The rapid increase in animal-vehicle collisions on U.S. roadways is a growing concern in terms of human safety, property damage and injury costs, and viability of wildlife populations. Wildlife crossing structures are gaining national recognition by transportation agencies as effective measures to reduce animal-vehicle collisions and connect wildlife habitats across transportation corridors. In Virginia, white-tailed deer and black bear pose the highest risk. This one-year study was conducted to monitor various underpass structures in Virginia to determine the structural and location attributes that make a crossing successful in terms of use by large mammals. The underpasses, most of which were not specifically designed as wildlife crossings, consist of box culverts and bridges of varying sizes. Remote cameras installed at seven underpass sites in Virginia have recorded more than 2,700 wildlife photographs and documented 1,107 white-tailed deer crossings in the most heavily used structures. Underpasses with a minimum height of 12 ft were successful at facilitating deer passage. Such structures were also heavily used by a variety of wildlife species, including coyote, red fox, raccoon, groundhog, and opossum. Structures with drainages that mimic natural waterways can encourage use by a diversity of terrestrial, semi-aquatic, and aquatic species. This report provides guidance in choosing cost-effective underpass design and location features that are necessary to consider to increase motorist safety and habitat connectivity. The findings also demonstrate that if only a minimal number of deer-vehicle collisions is prevented by an effective underpass, the savings in property damage alone can outweigh the construction costs of the structure.

Transportation agencies across the United States are under increasing pressure to minimize or avoid impacts of transportation projects to important wildlife habitat. With new road construction and lane additions, habitat fragmenta¬tion is becoming more pronounced and its effects are increasingly evident. Transportation projects are often planned, designed, and funded before taking important habitat considerations into account, which can lead to expensive delays and lawsuits.

Wildlife linkage or corridor analyses are being conducted in an increasing number of states, and more transporta¬tion agencies are using this information during the planning of proposed road projects. The Virginia Department of Conservation and Recreation’s Natural Heritage Program is creating a GIS tool, the Virginia Natural Landscape Assessment (VANLA) that identifies large patches of natural landcover (habitat cores) and the habitat linkages con¬necting these areas (landscape corridors). This mapping project can be integrated into the Virginia Department of Transportation’s (VDOT) existing GIS applications for access by staff involved with transportation planning and environ¬mental scoping activities. Analyzing a proposed project in these early stages of project development will allow VDOT to identify important natural resource areas and wildlife corridors to avoid or for which mitigation may be necessary. This can result in fewer project delays, promote collaboration between VDOT and state natural resource and regulatory agencies, and meet the directives of the new habitat conservation provision in the federal transportation legislation. In addition, basing certain project decisions on a project’s location relative to a wildlife corridor can decrease the risk of animal-vehicle collisions.