National Center for Sustainable Transportation

This report examines the electrification of buses, vocational trucks, and construction machinery, as well as the impact of advancements in battery technology on this transition. The electrification of these vehicles and machinery, alongside rapid progress in battery development, is accelerating. This study provides a comprehensive review of current research on lithium-ion and sodium-ion batteries, evaluating their development status and the challenges to commercialization. A keyobjective of this study is to assess the progress of advanced battery development and its influence on the further commercialization of buses, vocational trucks, and construction machinery. Modeling suggests that within the next 7 to 12 years, batteries with energy densities of 500 Wh/kg and 1000 Wh/L will enable electrified construction vehicles andmachinery to match or surpass the performance of current diesel-powered equipment. Electric buses are already commercially available and expanding globally, while electrified construction trucks and machinery have been successfully demonstrated in real-world projects across the U.S., China, and Europe. These electrified machines offer multiple advantages, including lower carbon dioxide (CO₂) emissions, improved efficiency, quieter operation, and reduced maintenance and energy costs compared to diesel-powered counterparts. Manufacturers are optimistic about marketgrowth, particularly given the support of federal and state incentives aimed at reducing CO₂ emissions. Currently, the cost of electrified construction machinery remains relatively high. However, near-term cost projections are uncertain, as they depend not only on the comparative costs of diesel engines, batteries, and electric motors but also on the rate at which prices for electrical components decline in the near future. 

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Since the 1970s, stakeholders have expressed concerns about the ability of transportation travel demand used by metropolitan planning organizations to represent induced travel from expanded highway capacity. Failure to adequately represent induced travel will underestimate vehicle miles traveled and congestion when comparing scenarios with and without highway capacity expansion. To examine the magnitude of potential biases, the authors use the state-of-the-practice transportation demand model, the Sacramento Council of Governments (SACOG) SACSIM19 model, to examine (1) the model's representation of induced travel, (2) the influence of variation in key inputs on vehicle travel and roadway congestions, and (3) the effect of changes in induced travel-related input variables on the comparisons of scenarios with and without highway expansions.

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The Caltrans 2024 Sustainable Freight Academy was held on November 18-21, 2024. The academy consisted of presentations from goods movement professionals and subject matter experts, including those from both public and private organizations. The final group presentation allowed participants to develop their skills in grant writing by applying lessons learned from the course. Participants were divided into eight groups and took on various roles such as Grant Writer, Project Manager, and Industry Partner in order to develop and present a mock Trade Corridor Enhancement Program (TCEP) proposal topic.

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While the United States has long supported basic needs of residents through social welfare programs, policies supporting affordable transportation for lower income individuals have been much more limited. Federal support for transportation includes subsidies to transit agencies and requirements to offer discounted fares to certain groups such as seniors and riders with disabilities, but income-qualified discounts are not required. This study explores opportunities for improving access to transportation affordable programs by gathering insights from existing income qualified transportation benefits. Researchers compare examples of these programs to design features of existing non-transportation benefits to characterize opportunities for increased coordination and standardization. Finally, as the U.S. has seen an increase in recent years of Universal Basic Mobility (UBM) pilots that provide flexible transportation funds, the study incorporates insights from UBM evaluations to understand how UBM design features may be useful to agencies who are pursuing transportation affordable discounts and subsidies. The results suggest that there is significant potential for income-qualified transportation program enrollment both for agencies that do not currently offer these benefits and for agencies that already offer them, and that inter-organizational coordination among stakeholders may be essential in implementing successful transportation affordable discounts or subsidies. Additionally, the structure of income-qualified transportation benefits may vary depending on agency resources. Finally, with transportation equity as growing priority for California and its transit agencies, program administrators may opt for programs with easy access and enrollment rather than those that create barriers to participation through strenuous application and verification procedures. 

