research report

Life Cycle Assessment of Environmental and Economic Impacts of Deploying Alternative Urban Bus Powertrain Technologies in the South Coast Air Basin

Publication Date

May 9, 2022

Associated Project(s)

Author(s)

Analy Castillo Munoz, Brian Tarroja, Scott Samuelsen

Areas of Expertise

Freight, Logistics, & Supply Chain Public Transit, Shared Mobility, & Active Transportation Safety, Public Health, & Mobility Justice

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Abstract

To aid in addressing issues of air quality and greenhouse gas (GHG) emissions in the South Coast Air Basin, local transit agencies are considering a shift to battery electric buses (BEBs) and hydrogen fuel cell electric buses (FCEBs). Each of these options varies in their overall effectiveness in reducing different emission types over their life cycle, associated life cycle costs, ability to meet operational needs of transit agencies, and life cycle environmental footprint. This project carried out a lifecycle-based analysis and comparison of the GHG emissions, criteria pollutant emissions, and other environmental externalities associated with BEBs and FCEBs, taking into account their ability to meet the operational constraints of the Orange County Transportation Authority. From an environmental footprint perspective, this study found the following. First, both FCEBs and long-range BEBs have comparable impacts on global warming potential and particulate matter formation but when the FCEBs were fueled using renewable hydrogen. Second, using electricity from the current California grid mix to drive electrolysis to produce hydrogen for FCEBs produced only marginal benefits compared to current natural-gas-fueled vehicles due to the low supply chain efficiency of this pathway. Third, the mining of precious metals is a major contributor to environmental footprint categories for both BEBs and FCEBs. Fourth, both FCEVs and long-range BEBs provide significant reductions in environmental footprint compared to conventional diesel and natural gas buses. From a cost perspective, this study found the following. First, with current-day cost inputs, FCEBs and BEBs have comparable total costs of ownership, but both have slightly higher costs than diesel and natural gas buses. Second, FCEBs have an equivalent total cost of ownership to BEBs when the electricity rate for charging is $0.24/kWh. Higher values render FCEBs as the cheaper option and lower values render BEBs as the cheaper option. Second, the total cost of ownership of these technologies is highly sensitive to electricity costs, and the rapid evolution of the electricity system has strong implications for the economic comparison between BEBs and FCEBs. Overall, this study finds that while both FCEBs and BEBs provide life-cycle environmental benefits, further cost reductions in electricity rates and initial purchase costs are needed to achieve total cost of ownership parity with conventional bus powertrains. With the rapid evolution of the electricity system and falling costs for renewable electricity resources, these cost reductions may occur in the near future.

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policy brief

Electrified Buses Provide Life Cycle Environmental Benefits but Need Cost Reductions and Policy Support for Near-Term Adoption

research report

How to Evaluate and Minimize the Risk of COVID-19 Transmission within Public Transportation Systems

Publication Date

May 2, 2022

Associated Project(s)

How to Evaluate and Minimize the Risk of COVID-19 Transmission within Public Transportation Systems

Author(s)

Yiduo Huang, Max Shen

Areas of Expertise

Public Transit, Shared Mobility, & Active Transportation Safety, Public Health, & Mobility Justice

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Abstract

During the COVID-19 outbreak, serious concerns were raised over the risk of spreading the infection on public transportation systems. As the pandemic recedes it will be important to determine optimal timetable design to minimize the risk of new infections as systems resume full service. In this study, the research team developed an integrated optimization model for service line reopening plans and timetable design. The model combines a space-time passenger network flow problem and compartmental epidemiological models for each vehicle and platform in the transit system. The algorithm can help policymakers to design schedules under COVID-19 more efficiently. The report develops an optimized timetable for the Bay Area Rapid Transit system. The team found that if passengers choose other modes of transportation when closing part of the system or decreasing the frequency of service can prevent the spread of infections, otherwise, if passengers choose to use the closest open station, closings will lead to longer waiting times, higher passenger density and greater infection risk. The researchers found that the goal of stopping the spread of infection could be achieved by minimizing the total delay when infections were similar in different districts across the service area. Where infection rates are different in different districts, minimizing the risk of exposure can be achieved by minimizing weighted travel time where higher weights are applied to areas where the infection rate is highest.

