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Open Access Publications from the University of California

Recent Work

The Road Ecology Center at the University of California, Davis integrates ecological sciences, engineering, and social sciences to study the interactions between roads and the surrounding natural and human environment, and to develop sustainable transportation solutions that are environmentally and socially friendly. The purpose of the UC Davis Road Ecology Center is to foster and develop a science of road ecology; to support university-based training and education in road ecology; develop scientifically-sound assessment tools, frameworks, and practices to be used in planning and management of sustainable transportation systems; and to share research findings and information in partnership with environmental scientists, professional organizations, governmental agencies, and public interest groups. As road use continues to increase, there is an urgent need to bring together the research findings of planners, policymakers, educators and researchers in a single archive. Awareness of the pervasiveness of road effects has grown, so that we now have an opportunity to provide information that will help us develop scientific tools to understand the underlying relationships, and to incorporate this understanding in planning today's transportation systems.

Cover page of Adaptive Planning for Transportation Corridors Threatened by Sea Level Rise

Adaptive Planning for Transportation Corridors Threatened by Sea Level Rise


This paper describes a generalizable planning and assessment process for

transportation planning adaptive to sea level rise (SLR). State Route 37

(SR-37) is the California highway most vulnerable to temporary flooding

and permanent inundation as a result of SLR. Like many other coastal highways

in the United States, SR-37 is adjacent to protected coastal systems

(e.g., beaches, tidal wetlands), meaning that any activity on the highway is

subject to regulatory oversight. Both SR-37 and the surrounding marshes

are vulnerable to the effects of SLR. Because of a combination of congestion

and threats from SLR, planning for a new highway adaptive and resilient

to SLR impacts was conducted in the context of stakeholder participation

and Eco-Logical, a planning process developed by FHWA to better integrate

transportation and environmental planning. To understand which

stretches of SR-37 might be most vulnerable to SLR and to what degree, a

model of potential inundation was developed with a recent, high-resolution

elevation assessment conducted using lidar. This model projects potential

inundation by comparing future daily and extreme tide levels with surrounding

ground elevations. The vulnerability of each segment was scored

according to its exposure to SLR effects, sensitivity to SLR, and adaptive

capacity (ability of other roadways to absorb traffic). The risk to each segment

from SLR was determined by estimating and aggregating impacts to

costs of improvement, recovery time (from impacts), public safety impacts,

economic impacts, impacts on transit routes, proximity to communities

of concern, and impacts on recreational activities.

Cover page of Wildlife-vehicle collision hotspots at US highway extents: scale and data source effects

Wildlife-vehicle collision hotspots at US highway extents: scale and data source effects


Highways provide commuter traffic and goods movement among regions and cities through wild, protected areas. Wildlife-vehicle collisions (WVC) can occur frequently when wildlife are present, impacting drivers and animals. Because collisions are often avoidable with constructed mitigation and reduced speeds, transportation agencies often want to know where they can act most effectively and what kinds of mitigation are cost-effective. For this study, WVC occurrences were obtained from two sources: 1) highway agencies that monitor carcass retrieval and disposal by agency maintenance staff and 2) opportunistic observations of carcasses by participants in two statewide systems, the California Roadkill Observation System (CROS; and the Maine Audubon Wildlife Road Watch (MAWRW; Between September, 2009 and December 31, 2014, >33,700 independent observations of >450 vertebrate species had been recorded in these online, form-based informatics systems by >1,300 observers. We asked whether or not WVC observations collected by these extensive, volunteer-science networks could be used to inform transportation-mitigation planning. Cluster analyses of volunteer-observed WVC were performed using spatial autocorrelation tests for parts or all of 34 state highways and interstates. Statistically-significant WVC hotspots were modeled using the Getis- Ord Gi* statistic. High density locations of WVC, that were not necessarily hotspots, were also visualized. Statistically-significant hotspots were identified along ~7,900 km of highways. These hotspots are shown to vary in position from year to year. For highways with frequent deer-vehicle collisions, annual costs from

collisions ranged from US$0 to >US$30,000/km. Carcass clusters from volunteer data had very little or no overlap with similar findings from agency-collected WVC data, during a different time-range. We show that both state agency-collected and volunteer-collection of WVC observations could be useful in prioritizing mitigation action at US state-scales by state transportation agencies to protect biodiversity and driver safety. Because of the spatial extent and taxonomic accuracy at which volunteer observations can be collected, these may be the most important source of data for transportation agencies to protect drivers and wildlife.

