btu/h)
Voltage/
Phase
Conditio
n
Refrigeran
t
Year
Installe
d
Condenser #1
/ Outside
Bryant 105ANA060 60,000 230/1 Near End
of Life
R410A -
Air Handling
Unit #1 /
Indoor
Carrier FB4CNP061 60,000 230/1 Near End
of Life
R410A 2015
Condenser #2
/ Outside
American
Standard
5A7A5060A-
1000AA
60,000 230/1 Good R454B 2024
Air Handling
Unit #2 /
Indoor
Trane 5TEM6D07-
AV51SAA
60,000 230/1 Good R454B 2025
Note: The data above regarding HVAC capacity was taken from manufacturer cut sheets for the equipment model number.
An inventory of the equipment was developed (see Table 11) to help assess whether the existing HVAC system may be undersized. Because the actual heat output of the traction power substation equipment is not available, a rough order of magnitude comparison was used. This value does not include envelope or lighting loads. A definitive conclusion cannot be reached until a detailed heating and cooling load calculation is performed. However, this assessment suggests that the HVAC equipment is undersized, particularly considering the existing substations have older equipment that is less efficient than modern electrical equipment.
This rough estimate was compared to a substation for a similar light rail system with similar building dimensions and equipment capacities. The more detailed heating and cooling load analysis for the comparable facility indicated equipment heat generation slightly above 77,000 Btu/hr, still significantly exceeding the capacity of the existing HVAC 90 | Page
system. The estimated total heat gain value for Y2 is significantly higher than what has been seen on other projects, but this may be due to the estimated value being based on average of electrical equipment as opposed to what the actual loading of existing traction power.
Table 11. Y2 Substation-Electrical Equipment Table
Equipment Qty Nameplate Data Estimated Heat Gain
Each (btu/hr)
Notes
Rectifier & Transformer 1 2250 kVA 56,000 1
Auxiliary Power Transformer 25 kVA 2,900 1
Positive and Negative
Disconnect Switch
1 4000 A 12,600 2
DC Negative Bus 1 4000 A 1400 1
DC Positive Bus 1 4000 A 1400 1
DC Panel Board 1 125 V 1000 2
DC Feeder Beaker 2 4000 A 12,600 2
Battery Rack 1 Negligible 3
Battery Charger 1 200 A 4,900 1
AC & DC Circuit Breaker 1 1200 A 2,000 2
AC Distribution Panel Board 1 1,000 2
TOTAL 108,400
Note 1: Estimated Heat Gain Range values are obtained by interpolating between values found in tables from ASHRAE RP-1104 “Heat Loss from Electrical and Control Equipment in Industrial Plants: Part ll -Results and Comparisons”. Assumed an 80 percent loading factor of rated capacity.
Note 2: Data taken from Eaton “Power Distribution Systems Typical Components of a Power System”. This data includes typical heat gain values for electrical equipment.
Note 3: The worst-case scenario for a battery rack and charger system is when the system is charging and in this case the battery rack’s heat generation is negligible.
7.3 RECOMMENDATIONS FOR SUBSTATION HVAC
EQUIPMENT
The most critical issue identified is the recurring high temperature alarms within the traction power substations, caused by elevated internal temperatures. If these conditions persist, they may lead to service disruptions and potential electrical equipment failures.
Addressing this concern will require corrective actions to the existing HVAC systems, including replacement of failed components and evaluation of equipment that may be undersized for the current heat loads.
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Two potential approaches are available; however, based on observed conditions, staff input, and experience on similar substation projects, Option 1 is strongly recommended.
Option 1 – Comprehensive Load Analysis and Engineered HVAC Replacement (Recommended)
Based on input from SacRT staff and WSP experience with comparable traction power substations, the existing HVAC systems could be undersized for current operating conditions. As such, it is recommended that a detailed heating and cooling load calculation be performed prior to implementing corrective measures. This analysis would quantify actual thermal loads driven by electrical equipment, occupancy, ventilation, and envelope conditions, and would establish the true capacity requirements for reliable substation operation.
Simply replacing failed HVAC units on a like-for-like basis does not address the underlying risk and does not guarantee prevention of future overheating events. If the load analysis confirms that higher-capacity systems are required, the recommended approach is to proceed with a fully engineered HVAC system design tailored to each substation’s operational needs. This approach ensures that replacement equipment is appropriately sized, code-compliant, energy-efficient, and capable of maintaining continuous operation under worst case conditions.
Option 1 addresses both immediate reliability concerns and long-term system performance, significantly reducing the risk of recurring shutdowns and unplanned outages.
Option 2 – Reactive Testing and Incremental Replacement (Not Recommended) Under Option 2, no formal load calculations would be performed. Instead, substations that have experienced high-temperature alarms would receive individual site visits to evaluate HVAC unit performance. This process would include filter replacement, equipment cleaning, refrigerant verification per manufacturer's recommendations, and performance retesting. Units that continue to underperform after maintenance would then be replaced through the standard procurement process.
While Option 2 may resolve isolated equipment failures, it is inherently reactive and does not evaluate whether a systemic capacity deficiency exists across the substation portfolio.
As a result, this approach carries a higher risk that overheating events will persist even after equipment replacement. For this reason, Option 2 is considered inferior to Option 1 and does not provide the same level of operational certainty. 92 | Page
Additional System Recommendations (Applicable Regardless of Selected Option) Regardless of the selected path for addressing immediate HVAC deficiencies, the following improvements are recommended to enhance safety, reliability, and maintainability of substation HVAC systems:
• Dedicated Battery Exhaust System: Provide a dedicated exhaust system for battery rooms to mitigate the risk of hydrogen gas accumulation associated with lead acid batteries. This system is required by current building codes for battery-equipped spaces. Existing wall penetrations may be repurposed; however, engineering design will be required to ensure proper airflow rates, controls, and code compliance. • Return Plenum and Controlled Outside Air Intake: Add a return plenum to indoor air- handling units, including a return grille, filter section, access door, ducted outside air intake, and motorized outside air control damper. This configuration would improve filter maintenance, enable controlled ventilation, and allow the substation to be slightly pressurized to limit dust infiltration. This enhancement would be naturally incorporated as part of the engineered solution developed under Option 1.
7.4 CONCLUSION
The assessment of the Y2 traction power substation indicates that recurring high temperature alarms are likely linked to deficiencies in the existing HVAC systems, including aging equipment, lack of proper ventilation features, and the potential for undersized cooling capacity relative to current electrical loads. While preliminary analysis suggests that the existing HVAC equipment may be insufficient, a definitive determination requires a detailed heating and cooling load calculation. Addressing these issues is essential to maintaining reliable substation operation, preventing service disruptions, and protecting mission critical electrical infrastructure. Implementing a comprehensive, engineered HVAC replacement supported by formal load analysis offers the most effective long-term solution. Regardless of the selected approach, additional improvements such as dedicated battery exhaust, controlled outside air intake, and proper filtration will enhance safety, performance, and maintainability across SacRT’s substation network.