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policy brief

How Might Adjustments to Public Transit Operations Affect COVID-19 Transmission?

research report

Using Automated Vehicle (AV) Technology to Smooth Traffic Flow and Reduce Greenhouse Gas Emissions

Publication Date

May 3, 2022

Associated Project(s)

Using Automated Vehicle (AV) Technology to Smooth Traffic Flow and Reduce Greenhouse Gas Emissions

Author(s)

Daniel Rothchild, Kanaad Parvate, Sulaiman Almatrudi, Upadhi Vijay

Areas of Expertise

Infrastructure Delivery, Operations, & Resilience Intelligent Transportation Systems, Emerging Technologies, & Big Data

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Abstract

Passenger and heavy-duty vehicles make up 36% of California’s greenhouse gas (GHG) emissions. Reducing emissions from vehicular travel is therefore paramount for any path towards carbon neutrality. Efforts to reduce GHGs by encouraging mode shift or increasing vehicle efficiency are and will continue to be, a critical part of decarbonizing the transportation sector. Emerging technologies are creating an opportunity to reduce GHGs. Human driving behaviors in congested traffic have been shown to create stop-and-go waves. When waves form, cars periodically slow down (sometimes to a stop) and then speed back up again; this repeated braking and accelerating leads to higher fuel consumption, and correspondingly increasing GHG emissions. Flow smoothing, or the use of specially designed adaptive cruise controllers to dissipate these waves, can reduce the fuel consumption of all the cars on the road. By keeping all vehicles at a constant speed, flow smoothing can minimize system-wide GHG emissions. This report presents the results of flow smoothing when used in simulation, discusses current work on implementing flow smoothing in real highways, and presents policy discussions on how to support flow smoothing.

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policy brief

Automated Vehicle Technology Has the Potential to Smooth Traffic Flow and Reduce Greenhouse Gas Emissions

policy brief

How Might Adjustments to Public Transit Operations Affect COVID-19 Transmission?

Publication Date

April 28, 2022

Associated Project(s)

How to Evaluate and Minimize the Risk of COVID-19 Transmission within Public Transportation Systems

Author(s)

Yiduo Huang, Max Shen

Areas of Expertise

Public Transit, Shared Mobility, & Active Transportation Safety, Public Health, & Mobility Justice

View policy brief

Abstract

During the COVID-19 pandemic, public transportation systems worldwide faced many challenges, including significant loss of ridership. Public agencies implemented various COVID-19-related policies to reduce transmission, such as reducing service frequency and network coverage of public transportation. Recent studies have examined the effectiveness of these policies but reach different conclusions due to varying assumptions about how passengers may react to service changes.

Related Publications

research report

How to Evaluate and Minimize the Risk of COVID-19 Transmission within Public Transportation Systems

policy brief

Refueling Behavior of California Fuel Cell Vehicle Drivers

Publication Date

April 22, 2022

Associated Project(s)

Identifying Gaps in California’s Hydrogen Fueling Station Network through an Assessment of the Refueling Behavior of Fuel Cell Vehicle Drivers

Author(s)

Adam Davis, Gil Tal, Scott Hardman

Areas of Expertise

Zero-Emission Vehicles & Low-Carbon Fuels

View policy brief

Abstract

California has a goal of reaching 100% zero emission vehicle (ZEV) sales by 2035. Most ZEV sales to date have been plug-in electric vehicles, with fuel cell electric vehicles (FCEVs) making up only around 1% of ZEV sales. The market for FCEVs may be constrained because, unlike plugin electric vehicles, FCEVs need an entirely new refueling infrastructure network. To date, only 48 hydrogen refueling stations are operational in California. This number will need to increase substantially for FCEVs to become a viable option for consumers. Researchers at the University of California, Davis surveyed more than 700 FCEV drivers about their use of hydrogen fueling stations in California to understand consumer preferences and inform the development of future hydrogen infrastructure.

