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Road Ecology Center

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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.

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.




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.




Protecting habitat connectivity for wildlife is a management imperative facing agencies and wildlife organizations across the United States. To maintain connectivity and improve highway safety across transportation routes in western Montana, American Wildlands conducted a rapid wildlife linkage and highway safety assessment. This analysis had two primary objectives: 1) to provide a planning tool to direct American Wildlands’ conservation efforts for protection of habitat connectivity across transportation routes; and 2) to provide data and information useful to agencies and other conservation partners. This assessment used four criteria to identify priority areas: i) road kill concentration areas, ii) important wildlife linkage areas, iii) planned transportation projects, and iv) land ownership as an indicator of the likelihood of conservation success. To complete the analysis, kernel density estimation and percent volume contours were used to identify high concentration areas where there is a dual concern for wildlife and human safety based on elevated numbers of road kill. Additional GIS data sets were used to further prioritize the potential priority areas. This process resulted in improved understanding of the road kill concentration areas in western Montana as well as a planning document which can be used by both public and private sector entities to improve local and regional planning and coordination. Critical to the success of this project was an engaged advisory group and a focus on delivery of the analysis results and products to the agencies and other partners. To ensure that advisory group members, representing their respective organizations, endorse and utilize the analysis results in their planning processes we actively encouraged and incorporated member input into the analysis process and data products. Delivery mechanisms (hard copy reports, GIS data, and web access) were agreed upon by the advisory group and are available with the final report. Continued collaborative efforts between public and private entities will be essential to ensure the appropriate level of conservation dollars and effort to meet protection needs in the identified priority areas. Since the western Montana study can be considered a pilot for a possible statewide initiative, the lessons learned may be used to create an improved product at the statewide level. Additionally, we propose this model be considered for application to other western states in need of a wildlife linkage and highway safety planning tool.




In the 1900‘s, the badger population of the Netherlands was estimated to count 2500 to 3000 setts with over 4000 individuals. Between then and the 1960‘s, the number declined drastically and stayed low until the mid-1980‘s with about 400 setts in the whole of the Netherlands. In the 1980‘s a high percentage of the population, locally up to 25%, was killed yearly by road traffic. For this reason the Dutch government implemented mitigation measures such as fauna tunnels and fences. It was easy to monitor the use of such measures. By census we know that the population increased to around 5000 individuals in 2006. But were these “badger tunnels” effective: did the number of traffic victims at these tunnels decrease?

To answer this question we analyzed data on badger traffic victims gathered by NGO Das & Boom and the Center for Transport and Navigation (Rijkswaterstaat) between 1990 and 2006. First, we determined the distribution of victims over motorways, provincial roads and local roads. In absolute terms, most victims were reported from local roads. However, relative to the length of road in the range of the badger, most victims occur at provincial roads.

Second, we tested whether taking mitigating measures resulted in a decrease of traffic victims. Realization of fauna tunnels resulted in a small but significant decrease in the local number of victims, but effects varied from site to site: at most sites, the number of victims was lower, but at some the number of victims was higher after implementation of the measure. Analysis on a local scale should provide a clearer picture of the effect of mitigation measures on badger mortality. Such a study was done in the area ‘Eindegooi’ where the increase of the population of badgers is spectacular. It appears that the increase is related to a package of measures taken in that area.

The challenge for conservation now lies in minimizing victim numbers at local roads. As badger victims occur over a huge length of local roads, mitigation will be difficult. Still, a number of measures are feasible, for example locally designed tunnels and fences, decreasing speed limits or closing roads for through traffic, especially at ‘black spots’ with high numbers of victims.

Cover page of An Analysis of the Efficacy and Comparative Costs of Using Flow Devices to Resolve Conflicts with North American Beavers Along Roadways in the Coastal Plain of Virginia

An Analysis of the Efficacy and Comparative Costs of Using Flow Devices to Resolve Conflicts with North American Beavers Along Roadways in the Coastal Plain of Virginia


Road damage caused by beavers is a costly problem for transportation departments in the U.S. Population control and dam destruction are the most widely used methods to reduce road damage caused by beavers, but the benefits of such measures in some situations are often very short-term. At chronic damage sites, it may be more effective and cost-beneficial to use flow devices to protect road structures and critical areas adjacent to roads. To determine the potential benefits of using flow devices at chronic beaver damage sites, from June 2004 to March 2006 we installed 40 flow devices at 21 sites identified by transportation department personnel as chronic damage sites in Virginia’s Coastal Plain. Following installations, study sites were monitored to determine flow device performance and any required maintenance and repairs. Between March 2006 and August 2007, transportation department personnel were surveyed to collect data on flow device efficacy and comparative costs. As of August 2007, transportation department personnel indicated that 39 of the 40 flow devices installed were functioning properly and meeting management objectives. The costs to install and maintain flow devices were significantly lower than preventative road maintenance, damage repairs, and/or population control costs at these sites prior to flow device installations. Prior to flow device installations, the transportation department saved $0.39 for every $1.00 spent per year on preventative maintenance, road repairs, and beaver population control. Following flow device installations, the transportation department saved $8.37 for every $1.00 spent to install, monitor, and maintain flow devices. Given the demonstrated low costs to build and maintain flow devices, transportation agencies may substantially reduce road maintenance costs by installing and maintaining flow devices at chronic beaver damage sites.




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.