UC Davis Institute of Transportation Studies

Guidelines for the California Environmental Quality Act require the mitigation of projected increases in vehicle miles traveled (VMT) stemming from highway expansion projects. Quantifying the likely effects of proposed mitigation measures enables an assessment of the degree to which the mitigation program offsets the estimated increase in VMT for a project. The purpose of this report is to provide an overview of possible estimation methods for 45 mitigation strategies and recommendations on the most appropriate method for estimating the reduction in the number of miles of vehicle travel that could be expected to result from the implementation of a specific measure. The methods take into account the extent of the measure but may not account for the specific context. In general, two types of methods are available: travel demand forecasting models, and effect-size approaches. For several measures, this report concludes that the reduction in VMT cannot be estimated based on the available evidence. The Evidence Assessment Report provides as assessment of the strength of the evidence for each of the measures (Handy et al., 2024).

In 2018, pursuant to Senate Bill (SB) 743 (2013), the Governor’s Office of Planning and Research (OPR) and the California Natural Resources Agency promulgated regulations and technical guidance that eliminated automobile level of service (LOS) as a transportation impact metric for land development projects under the California Environmental Quality Act (CEQA), and replaced it with Vehicle Miles Traveled (VMT). The authors investigated the equity effects of VMT mitigation measures and developed a framework for evaluating those effects at the project level. The authors then applied the framework to two highway expansion case studies in California. They found that most VMT mitigation would be implemented at least partially within the project impact areas, as well as some disadvantaged communities, but would generally benefit communities outside of the project area, too. Most of the proposed mitigation measures would not displace existing residences or businesses or pose a significant risk of gentrification. Many of the measures showed substantial potential to improve accessibility to jobs, though less potential to improve accessibility to grocery stores. Community engagement and empowerment was harder to gauge. Overall, the five-part framework can provide a first-cut assessment of the equity effects of VMT mitigation measures during the environmental review phase of VMT-generating projects, like roadway expansions.

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Plug-in electric vehicles (PEVs), including both battery-electric vehicles (BEVs) and plug-in hybrid electric vehicles (PHEVs) are crucial forreducing emissions and meeting sustainability targets, yet their adoption has been limited primarily to higher-income and new car buyers, leaving most low-income households without access. To help inform policies that will accelerate access to used BEVs in particular, this study explored car buying behavior, costs, and usage within and between groups defined by vehicle condition (new vs. used), fuel type(battery-electric vehicles [BEVs] vs. internal combustion engine vehicles [ICEVs], and income level. BEV owning, new-car buying, andhaving higher incomewere each associated with one another. On average the proportion of total income spent on vehicle-relatedexpenses is at least six times higher for householdswith incomes less than $75,000 than householdswith incomes of $250,000 or more. While BEVs offer savings in maintenance and fuel cost compared to ICEVs, the initial price for both new and used BEVs may need to be subsidized to alleviate cost burden for lower-income households. Used car buyers, ICEV owners, and lower-income householdspredominantly do not purchase or maintain their vehicles at automaker dealerships and tend to buy older vehicles withmore mileagethan would be covered by BEV warranties. These findings have implications for the current structure of financial incentives being limited to automaker dealerships. Other possible barriers to BEV uptake for lower-income households and used car buyers, include reliability concerns and limited home charging access. BEV adoption across all income groups could be increased by broadening eligibility for incentives, enhancing battery warranties, offering battery replacement rebates, and expanding home charging infrastructure.

The transportation sector contributes significantly to emissions, with heavy-duty (HD) vehicles responsible for a disproportionately large share. Zero-emission trucks, particularly battery electric trucks (BETs), have emerged as potential solutions to reduce these emissions. BETs offer benefits such as high energy efficiency with low operating noise while facing the challenges such as range anxiety and inadequate infrastructure. This report presents a survey of the latest advancements in battery technologies and primarily focusing on Class 7 and Class 8 heavy-duty vehicles due to their critical role in freight transport. This report further provides information of the status and future expectations of BETs. Finally, a feasibility analysis is presented to assess the battery requirement and operating cost for a 410-mile route from Long Beach, CA to San Francisco, CA. The results highlight the importance of charging scheduling and strategic planning for infrastructure to lower the operating cost and accelerate the widespread adoption of zero-emission trucks. These findings aim to offer insights for policymakers and researchers working toward sustainable freight transport. 

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In this report, the authors propose an online and large-scale rideshare system that can dynamically match passenger requests with drivers and provide efficient routes to the drivers. The authors developed a greedy insertion-based routing procedure to route thousands of requests in an hour. They incorporated flexible meeting point selection into the framework, which can reduce travel distances for both drivers and passengers. The authors implemented an online incentive and cost-sharing system that can incentivize drivers and passengers for their ride time limit violations and share the cost of a rideshare trip among the passengers fairly. The authors incorporated a request prediction and detour mechanism into the ridesharing framework. To get the most updated travel time and study the effects of ridesharing in a road network, theauthors also incorporate a simulation approach into the framework. Numerical experiments performed on the New York Taxicab dataset and a rural dataset based on Kern and Tulare Counties, California, show that the proposed framework is effective, matching thousands of requests per hour. Results also show that ridesharing can cost significantly less compared to ride-hailing services such as Uber or Lyft, and incorporating flexible meeting points can reduce travel distance by 4% on average. Simulation studies show that ridesharing can reduce total vehicle miles traveled by 13% in Manhattan on average. The proposed framework can help transportation officials design real-time and city-scale rideshare systems to alleviate traffic congestion problems in California. 