Cover page of Wildlife/roadkill observation and reporting systems

Wildlife/roadkill observation and reporting systems


Wherever wildlife habitat and roadways overlap, roadkill seems inevitable. Observing and recording carcasses

resulting from wildlife–vehicle collisions (WVC) provides data critical for sustainable transportation

planning and species distribution mapping. Across the world, systems have been created to record WVC

observations by researchers, highway maintenance workers, law officers, wildlife agency staff, insurers and

volunteers. These wildlife/roadkill observation systems (WROS) can include mobile recording devices for

data collection, a website for data management and visualisation and social media to reinforce reporting


62.1 The specific purpose and goals of the WROS may vary among systems but should always be clearly


62.2 Extensive social networks are needed for comprehensive observation systems.

62.3 Adopt a methodical approach to developing a wildlife/roadkill observation system.

62.4 Analysis and visualisation of data collected within a WROS should correspond to the goals of the


62.5 Address issues in reporter bias by using standardised data collection methods or post hoc analyses.

62.6 The advantages and disadvantages of opportunistic and targeted data collection must be carefully

considered when developing a WROS.

Volunteer science and web‐based information tools have advanced to the point where transportation or

wildlife agencies and their allies can develop, support or implement WROS to improve the sustainability of

transportation systems. However, while numerous WROS have been developed and implemented around the

world, the full potential of many systems has not been realised because they were not developed or maintained

according to the basic principles outlined in this chapter. We provide suggestions and guidance useful

for updating existing systems and developing new ones.

Cover page of Valuation and Crediting Approaches for Transportation and Metropolitan Planning Agencies

Valuation and Crediting Approaches for Transportation and Metropolitan Planning Agencies


Ecosystem services measurement and crediting tools are recognized as important to the transportation planning and project implementation process because they can aid the process of mitigating environmental impacts by reducing transaction costs, improving environmental outcomes, and shortening the time needed to implement projects. Because of this, they have been identified as a key step in the Eco-Logical framework integrating transportation and conservation planning, characterized by a SHRP2 Capacity Program Study as the Integrated Ecological Framework (IEF). Currently, there is not a straightforward methodology for creating a transportation-centric crediting program available throughout much of the US. However, successful programs in California, North Carolina, Oregon, and Washington have all developed approaches cooperatively with the regulatory agencies, state and non-governmental conservation programs, those actively involved in mitigation banking, and agencies or organizations funding restoration activities. An overview of crediting systems and valuation methods and their use at various scales in transportation planning are presented. Current projects and programs are evaluated to identify opportunities and obstacles transportation organizations may encounter when attempting to implement a crediting program.




Stormwater conveyance practices are grounded in industrial design that neglects integration with system processes, economics, and aesthetics. As a result, the greater volume of runoff from impervious surfaces, coupled with smooth and hardened conveyance systems (e.g., pipes and trapezoidal concrete channels), magnifies and transfers energies to the discharge or outfall. Conventional stormwater outfalls cause erosion, conveyance structures fail, stream channels are degraded, in-stream sedimentation increases the influence of localized erosion upstream and downstream of the outfall, and an increasing spiral of degradation results. Local governments are forced to spend scare public funds on remediation measures. Alternatively, the technique of using stream restoration techniques to create a dependable open channel conveyance with pools and riffle-weir grade controls is a regenerative design since the use of these elements result in a system of physical features, chemical processes, and biological mechanisms that can have dramatic positive feedback effects on the ecology of a drainage area. This approach results in the delivery of low energy storm water discharge, potential volume loss through infiltration and seepage, increased temporary water storage, restoration of lowered groundwater, increases in vernal pool wetland area, improved water quality treatment, improvements in local micro-habitat diversity, and provides a significant aesthetic value. These projects are generally a win-win-win arrangement, as conventional construction practices and materials are more expensive, conventional conveyance provides no environmental benefits and are more difficult to permit, and people generally enjoy the aesthetics associated with a well vegetated channel form when compared to the conventional conveyance alternative.

Cover page of Integrating Conservation and Long-Range Transportation Planning Using a Strategic Assessment Framework

Integrating Conservation and Long-Range Transportation Planning Using a Strategic Assessment Framework


The Pikes Peak Area Council of Governments Moving Forward metropolitan transportation planning process introduced a Strategic assessment planning framework to the Pikes Peak region. This framework was selected because it integrates multi-disciplinary qualitative and quantitative information from technical experts and regional stakeholders to determine and weight objectives and indicators within the evaluation process. In order to implement this framework the regional modeling system was updated and several new technical tools added; including Natureserve‟s Vista forhabitat conservation, and Placeways‟ CommunityViz for community impact evaluation. PPACG received funding from the FHWA to investigate integration and initial application of these planning tools at the regional level.

