National Center for Sustainable Transportation

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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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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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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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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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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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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