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Transportation infrastructure construction and maintenance consume energy and finite resources, and have substantial environmental impacts, primarily from the manufacturing of cement, concrete, asphalt, and steel. New feedstock materials and technologies for producing these materials can result in lower life cycle costs, use of local materials, creation of local employment, and reduced environmental impacts. These goals point to the urgent need for adopting innovative alternatives. However, implementation requires confidence on the part of materials producers, contractors, and infrastructure owners that the new materials and technologies can achieve these goals. Implementation demands rigorous testing, risk management, and stakeholder confidence in the engineering performance, environmental benefits, and economic viability of new materials and technologies. This report introduces a structured evaluation framework, “Lab2Slab2Practice,” aimed at accelerating the adoption of these new materials and technologies. Key strategies include leveraging social- behavioral-change models, such as the Unified Theory of Acceptance and Use of Technology and Kotter’s 8-Step Change Model, to mitigate risks and facilitate adoption. A comprehensive review of prior successful government programs and initiatives, including AASHTO’s Superpave and Pavement Mechanistic-Empirical Design tools, underscores the importance of interagency collaboration and support, rapid experimentation, theoretical simulations, and engagement by owners (primarily departments of transportation), contractors, and other stakeholders. Regional centers are proposed as clearinghouses to systematically evaluate materials across Technology Readiness Levels, emphasizing engineering performance, scalability, and constructability. Public-private coalitions are proposed to fund these centers, ensuring transparent dissemination of findings and stakeholder training. With sufficient resources and alignment of federal, state and industry support, the framework targets reducing material adoption timelines from over a decade to 5 years or less, moving materials from ideas to use in standard practices, and improving cost-effectiveness and environmental benefits.

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Public transit ridership has declined in major US cities over the past decade. Integrating traditional fixed-route transit with flexible microtransit has been proposed to enhance ridership, mobility, accessibility, and sustainability. This project surveyed California transit agencies on their microtransit services to identify challenges to integrating them with fixed-route services. An agent-based model combining the two modes of transit was developed to evaluate different operational designs. FleetPy, an open-source simulation tool, modeled microtransit dynamics. The study examined design impacts, such as fixed route headways and microtransit fleet size, in downtown San Diego and Lemon Grove, California. Results showed that while microtransit reduces fixed-route ridership and requires higher subsidies, it significantly boosts job accessibility.

A robust body of empirical research demonstrates that as roadway supply increases, vehicle miles traveled (VMT) generally does, too. The evidence is particularly strong with respect to major roadways, like interstate highways (class 1), other freeways and expressways (class 2), and principal arterials (class 3). However, previous literature reviews have found limited empirical evidence as to the relative magnitude of the induced travel effect of expanding minor arterials, collector streets, and local roads. Previous reviews have similarly not reported empirical research on the induced travel effects of other types of roadway facilities, such as auxiliary lanes, ramps, or other types of interchanges. In this project, the authorsconducted a systematic literature review on the induced travel effects of minor arterials, auxiliary lanes, and interchanges (including simple on/off ramps). The authors found that the empirical literature remains limited with respect to auxiliary lanes and interchanges. They found eight studies that include minor arterials in their empirical estimates of induced travel, which collectively indicate that the induced travel elasticity for class 4 minor arterials could be similar to that of class 1-3 facilities. However, none of the studies isolated the induced travel effect from minor arterials specifically. Going forward, the report suggests avenues for future research to help close these research gaps. For example, the authors recommend using case studies of individual roadway expansions to better understand the induced travel effects specific to ramps, interchanges, minor arterials, and auxiliary lanes within specific contexts, especially where larger studies (across multiple facilities, geographies, etc.) have not yet been done. 

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Median barriers are usually constructed to reduce head-on-crashes between vehicles on undivided highways. Because of their position in the center of the traveled right-of-way, median barriers could affect wildlife movement across the right-of-way, decreasing wildlife connectivity. The authors coordinated and met with staff from several Caltrans Districts to gain understanding of their issues related to median barriers and wildlife permeability. The authors used previously and newly collected wildlife-vehicle collision (WVC) observations to test whether or not median types have different effects on unsuccessful wildlife crossings of the road surface. The authors used Generalized Linear Models (GLM) to compare WVC rates among median treatment types in three Caltrans Districts (2, 4, 9) for four wildlife species. The primary findings were that there are effects of median types on rates of WVC and that these effects varied by species and to some degree by geographic region (represented by Caltrans District). The primary finding is that fewer wildlife enter roadways and are killed in the presence of constructed median types than other types. Although this may result in a reduction in WVC, it also results in a reduction in wildlife permeability as most roadways do not have crossing structures and therefore attempts at wildlife permeability will be across the road surface. 

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The processes in the pavement life cycle can be defined as: material extraction and production; construction; transport of materials and demolition; the use stage, where the pavement interacts with other systems; the materials, construction, and transport associated with maintenance and rehabilitation; and end-of-life. Local governments are increasingly being asked to quantify greenhouse gas emissions from their operations and identify changes to reduce emissions. There are many possible strategies that local governments can choose to reduce their emissions, however, prioritization and selection of which to implement can be difficult if emissions cannot be quantified. Pavement life cycle assessment (LCA) can be used by local governments to achieve the same goals as state government. The web-based software environmental Life Cycle Assessment for Pavements, also known as eLCAP has been developed a project-level LCA tool. The goal of eLCAP is to permit local governments to perform project-level pavement LCA using California specific data, including consideration of their own designs, materials, and traffic. eLCAP allows modeling of materials, transport, construction, maintenance, rehabilitation, and end-of-life recycling for all impacts; and in the use stage it considers the effects of combustion of fuel in vehicles as well as the additional fuel consumed due to pavement-vehicle interaction (global warming potential only). This report documents eLCAP and a project that created an interface for eLCAP that is usable by local governments.