Develop An Integrated Approach for Assessing Impacts and Mitigation Options to Address Preserving Wildlife

Focus Area

Wildlife & Ecosystems


Natural Resources






Over 3 years

Research Idea Scope

Highways create a multitude of impacts on wildlife movement across the landscape. Some of the
highway impacts result from the structure of the roadway, location of the roadway, traffic
volume, right-of-way (ROW) fencing, concrete dividers, and guardrails. Each of these has the
potential to limit the permeability of the highway to wildlife as they attempt to move across the
landscape. The structural barriers associated with highways include ROW fencing, concrete
dividers, guardrails, noise barriers, retaining walls, and cutslopes. The impacts of these barriers
vary depending on height, placement, and visual permeability. These impacts vary by species
groups. For example, ROW fencing and many types of guardrails may have little impact on the
movements of rodents and other small mammals and amphibians, but may pose serious
restrictions of the movement of large mammals. Conversely, concrete barriers potentially block
rodents, amphibians, and small mammals. Larger and higher concrete barriers may also pose
serious restrictions to larger mammals, particularly those that cannot see over these barriers, or
for animals unwilling to jump over them. Thus, barriers associated with highways pose potential
impacts to a broad range of wildlife species. In combination, these barriers may pose significant
threats to wildlife movements particularly when they occur in combinations along highways in
important wildlife habitats.

There is a need to better understand how various species respond to highway barriers in an integrated approach, which involves simultaneously measuring the impacts of ROW fencing, guardrails, and concrete barriers on multiple species groups.The proposed research would document the impacts of multiple barriers, including ROW fencing, guardrails, noise barriers, retaining walls, cutslopes, and concrete barriers on wildlife in a representative section(s) of Interstate highway in habitats where multiple species of interest are present.

A minimum of two study sites would provide repeatability. Species present in study areas should include amphibians, small mammals, medium-size carnivores, ungulates, and large
carnivores. The objective of the work is to document the permeability of the various barrier
types on the movements of each species group, taking into account existing road design.
Specific information would be collected for each barrier type on the movements of each species
group within the study areas. The cumulative impacts of the multiple barriers on movement
across the highway for each species group would also be documented to produce an
understanding that the highway is or is not permeable to each species group. The reason for the
lack of permeability would be documented as to the type of the problem barrier. To understand if
animals are using existing structures such as underpasses to cross the highway instead of
negotiating the barriers along the highway, it will be necessary to document the use of these
structures within the study area for the same species being monitored in relation to the barriers.
The product of the research will be a synthesis of the impacts of ROW fencing, guardrails, and
concrete barriers on a wide range of species groups in representative areas of Interstate
highways. By understanding the impacts on species groups, it will be possible to highlight the
mitigation possibilities related to each species group for each barrier type. Some of the results
may lead to further research to assess specific mitigation possibilities for certain barrier types in
a repeatable approach. This synthesis will be of national value in determining impacts of such
highway-associated barriers in environmental analyses and in the development of highway
design standards. These data will also be useful in understanding the impacts of highways and
associated barriers on the health of various wildlife populations and on wildlife linkage across
the country at a landscape scale. An additional goal of this work is to make recommendations
for amendments to the AASHTO Green Book on barrier application in ecologically important

TERI Administrator Note (June 2007): Research Completed (See Below)

NCHRP – Evaluation of the Use and Effectiveness of Wildlife Crossings, NCHRP Report 25-27 (2007)

Every year, the costs of personal injuries and property damage resulting from animal/vehicle collisions are considerable. Various means have been employed to mitigate these collisions, with varying degrees of success. In recent years, highway agencies have placed a growing emphasis on protecting the environment. While many smaller species of animals do not pose a threat to vehicles through collisions, they experience significant habitat loss and fragmentation as a result of roadway alignments. Transportation corridors limit the natural movement of wildlife, affecting individual species and ecosystems. There has been considerable research on the provision of wildlife crossings, but there is a lack of data on their effectiveness and on the methods most effective for a particular species in a particular landscape. It also appears that crossings may work well for one species but not for others. A recent international scan on wildlife habitat connectivity documented various strategies and designs used in Europe to improve the connectivity of wildlife habitats. Developing successful designs, methods, and strategies to make roadways more permeable to wildlife is but one aspect of managing highways to avoid or minimize affects to the natural environment and maintaining safety for motorists. There is a need to provide state DOTs with guidance on the use and effectiveness of wildlife crossings to mitigate habitat fragmentation and reduce the number of animal/vehicle collisions on our roadways. The objective of this project is to develop guidelines for the selection (type), configuration, location, monitoring, evaluation, and maintenance of wildlife crossings.

Montana DOT – Wildlife-Highway Crossing Mitigation Measures & Associated Costs/Benefits: A Toolbox for Montana Department of Transportation (2007)

The objective of this project is to aid the Montana Department of Transportation (MDT) with the decision-making process regarding the choice of mitigation structures that reduce animal-vehicle collisions, and provide habitat connectivity for wildlife, for current and future projects. Reducing animal-vehicle collisions and improving habitat connectivity for wildlife across roadways are important factors to consider in highway construction or improvement projects for human safety, economic and ecologic reasons. The estimated 725,000 to 1,500,000 collisions between motor vehicles and wildlife result in more than 200 human fatalities, 29,000 human injuries and over 1 billion dollars in property damage in the United States alone each year. In addition, highways can be a movement barrier to many species, causing habitat fragmentation and, sometimes, reduced survival probability for the population concerned. Engineers and biologists have tested a variety of potential solutions to the safety, economic and ecologic conflicts between wildlife and highways. Many years of work have resulted in substantial knowledge about the application and effectiveness of a wide array of mitigation measures deployed worldwide. However, knowing which mitigation measures address a particular problem, and which would be suitable given local circumstances can be challenging. MDT has contracted with the Western Transportation Institute (WTI) to provide an overview of mitigation measures that reduce animal-vehicle collisions and allow animals to cross the road safely.

FHWA Report FHWA-PL-02-011Wildlife Habitat Connectivity Across European Highways 2002

Habitat and wildlife resources around the world have diminished to the point that transportation agencies are being asked to address impacts to these resources when implementing improvements to transportation systems. The Federal Highway Administration (FHWA), American Association of State Highway and Transportation Officials (AASHTO), and the National Cooperative Highway Research Program (NCHRP) sponsored an international technology scan to learn what actions are being taken in Europe to address habitat and wildlife issues. A delegation of federal, State, and conservation group representatives visited Slovenia, Switzerland,
Germany, France, and the Netherlands to observe and document efforts in Europe.

As a result of the trip, the team formed conclusions and recommendations for U.S. applications in the areas of policy, communications, guidance manuals, and research. In particular, the group recommends (1) including wildlife/transportation issues in the FHWA and AASHTO strategic plans; (2) creating a central source of contact for international exchange of information; (3) developing a number of guidance manuals pertaining to assessment methodologies, interagency coordination, terminology, and structures design; and (4) using pooled funds to study connectivity needs for all types of wildlife; and (5) funding a national connectivity study.

Suggested By

Transportation Research Board 2002 Environmental Research Needs Conference Notes

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