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Extreme heat is the leading cause of weather-related mortality in the United States, and extreme heat events are projected to continue to increase in geographic extent, frequency, and severity in the United States as climate change progresses. Transportation infrastructure is a significant driver of the urban heat island (UHI) effect and exacerbating extreme heat events. Efforts to mitigate UHI impacts often focus on reflecting incoming solar radiation (i.e., increasing surface albedo) and providing shade (e.g., planting street trees). However, advanced and novel materials (ANM) for pavements that reduce heat storage, and green stormwater infrastructure (GSI) that promotes evaporative cooling, can provide additional heat mitigation pathways. Sidewalks facilitate non-motorized transportation, and are relatively low-risk, low-cost, and have simple structural requirements compared to other transportation infrastructure. Hence, sidewalks and adjacent planting strips can offer a logical test bed for new materials and designs. With the thermal comfort, safety, and efficiency of users in mind, environmentally responsible designs can also minimize energy embedded in construction materials and help maintain natural ecosystem processes. Although ANMs hold significant promise for heat mitigation, they have not yet achieved widespread implementation. This project systematically reviewed the growing literature related to theapplication of ANMs and GSI to reduce UHI effects and implemented a survey of urban planners and public works engineers to assess the current and planned use of these strategies and identify barriers to implementation. This report summarizes the emergent themes from the systematic literature review, survey results and policy recommendations for an anticipated reading audience of urban policy makers, planners, and practitioners. 

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Natural gas provides an alternative to petroleum-based fuels as an energy source that is being more widely adopted across multiple sectors in California. The viability of natural gas depends on its total life cycle emissions, specifically of those of methane. This paper addresses the possibility of and reason for fugitive emissions of methane from the transportation sector by surveying and quantifying methane plumes from compressed natural gas (CNG) and liquified natural gas (LNG) storage tanks at vehicle fueling facilities in the greater Los Angeles metropolitan area. This project used methane plume images provided by airborne imaging spectroscopy, collected by NASA’s AVIRIS-NG mission, to identify large methane point sources originating from CNG and LNG infrastructure. The periodic methane plume observations were converted into emission rates to provide an estimate for potential methane emissions from NG storage facilities across California. For the population of facilities that were analyzed, four had natural gas storage tanks with emission rates that are higher than the maximum rate specified by the tank manufacturers. The significant disparity between the expected emission rate and the actual emission rate can be explained by tank malfunction, as the number of observed plume events are far higher than what would be expected for a fully operational tank. If the tank malfunction rates found in the group that was analyzed were applied to the entire population of California CNG and LNG facilities, total emissions may be up to 1300 kg CH4 per hour, suggesting a need for leak monitoring and repair to prevent excessive methane emissions from this sector. 

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California's Zero Emission Vehicle (ZEV) mandate targets all new Light Duty Vehicle (LDV) sales to be ZEVs by 2035. However, the current charging infrastructure is not well-developed in California, primarily serving households with home charging setups and leaving a noticeable gap in public charging facilities. This gap is seen as a significant barrier to Battery Electric Vehicle (BEV) adoption within California. This report explores driver charging behavior and their preference for public DC fast charging (DCFC), drawing on Stated Preference (SP) choice experiment data from a survey of 1,102 Plug-in Electric Vehicle (PEV) owners across California.

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Smaller and rural communities are often automobile dependent, a fact that has raised considerable concerns about the equity and effectiveness of market-based climate strategies including carbon taxes and carbon cap and trade schemes in rural states like Vermont. A lack of research and data describing how people in smaller and rural communities respond to changes in transportation costs is a critical gap to informing the design of market-based greenhouse gas mitigation policies and evaluating their potential outcomes. This report describes several related studies that focus on understanding the opportunities and constraints that people face in changing how they travel in small and rural communities in Vermont and also evaluates the equity implications of gas tax alternatives. The research is informed by data collected by the researcher team from interviews, surveys and unique administrative datasets. Findings show that urban, suburban, and rural households all made significant travel adjustments in response to higher gas prices. Urban households were more likely to substitute their mode of transportation or move, and rural households were more likely to adopt an electric vehicle (EV); however, most people in all community types were able to reduce the amount they travel by making fewer or shorter trips. Greater accessibility and more transit options were noted as barriers to change in all communities studied. Significant concerns about the feasibility of EVs were common and also shared across all communities. Overall, these findings suggest that market-based climate policies could be effective, even in smaller and rural communities. The authors also find that many people misunderstand how the gas tax is collected and what it funds, resulting in widely held beliefs that a mileage base fee alternative would be unfair, particularly to rural households. Using motor vehicle registration and inspection records, the researchers demonstrate that a mileage based user fee would be somewhat less regressive than the current gas tax and also less costly than the gas tax to rural households on average in Vermont. They also find that providing simple, factual, information about the gas tax and alternatives can significantly shift public support for gas tax alternatives in Northern New England. 