Both the biological impacts of potential transportation investments and potential locations of regional mitigation sites were determined by integrating conservation planning concepts, planned land uses, and transportation planning concepts using Vista software. A matrix was created to describe the compatibility of each conservation species (selected to represent a larger conservation objective) with each land use class. The analyses found that, given current urban development, there should already be serious concerns about the long-term viability of some species and that some rare and imperiled species face significant threats from planned developments. The initial output was reviewed and refined by Colorado Natural Heritage Program ecologists in order to map ecologically relevant areas of conservation importance. This information was then incorporated in the CommunityViz growth scenarios. Several future socioeconomic scenarios and their respective conditions were developed.

The analyses in CommunityViz showed two key factors in the growth and development pattern of the study area. First, it showed that increasing density to support an increased transit system can concentrate growth around transportation corridors meeting or approaching transportation, social and economic goals from public input within the timeframe of the long-range plan. It also showed that a conservation plan could be applied in conjunction with this transit-oriented development to achieve publicly stated conservation goals. Combining transportation and conservation planning could successfully focus development around city centers while relieving development pressure on land that is necessary to meet conservation goals.

The best scoring alternative was not adopted by the elected leaders in the region due to its dependence on changed land uses. The reason for this is that land uses are outside the purview of MPO. However, several smaller projects resulted from the enhanced communication, including the CDOT and the Colorado Springs Stormwater Enterprise each moving water quality mitigation project locations to co-locate with a developer‟s project. This mitigation effort will create more total ecological benefit and an additional cultural amenity.

The primary outcome of the PPACG process is that both citizens and decision-makers are better informed regarding the tradeoffs between transportation investment decisions and other planning and development decisions that were previously made in isolation.

Cover page of Potential Impacts of Climate Change on Urban Flooding: Implications for Transportation Infrastructure and Travel Disruption

Potential Impacts of Climate Change on Urban Flooding: Implications for Transportation Infrastructure and Travel Disruption


Climate change in the Pacific Northwest of America is likely to bring more frequent, heavier winter precipitation as temperature rises. These changes in precipitation patterns have significant implications in hydrology and socioeconomic sectors that could be affected by changes in hydrology. Transportation infrastructure and travel patterns are also vulnerable to potential changes in runoff regimes and stream geomorphology. The 2006 and 2007 winter storms resulted in massive flooding, causing several major road failures in Oregon. While the probability of these extreme events is projected to rise under the global warming scenarios, there is no study investigating this issue in Oregon.

The objectives of the project are threefold. First, we investigate the changes in the frequency and magnitude of winter runoff under climate change scenarios. Second, we determine the probability of road closure for representative road bridges under climate change scenarios. Third, we quantify these changes on transportation chokepoints related to flooding.

We examined two representative urban streams in the Portland Metro area. Johnson Creek and Fanno Creek were chosen because both creeks have historical flow data and exhibit high flooding potential; each also has high road density with high traffic volume. The hydrological processes of the two watersheds, however, are different (Fanno – highly urbanized and steep slope; Johnson Creek – mixed land use with gentle slope); thus, each serves as a good model for other urban watersheds in Oregon. We used the following methodology to conduct our analysis. 1) Hydro-climate modeling: We applied statistically downscaled climate change scenarios for our study sites to predict the anticipated changes in winter precipitation amount and intensity. The US Geological Survey PRMS hydrologic model, together with a statistical model, were used to estimate runoff changes and resultant changes in flood frequency. 2) Stream geomorphology survey and hydraulic analysis: We surveyed channel profiles, patterns, and dimensions at the multiple cross sections of our study sites. The surveyed data were used to calibrate US Army Corp of Engineers‘ HAC-RAS for hydraulic analysis to project future water levels and identify vulnerable bridges and roads under different discharge scenarios. 3) Traffic analysis: We used Metro‘s travel forecast model to determine the potential impacts of road failure and congestion resulting from flooding. The model served as a reasonable and accurate assessment of the outcomes due to traffic disruption.

