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Open Access Publications from the University of California


The primary mission of the UC Davis Institute of Transportation Studies is research - cross-disciplinary inquiries into emerging transportation issues with great societal significance. It draws upon campus researchers and graduate students from a variety of disciplines, and also upon other universities and research centers around the world.

Institute of Transportation Studies

There are 742 publications in this collection, published between 1991 and 2019.
Policy Briefs (11)

Electrifying Ride-Sharing: Transitioning to a Cleaner Future

Incentives for plug-in electric vehicles (PEVs) are typically designed to encourage broad consumer adoption of the new technology. However, maximizing the emissions benefits from electrifying the transportation sector also requires incentives targeted at stakeholders with high travel intensity, i.e., those with particularly high passenger occupancy and/or vehicle-miles traveled (VMT). This policy brief focuses on one such class of stakeholders: transportation network companies (TNCs) such as Uber and Lyft. It examines empirical data of electric vehicle use in TNCs and discusses research findings on the potential impacts of electrifying TNCs. It also raises important considerations for the development of future policy.

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Traffic Noise and Light May Affect Wildlife Use of Highway Crossing Structures

Roads and highways act as barriers to wildlife. They disrupt movement of wildlife populations and connectivity between communities of interacting species. Transportation organizations and many wildlife agencies see highway crossing structures for wildlife as critical to mitigating highway barrier effects. These structures are optimistically assumed to be effective for most species, most of the time, but are seldom critically investigated.

Wildlife use of highway crossing structures can be highly variable and dependent on structural attributes, human use, and traffic conditions. Studies of animal behavior suggest that wildlife aversion to roadways—and possibly to crossing structures—could be related to traffic noise and light. If transportation organizations and wildlife agencies can confirm this effect they may be able to design more effective wildlife crossing structures and manage existing structures to increase their use by wildlife.

This policy brief discusses findings from research that measured traffic noise levels and used camera traps placed at 20 bridges and culverts in California that were known from previous work to pass at least one species.

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Travel Effects and Associated Greenhouse Gas Emissions of Automated Vehicles

Automated vehicles (AVs) may significantly disrupt our transportation system, with potentially profound environmental effects. This policy brief outlines the mechanisms by which AVs may affect the environment through influencing travel demand, as well as the magnitude of these effects on vehicle miles travelled (VMT) and greenhouse gas (GHG) emissions. Personal AVs and AV taxis (or ride-hailing services) are likely to increase VMT and GHG, exacerbate traffic congestion in city centers, and potentially lead to suburban sprawl. Electrification and vehicle sharing may reduce some of these environmental effects, but targeted policies must be put in place to ensure that these solutions are effective.

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Research Reports (29)

Development of a Freight System Conceptualization and Impact Assessment (Fre‐SCANDIA) Framework

The freight system is a key component of California’s economy, but it is also a critical contributor to a number of externalities. Different public agencies, private sector stakeholders, and academia engaged in the development of the California Sustainable Freight Action Plan (CSFAP). This plan put forward a number of improvement strategies/policies. However, the freight system is so complex and multifaceted, with a great number of stakeholders, and freight operational patterns, that evaluating or assessing the potential impacts of such strategies/policies is a difficult task. To shed some light, this project develops a freight system conceptualization and impact assessment framework of the freight movements in the State. In doing this, the framework assesses the impact of commodity flows from different freight industry sectors along supply chains within, originating at, or with a destination in the state of California.

The conceptual framework analyzes the freight flows in supply chains, and the type of freight activity movements and modes. The framework uses a Life Cycle Assessment (LCA) Methodology. The framework could be extended to support multidimensional cost/benefit appraisals for both direct benefits (e.g., delays, costs, accidents, maintenance) and social benefits to non-users which include impacts on regional and national economies as well as environmental and health impacts. This report discusses the main components of the conceptual framework based on a comprehensive review of existing methodologies. The implementation is limited to the Life Cycle Impact Assessment (LCIA) following the Environmental Protection Agency’s Tool for Reduction and Assessment of Chemicals and Other Environmental Impacts (TRACI).

The report describes the results from the LCIA implementation for a number of case studies. Specifically, the work estimated the impacts of moving a ton of cargo over a mile for various industry categories and commodity types. These results show the relative difference across industries and commodities and could serve to identify freight efficiency improvement measures in the state of California.

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Status Review of Oregon’s Clean Fuels Program, 2016–2018 Q3 (Revised Version)


As part of the state’s overall strategy to reduce greenhouse gas (GHG) emissions, Oregon’s Clean Fuels Program (CFP) aims to reduce transportation sector emissions by incentivizing innovation, technological development, and deployment of low-emission alternative fuels and vehicles. It isdesigned as a performance standard, rather than a prescriptive approach to emissions reduction. It sets an annual declining target in fuel carbon intensity (CI) with a goal of 10% reduction by 2025 relative to 2015 levels.