Related Publications

research report

Investigating Hydrogen Station Use and Station Access in California Using a Survey of Fuel Cell Vehicle Drivers

research report

Investigating Hydrogen Station Use and Station Access in California Using a Survey of Fuel Cell Vehicle Drivers

Publication Date

April 22, 2022

Associated Project(s)

Identifying Gaps in California’s Hydrogen Fueling Station Network through an Assessment of the Refueling Behavior of Fuel Cell Vehicle Drivers

Author(s)

Adam Davis, Gil Tal, Scott Hardman

Areas of Expertise

Zero-Emission Vehicles & Low-Carbon Fuels

View research report

Abstract

California has set a goal of reaching 100% zero-emission vehicle (ZEV) sales by 2035. Most ZEV sales to date have been battery electric vehicles (BEVs) or plug-in hybrid electric vehicles (PHEVs), while fuel cell electric vehicles (FCEVs) make up only a small portion of ZEV sales. The market for FCEVs may be partially constrained because, unlike battery electric vehicles and plug-in hybrid electric vehicles, they cannot use any existing infrastructure. This research investigates FCEV driver’s use of hydrogen stations in California (of which there are 47 in operation) with the goal of informing the development of hydrogen infrastructure. Hydrogen station use was studied using results from a 2017 survey of 395 fuel cell electric vehicle (FCEV) owners and a 2018 survey of 328 FCEV owners. The results show FCEV drivers use on average 2.4 hydrogen stations. The average shortest distance FCEV owners would need to travel from home, work, or their commute to a hydrogen refueling station was 10 miles. Those whose most-used station was not the closest station available were more likely than those whose most-used station was the closest to use renewable hydrogen, suggesting that some drivers may prefer renewable hydrogen. Currently, the percentage of California census block groups with one, two, and three hydrogen stations within 10 miles of households are 52.4%, 25.6%, and 22.5%; these census block groups are concentrated primarily in large metropolitan areas. Finally, 70% of FCEV owners said they would not have purchased the vehicle if their primary station had not been available, pointing to the importance of station availability to FCEV adoption.

Related Publications

policy brief

Refueling Behavior of California Fuel Cell Vehicle Drivers

policy brief

Creating Dark, Quiet Paths for Wildlife Approach to Highway Crossing Structures

Publication Date

April 15, 2022

Associated Project(s)

Improving Light and Soundscapes for Wildlife Use of Highway Crossing Structures

Author(s)

Aaron Bass, Adetayo Oke, David Waetjen, Fraser Shilling, Sean McDowell, Travis Longcore, Winston Vickers

Areas of Expertise

Infrastructure Delivery, Operations, & Resilience

View policy brief

Abstract

Transportation and other agencies and organizations are increasingly planning and building under- and over-crossing structures to allow wildlife to traverse busy highways. Research has shown that traffic noise and light can impede wildlife species from using these structures. However, existing guidance in the field of wildlife crossing design inadequately addresses how structural and vegetation elements can be used to reduce such disturbance. If wildlife is hesitant to or refuses to approach structures due to noise, light, and other factors, then the structures may have a much lower benefit-to-cost ratio than expected. To help address this gap in guidance for design, a research team led by UC Davis used field measurements and modeling of light and noise from traffic to inform and test wildlife crossing designs. The researchers developed wildlife-responsive designs using berms, barriers, and new paths for two crossings being considered by the California Department of Transportation: 1) the proposed Wallis Annenberg wildlife over-crossing (WAOC) across US 101 in the city of Agoura Hills, and 2) a potential over-crossing across Interstate 15, south of the City of Temecula (TOC). The researchers identified key limitations and opportunities for each design approach and concluded that creating “dark and quiet paths” could increase the wildlife-responsiveness of the designs.

Related Publications

research report

Improving Light and Soundscapes for Wildlife Use of Highway Crossing Structures

research report

Guardrails on Priced Lanes: Protecting Equity While Promoting Efficiency

Publication Date

April 20, 2022

Associated Project(s)

Guardrails on Priced Lanes: Protecting Equity While Promoting Efficiency

Author(s)

Bryan Graveline, Gregory Pierce, Michael Manville

Areas of Expertise

Safety, Public Health, & Mobility Justice Transportation Economics, Funding, & Finance

View research report

Abstract

Can congestion pricing be implemented in a way that protects vulnerable residents of California? This report examines that question from two perspectives. First, we empirically estimate the size of the vulnerable population likely to be impacted if congestion pricing were introduced on California’s urban freeways. The research team’s estimates suggest that 13% of households, as a result of their low incomes and current travel habits, might be unduly burdened by a freeway tolling program in California. Second, we consider ways to mitigate these burdens. In particular, we compare freeway use to the use of other metered network infrastructure, like electricity grids or water systems. The research suggests that assistance programs from these utilities provide a useful model for protecting low-income drivers from road prices, and further notes that policymakers would be less constrained in progressively redistributing congestion toll revenue than they would be in redistributing utility revenue.