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The EVALUATE (Electric Vehicle Assessment and Leveraging of Unified models toward AbatemenT of Emissions) project (Phases I and II) develops a rigorous methodology involving a high-fidelity system of systems model (i.e., vehicle powertrain, EV charging profiles and grid dispatch datasets) for the purpose of forecasting the emissions outputs of a class of vehicles and use cases. Phase I findings explored urban trips by households that operate light duty vehicles (LDVs) for daily personal use. Phase II, presented here, focuses on a series of targeted case studies that extend prior work from LDVs operated by individuals to service-oriented vehicles operated by small and medium businesses. Vehicles used in the present study are representative of public service fleets including the following: pickup trucks, vans, Medium Duty (MD) delivery vehicles, and refuse trucks. In one of the study’s simulations for a MD use case where a specific marginal grid generating resource is identified on an hourly basis as the grid’s means of supplying a particular EV charging event, estimated CO2 emissions could be as much as 42% lower than a conventional gasoline vehicle, or as much as 24% higher than a conventional gasoline vehicle. This large variance is purely a function of when and how quickly the vehicle is recharged, and upstream grid factors. This study reveals key insights: (1) Higher temporal resolution is important to develop more accurate estimates of EV CO2 emissions. Along with this, EV charge management is imperative for all use cases, and has profound implications on infrastructure and emissions; (2) Hybrid Electric Vehicles (HEVs) often performed as well as EVs in contemporary simulations on the basis of emissions benefits, suggesting that consideration of an array of vehicle technologies is important; (3) There is a growing need to focus on higher rate EV charging applications (e.g., DCFC), and related implications on grid demands and energy storage, as proxied by large vehicle batteries; and (4) The trend toward increasing electrification of the transportation sector will continue in conjunction with electrification across other sectors (e.g., buildings, data centers, industry). As such, associated cross-sector planning and study of concomitant emissions must be considered in context of other grid trends. Primary contributions of this effort are the development of new methodologies, integration of sub-system models and independent data sources, and decision support tools that estimate the environmental impacts of vehicle electrification. The study’s methodologies and use cases can enhance understanding and scale-up in additional EV-grid applications, sectors and regions.

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International second-hand vehicle (SHV) exports are a multi-billion-dollar market for the US and an integral process in removing older vehicles from the road and enabling a robust new vehicle market. Mexico is the largest importer of SHVs from the US. As the US rapidly increases electric vehicle (EV) sales to meet decarbonization targets for the transportation sector, EVs will be an increasing large fraction of SHVs. While the benefits of EV adoption are numerous, introducing a radically new technology such as EVs without responsive measures in second-hand market regions may lead to an unintended transfer of economic and environmental burdens, especially if waste EV batteries cannot be managed properly. This research undertook a battery material flow analysis, life cycle assessment of SHVs traded from the US to Mexico, and a qualitive analysis of environmental and transport justice implications of SHV trade. The research finds that SHVs disproportionately contribute to waste battery generation in Mexico, and that second-hand EVs are frequently retired early due to a lack of repairability. In terms of life cycle emissions, SH EVs still contribute to reduced GHG emissions and air pollution relative to internal combustion engine vehicles newly sold in Mexico, but at end-of-life, their batteries are being disposed of in landfills, rather than in recycling facilities. From a justice standpoint, coordination between the US and Mexico and anticipatory policies are needed to ensure that only EVs with sufficient remaining battery life are transferred between the US and Mexico, and that sufficient infrastructure exists to safely dispose of waste EV batteries in Mexico.

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