The CFP has been in effect for three years, with relatively small but growing CI reduction targets of 0.25% in 2016, 0.5% in 2017, and 1.0% in 2018, with a 2019 CI target of 1.5%. The CFP had 163 registered parties and 283 transportation fuel pathways available for use as of the end of 2018.

From 2016 through 2018 Q3, total emissions reduction requirements were 2.4 million metric tons (MMT) CO2e and reported emissions reductions were 2.0 MMT CO2e, representing overcompliance of over 421,000 tons CO2e and creating a systemwide “bank” of program credits(each representing 1 MT CO2e) that can be used to meet future targets. Data for 2018 lacked residential electricity credits at the time of writing.

The program generated excess credits relative to deficits in every quarter through 2017. With 2018 electricity credits not yet reported, 2018 deficits through Q3 exceeded credits by under 1,700, well below the 30,000 credits generated by residential electricity in 2017 Q1–Q3, and theabout 29,000 credits for the same category that would be generated under 2018 standards given the same energy.

Aggregate alternative fuel energy consumption remained approximately stable over the program period—the program’s operation thus far. Ethanol contributed the largest share of alternative fuel and remained between 10% and 11% by volume of blended gasoline, at or just above the“blendwall” of 10% blends, through the period. Between 2016 and 2017, the only two years of complete data, transport energy from fossil natural gas, biogas, propane, and non-residential electricity each grew by over 50%, and from biodiesel grew by over 7%.

The average annual CI rating for most reported alternative fuels declined between 2016 and 2018 through Q3, including the biggest volume contributors, ethanol (just under 1.5% decline) and biodiesel (just over 17% decline).

Prices of CFP compliance credits (each representing 1 MT CO2e) remained in the $40–$50 range through 2016 and 2017. The yearly average increased to $84 in 2018 as volumes traded also rose. Data through March 2019 indicate an average price around $145.

Oregon’s CFP shares some design similarities with California’s Low Carbon Fuel Standard(LCFS), but also has some differences in terms of program targets and baseline fuel blends, treatment of indirect land use change, residential electricity for electric-vehicle (EV) charging, and other credit generation and credit market elements. The programs, along with a similar policyin British Columbia, are part of the Pacific Coast Collaborative commitment to low carbon fuels and economies among these jurisdictions. Washington state is currently considering a similar clean fuel standard as part of its legislative process.

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Framework for Life Cycle Assessment of Complete Streets Projects

A multitude of goals have been stated for complete streets including non-motorized travel safety, reduced costs and environmental burdens, and creation of more livable communities, or in other words, the creation of livable, sustainable and economically vibrant communities. A number of performance measures have been proposed to address these goals. Environmental life cycle assessment (LCA) quantifies the energy, resource use, and emissions to air, water and land for a product or a system using a systems approach. One gap that has been identified in current LCA impact indicators is lack of socio-economic indicators to complement the existing environmental indicators. To address the gaps in performance metrics, this project developed a framework for LCA of complete streets projects, including the development of socio-economic impact indicators that also consider equity. The environmental impacts of complete streets were evaluated using LCA information for a range of complete street typologies. A parametric sensitivity analysis approach was performed to evaluate the impacts of different levels of mode choice and trip change. Another critical question addressed was what are different social goals (economic, health, safety, etc.) that should be considered and how to consider equity in performance metrics for social goals. This project lays the foundation for the creation of guidelines for social and environmental LCAs for complete streets.

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Recent Work (595)

The Transition To Electric Bikes In China: History And Key Reasons For Rapid Growth

Annual electric bike (e-bike) sales in China grew from 40,000 in 1998 to 10 million in 2005. This rapid transition from human-powered bicycles and gasoline-powered scooters to an all-electric vehicle/fuel technology system is special in the evolution of transportation technology and, thus far, unique to China. We examine how and why e-bikes developed so quickly in China with particular focus on the key technical, economic, and political factors involved. This case study provides important insights to policy makers in China and abroad on how timely regulatory policy can change the purchase choice of millions and create a new mode of transportation. These lessons are especially important to China as it embarks on a large-scale transition to personal vehicles, but also to other countries seeking more sustainable forms of transportation.

An Integrated Hydrogen Vision for California

This paper concerns the economic and environmental challenges confronting California and the potential role for clean energy systems and hydrogen as an energy carrier in helping to address these challenges. Hydrogen in particular has recently gained great attention as part of a set of solutions to a variety of energy and environmental problems — and based on this potential the current high level of interest is understandable. In our view, however, full realization of the benefits that hydrogen can offer will not be possible without a clear strategy for producing hydrogen from clean and sustainable sources and in a cost-effective manner. One of hydrogen's greatest benefits — having a wide range of potential feedstocks for its production — also complicates the issue of how hydrogen use may be expanded and necessitates careful forethought as key technology paths unfold. We must remember that the additional cost and complexity of building a hydrogen infrastructure is only justified if significant benefits to society are in fact likely to accrue.