published journal article

Direct measurements of ozone response to emissions perturbations in California

Publication Date

April 14, 2022

Associated Project(s)

Measuring Changes in Air Quality from Reduced Travel in Response to COVID-19

Areas of Expertise

Safety, Public Health, & Mobility Justice Travel Behavior, Land Use, & the Built Environment

View published journal article

Abstract

A new technique was used to directly measure O3 response to changes in precursor NOx and volatile organic compound (VOC) concentrations in the atmosphere using three identical Teflon smog chambers equipped with UV lights. One chamber served as the baseline measurement for O3 formation, one chamber added NOx, and one chamber added surrogate VOCs (ethylene, m-xylene, n-hexane). Comparing the O3 formation between chambers over a 3-hour UV cycle provides a direct measurement of O3 sensitivity to precursor concentrations. Measurements made with this system at Sacramento, California, between April–December 2020 revealed that the atmospheric chemical regime followed a seasonal cycle. O3 formation was VOC-limited (NOx-rich) during the early spring, transitioned to NOx-limited during the summer due to increased concentrations of ambient VOCs with high O3 formation potential, and then returned to VOC-limited (NOx-rich) during the fall season as the concentrations of ambient VOCs decreased and NOx increased. This seasonal pattern of O3 sensitivity is consistent with the cycle of biogenic emissions in California. The direct chamber O3 sensitivity measurements matched semi-direct measurements of ratios from the TROPOspheric Monitoring Instrument (TROPOMI) aboard the Sentinel-5 Precursor (Sentinel-5P) satellite. Furthermore, the satellite observations showed that the same seasonal cycle in O3 sensitivity occurred over most of the entire state of California, with only the urban cores of the very large cities remaining VOC-limited across all seasons. The O3-nonattainment days (MDA8 O3>70 ppb) have O3 sensitivity in the NOx-limited regime, suggesting that a NOx emissions control strategy would be most effective at reducing these peak O3 concentrations. In contrast, a large portion of the days with MDA8 O3 concentrations below 55 ppb were in the VOC-limited regime, suggesting that an emissions control strategy focusing on NOx reduction would increase O3 concentrations. This challenging situation suggests that emissions control programs that focus on NOx reductions will immediately lower peak O3 concentrations but slightly increase intermediate O3 concentrations until NOx levels fall far enough to re-enter the NOx-limited regime. The spatial pattern of increasing and decreasing O3 concentrations in response to a NOx emissions control strategy should be carefully mapped in order to fully understand the public health implications.

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policy brief

On-Road Motor Vehicles No Longer Dominate Ozone Formation

research report

Measuring Changes in Air Quality from Reduced Travel in Response to COVID-19

research report

Bus Operations of Three San Francisco Bay Area Transit Agencies during the First Year of the COVID-19 Pandemic

Publication Date

April 11, 2022

Associated Project(s)

Bus Operations of Three San Francisco Bay Area Transit Agencies during the First Year of the COVID-19 Pandemic

Author(s)

Alex Kurzhanskiy, Servet Lapardhaja

Areas of Expertise

Public Transit, Shared Mobility, & Active Transportation

View research report

Abstract

From March 2020 through March 2021, researchers monitored three San Francisco Bay Area transit agencies: two large – Alameda-Contra Costa Transit District (AC Transit), Valley Transportation Authority (VTA); and one small – Tri Delta Transit. As the lockdown was imposed in response to the COVID-19 pandemic, white-collar commuters, students, and the elderly stopped using public transit. Initially, ridership fell 90 percent, and then over the year slowly climbed to less than 50 percent for AC Transit and VTA, and to around 60 percent for Tri Delta Transit. The pace of recovery was not steady as ridership declined during protests in June 2020, during fare reinstatements in autumn 2020, and during the second COVID-19 wave in winter 2020-21. Agencies’ responses to the pandemic consisted of three parts: 1) maintaining the health and safety of their employees; 2) minimizing the COVID risk for their riders by keeping buses clean and enabling social distancing through capping the number of passengers on buses; and 3) changing their service. There was a direct relationship between the socioeconomic status of the population and transit ridership during the year studied. Higher ridership was observed in low-income areas with a high percentage of Latino, Black, and Asian populations. These are generally renters, who do not have a car, but have to go to work either because they are essential workers and/ or are undocumented immigrants who cannot afford to stay jobless. On the other hand, in wealthy areas of the Bay Area transit activity all but disappeared.