UC Davis Institute of Transportation Studies

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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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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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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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.

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.

Transportation access is a significant issue in low-income, rural, and otherwise underserved communities in the US, with few affordable and reliable alternatives to car ownership. Carsharing is one promising alternative to improve access among marginalized communities. Grant programs in California have funded pilot electric carshare services. But little is known about the long-term financial sustainability of these services and how their costs and revenues compare those of transit. In this study, a financial model was used to estimate the net operating income (fare revenue minus costs) for Míocar, an electric carsharing service in marginalized suburban and rural communities. The estimated net operating income per month was −$1561, under current operating conditions, and ranged from −$1255 to −$1623 depending on simulated changes to fleet size, pricing, and usage rates. These negative net operating incomes correspond to a shortfall (or need for subsidies) of 68% to 92% of operational costs. Míocar could achieve a higher ratio of fare revenues to operational costs (13%) than existing transit (3 to 8%). To minimize required subsidies, electric carshare operators and prospective carshare communities should carefully consider hub locations (which can affect usage rates), the number of vehicles per hub, and the expected demand over time.

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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Post-collision travel behavior and effects on road safety perception are not well-understood. To quantify the ways thatcrash-related experiences shape the way individuals think about travel, we conducted four focus group discussions with people who had been involved in a crash or near miss or whose relatives or friends experienced one. Several themes emerged from the discussions. Participants changed their travel behavior after experiencing a collision by modifying their travel mode, travel frequency, trip purposes, or vehicle types. Participants developed an enhanced awareness about potentially unsafe behaviors of other road users and road environments and adopted more cautious attitudes toward their own travel. Many participants experienced long-term stress as a result of the incidents, including fear, behavior modification, or travel avoidance. Participants offered several recommendations, including the need for safer infrastructure, improved road user visibility, a shift in media narratives, educational programs, and policy changes focused on land use and transportation synergies.

The aviation sector in California is facing increased pressure to reduce its carbon footprint, leading to a growing interest in alternative fuel aviation (AFA) technologies such as sustainable aviation fuel (SAF), as well as electric- and hydrogen- powered aircraft. The report develops a California Aviation Energy Model (CAVEM), examining various AFA technologies and analyzing possible policy options. The analysis emphasizes the importance of SAF in the short term, with projections indicating sufficient supply for intrastate flights and capped vegetable oil-based fuel consumption. Long-term efforts are focused on electric and hydrogen-powered aircraft, which remain in the early stages of development. Electrification of intrastate flights is deemed feasible, with estimated electricity consumption amounting to a small percentage of overall electricity generation. The report highlights the necessity for additional policy incentives (such as tax exemptions) and a comprehensive policy framework to effectively promote sustainable aviation in the long run.