Use of Highway Underpasses by Large Mammals and Other Wildlife in Virginia

Wildlife crossing structures are gaining recognition by transportation agencies as effective measures to reduce animal–vehicle collisions and to connect wildlife habitats across transportation corridors. For the species that pose the highest risk in terms of animal–vehicle accidents in Virginia, namely, white-tailed deer and black bears, research is lacking on structural and location attributes of effective crossing structures. The Virginia Transportation Research Council began a 1-year study in June 2004 to monitor potential crossing structures and to determine the features that make a crossing successful for Virginia's large mammals. The underpasses, most not specifically designed as wildlife crossings, consist of box culverts and bridges of varying sizes. Remote cameras installed at seven underpass sites have recorded more than 2,700 wildlife photographs and documented 1,040 white-tailed deer crossings in the most heavily used structures. Underpasses with a minimum height of 12 ft were successful in facilitating deer passage. Structures that were suitable for deer passage 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. If even a minimal number of deer–vehicle collisions are prevented by an effective underpass, the savings in property damage alone can outweigh the construction costs of the structure.