Our results show that there is a nonlinear relation between precipitation change and urban flooding and that impacts on travel disruption are subject to local hydroclimate and watershed land use conditions. This study is one of few interdisciplinary attempts to assess potential impacts of climate change on the transportation sector. Such integrated knowledge and spatially-explicit modeling is essential for establishing proactive flood and transportation management planning and policies under increasing climate uncertainty.




Centralized planning framework, accelerating habitat fragmentation and growing awareness to animal-transportation issues in Israel have lead to increased demand for ecological considerations during road construction and maintenance. Several governmental bodies have upgraded their requests regarding fauna passages and monitoring, with substantial budget implications. Planning and management decisions on local and regional scale need to consider changes and adaptations required with time. Current project-oriented planning and budgeting make it difficult to maintain a regional, long-term view. Most existing fauna passages were not specifically designed for animals. Guidelines for animal passages are derived from European countries, which differ from Israel in climatic-ecological aspects and in some human activity patterns. Adapting these guidelines to local conditions in order to rationalize and optimize planning, expenditure and results requires more accurate reevaluation of animal needs, testing alternative solutions on small scale before turning to large-scale expensive modifications, and responding to temporal changes.

Cover page of Traffic Volume as a Primary Road Characteristic Impacting Wildlife: A Tool for Land Use and Transportation Planning

Traffic Volume as a Primary Road Characteristic Impacting Wildlife: A Tool for Land Use and Transportation Planning


Based on an analysis of current literature, we developed a Traffic Volume Wildlife Tool that identifies different levels of traffic volume as a means to assess risk to various wildlife species groups, including amphibians, reptiles, birds, and mammals. Each level includes an assessment of when impacts to different species groups begin and when they become a serious threat. Traffic volume, or the amount of traffic using a road, poses substantial negative consequences for many wildlife species, especially as traffic levels increase. Road location and traffic volume are the two most important factors to assess when evaluating a road‘s potential impacts. Increases in traffic volume alter species composition, impedes animal movement, causes direct mortality, and fragments habitat. Based on the existing studies that quantify traffic volume and measure impacts to wildlife, we developed guidelines for use in planning. We discuss how changes in traffic volume affect habitat quality and animal behavior, and which types of species are most vulnerable. We recommend using these data and guidelines in land use and transportation planning and permitting.




The development of infrastructure facilities can negatively impact critical habitat and essential ecosystems. There are a variety of techniques available to avoid, minimize, and mitigate negative impacts of existing infrastructure as well as future infrastructure development. However, such techniques may not always provide the greatest environmental benefit or may do very little to promote ecosystem sustainability. Concern for ecosystem protection, along with legislation and policy initiatives aimed at fostering an ecosystem-based approach, led an Interagency Steering Team to collaborate over a three-year period to write Eco-Logical: An Ecosystem Approach to Developing Infrastructure Projects. The Steering Team shared a vision of an enhanced and sustainable natural environment combined with the view that necessary infrastructure can be developed in ways that are more sensitive to terrestrial and aquatic habitats. Eco-Logical encourages all partners involved in infrastructure planning, design, review, and construction to use existing flexibility in regulatory processes. The Eco-Logical publication puts forth a conceptual framework for integrating plans across agency boundaries and endorses ecosystem-based mitigation – an innovative method of mitigating infrastructure impacts in today’s changing environment. To test the concepts presented in Eco-Logical, the Federal Highway Administration‟s (FHWA) Office of Planning, Environment, and Realty initiated a grant program in 2007. Of the 40 applications from across the country, FHWA funded 14 cooperative agreements and 1 interagency agreement, totaling approximately $1.4 million. The number and diversity of applications indicate a changing climate in the field of transportation with a shift to more ecologically sensitive planning.

The selected grant projects incorporate tools and techniques ranging from the integration of environmental considerations in the transportation planning process to the use of Geographic Information Systems (GIS) and public involvement to integrate infrastructure and conservation plans. For example, one project tests and demonstrates how interagency partnerships and a willingness to adapt existing processes can enhance cultural and environmental stewardship in the long-range transportation planning process. The grant recipients represent state and local departments of transportation, federal and state resource agencies, Metropolitan Planning Organizations (MPOs), local governments, Non-Governmental Organizations (NGOs), and one university. Initial findings from the grant program indicate a successful integration of ecologically sensitive principles into infrastructure planning and project development. By creating and using data-driven tools and processes, the Eco- Logical grant projects show that partnering with resource agencies and stakeholders early in the planning and project development processes enhances the preservation of high-functioning ecosystems.