Evaluation of Existing Wildlife Crossing Systems

Focus Area

Wildlife & Ecosystems


Natural Resources







Research Idea Scope

Research should evaluate existing wildlife crossing systems to determine their effectiveness.
Various system types should be compared with respect to wildlife. In evaluating system
effectiveness, consideration needs to be given to whether the design properties of the structure or
the structure location are related to the utilization of the structure. The result of this comparison
should be correlated to wildlife populations and movement patterns. The cost of each type of
system should be compared based on reduction in wildlife mortality, the number of wildlife
species that are served, and the reduction in loss of personal property and human lives.
Determining animal behavior and response to the crossing system, using such technology as
infrared video, is a necessary component of this research. A product of this research needs to
include suggested design criteria for effective wildlife crossing systems for selected wildlife
species of concern.

TERI Administrator Note (June 2007): Research Completed

Montana State University, Bozeman; Guidelines for Designing and Evaluating North American Wildlife Crossing Systems (2005)

The objective of this research project is to provide transportation professionals with the best available information and current technologies on wildlife crossing systems for transportation projects. Effective wildlife fencing and crossing structures can significantly reduce many harmful impacts of roads on wildlife populations. Yet currently there is limited knowledge of how to incorporate these structures for most wildlife species into transportation projects. For example, studies have shown that wildlife use crossing structures, but level of use varies between species of wildlife, locations and landscapes, and the reasons why are unclear. Recommended minimum dimensions have been suggested for some ungulate species, but the needs of wide-ranging species are vague at best. Human activity can significantly influence how wildlife use structures. Others have inferred that crossing structure location, particularly in relation to habitat quality, might be the most important design feature of successful wildlife crossing structure applications. In spite of these valuable kernels of information, gaping holes in our knowledge of functional wildlife passage systems remain. Practically all of the performance evaluations to date have focused on single-species and limited attention has been paid to multiple-species relationships. After nearly a decade of increased activity building crossing structures, engineers and land managers still lack guiding principles as a large void exists in devising functional designs based on criteria that are relevant to real management decisions. It is timely to conduct a critical assessment of the current status of these mitigation measures and experience in an adaptive management process. A growing body of literature and information base has resulted from nearly a decade or more of increased implementation of wildlife crossing systems in North America. This project serves as the first attempt to gather, review and critically analyze current information on ecological criteria and design attributes of wildlife crossing structure planning and performance. We will obtain data on specific passage use from reports in journals, conference proceedings, in-house technical reports and informal contacts with colleagues.

Two connected phases of research are proposed: the first addressing where wildlife crossings
should be located at a fine scale based on wildlife behavior and movement patterns, terrain,
habitat characteristics, and characteristics of the transportation corridor; and the second what
types of structures are most effective for representative wildlife.

The following should be considered when addressing where wildlife crossings should be
located for representative wildlife species:

  • Address how movement patterns of representative species react to highways, wildlife crossings, and related infrastructures, and how topography, habitat character, and the transportation corridors affect wildlife reactions. Many aspects need clarification, including the effects of traffic noise, traffic volume, and traffic speed on wildlife behavior.
  • Assess how terrain and habitat features enhance or detract from the use of wildlife crossings and associated linkage areas. What are the most effective terrain and habitat characteristics to identify when placing crossings and linkage zones for representative species and multiple species?

The following studies should be conducted to determine what types of structures are most
effective for representative wildlife species:

  • What types of wildlife crossing structures are best for representative species such as deer, elk, small mammals, reptiles, and amphibians?
  • What are the best structures for multiple species?
  • How effective are existing structures in promoting wildlife crossings?
  • What are the most cost-effective designs?
  • How can existing crossings such as bridges and culverts be modified to facilitate wildlife movement?
  • What are design elements that generally enhance wildlife use of structures such as fencing, natural light, and opening size?

TERI Administrator’s Note – Related Research

A featured article in the March-April 2007 issue of TR News http://www.trb.org/news/blurb_detail.asp?id=7668) explores Banff  National Park in Alberta, Canada, which has been a testing site for  innovative passageways to mitigate the effects of roads on wildlife.  The Trans-Canada Highway bisects the park, but a range of engineering mitigation measures—including a variety of wildlife underpasses and overpasses—has helped maintain large mammal populations for the past 25 years and has allowed the gathering of valuable data about wildlife crossing structures.

Urgency and Payoff

Existing roadways often interrupt wildlife passage from one area to another for breeding,
feeding, or general individual movement. There is considerable potential for additional
disruption to wildlife passage from planned roadway construction and highway improvements.
Lack of suitable crossing opportunities for wildlife can lead to serious consequences to wildlife
populations and has created a safety hazard for motorists.

Wildlife crossing systems allow animals to cross roadways with reduced hazard to
wildlife and motorists. The development of wildlife crossing systems often takes into
consideration the placement of fencing and vegetation to channel wildlife to crossings, the
identification of appropriate locations where animals are believed to need to cross, and the type
of crossing facility (culvert, underpass, overpass, at a grade crossing with dynamic warning signs
for motorists). There is potentially a wide variety of wildlife crossing systems that could be
installed. The problem lies in the type of systems that are most effective. Research is needed to
determine the most efficient and cost-effective methods of providing safe crossings for various
species of wildlife.

Suggested By

Transportation Research Board 2002 Environmental Research Needs Conference Notes

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