This paper has been written for two primary purposes. First, we argue that the time is ripe for an expanded science and technology initiative in California for clean energy development and greater end-use energy efficiency. This initiative should span transportation systems, electrical power generation, and natural gas and other fuel use, and should place the potential for expanded use of hydrogen within this broader context. Second, we specifically discuss potential concepts and strategies that California might employ as it continues to explore the use of hydrogen in transportation and stationary settings. The authors believe that at this stage the question is not if California should continue with efforts to expand hydrogen use, because these efforts are already underway, but how these efforts should be structured given the level of effort that ultimately emerges through various political and corporate strategy processes. However, we feel that it is critical that these efforts take place in the context of a broader "no regrets" clean energy strategy for California.

Greenhouse Gas Reductions under Low Carbon Fuel Standards?

A low carbon fuel standard (LCFS) seeks to reduce greenhouse gas emissions by capping an industry’s carbon emissions per unit of output. California has launched an LCFS for automotive fuels; others have called for a national LCFS. We show that this policy causes production of high-carbon fuels to decrease but production of low-carbon fuels to increase. The net effect of this may be an increase in carbon emissions. The LCFS may also reduce welfare, and the best LCFS may be no LCFS. We simulate the outcomes of a national LCFS, focusing on gasoline and ethanol as the high- and low-carbon fuels. For a broad range of parameters, we find that the LCFS is unlikely to increase CO2 emissions. However, the surplus losses from the LCFS are quite large ($80 to $760 billion annually for a national LCFS reducing carbon intensities by 10 percent), and the average carbon cost ($307 to $2,272 per ton of CO2 for the same LCFS) can be much larger than damage estimates. We propose an efficient policy that achieves the same emissions reduction at a much lower surplus cost ($16 to $290 billion) and much lower average carbon cost ($60 to $868 per ton of CO2).

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White Papers (16)

Local Government Pavement Research, Development, and Implementation Organization in Several States

This white paper presents the results of a survey administered by the University of California Pavement Research Center (UCPRC) exploring the successes, challenges, funding, and organizational structure of six centers in other states that share a similar mission to support the improvement of city and county pavement practices. Five of the six centers that participated in the survey are statewide centers located in Iowa, Minnesota, North Dakota, Ohio and Texas. The sixth is a regional center located in Washoe County, Nevada, the Regional Transportation Commission. These centers were selected as being the nation’s most advanced based on an extensive internet search and discussions with key pavement professionals across the country.

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California Climate Change Target Setting: A Workshop Report and Recommendations to the State of California Based on the Third California Climate Policy Modeling Dialogue and Workshop

California has a range of existing and proposed targets toward a low carbon future. This paper summarizes an analytical review, focused on modeling approaches and what is known about their feasibility and cost. The findings in this paper are based on the Climate Change Policy Modeling (CCPM) forum, which included modelers, policy makers and stakeholders evaluating targets and pathways to low-carbon futures and identifying required policies to achieve goals. The third forum, CCPM-3, was on May 14th, 2018, at the University of California, Davis and provided critical discussion and a gathering of the key experts in this topic area This report builds on the findings of CCPM and integrates with other literature where possible. It includes a review of the CO2-relevant targets, discussion of studies and modeling efforts to assess meeting such targets, including feasibility and cost. This includes analysis in the transportation and energy sectors, as well as land use and carbon sequestration.

What Affects U.S. Passenger Travel? Current Trends and Future Perspectives

The United States is going through an era of unprecedented transformation. Sociodemographic changes, major innovations in information technology, the reorganization of economic activities, and substantial shifts in the urban form of cities all contribute to changing the way Americans live, work, and travel. During the past ten years, transportation demand in the United States has also gone through significant modifications. The use of private vehicles has gone through a period of apparent stagnation. Starting in the mid-2000s, the average per-capita vehicle miles traveled (VMT) have declined, at least temporarily (until 2013), after a long period of steady growth in the previous decades. In addition, an increased portion of Americans live without a car. While the total amount of trips in the country continues to rise, this has not translated into increased car use, and the use of alternative modes (including public transportation and active means of travel) is increasing, even if it still accounts for a rather low portion of mode share. Passenger travel in the United States at the beginning of the 21st century is increasingly multimodal, and (slightly) less reliant on the use of private cars. Travelers are changing their behaviors in response to new alternatives available to them, changes in the characteristics of the old alternatives, and changes in the way they evaluate and value these characteristics. A complex combination of factors is behind the observed trends. The economic crisis from 2007-2009 certainly contributed to reducing total VMT in the country. However, it is not the main cause of the observed changes in travel behavior, and other factors seem to play an important role. In particular, several studies have demonstrated how the observed reduction in car travel actually predates the economic crisis by at least a few years.

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