U.S. Geological Survey

Transportation ecology is a newly devel-oped science that focuses on the interac-tions of organisms and the environmentwith transportation infrastructures and vehicles (1). Amajor goal is to understand the effects of roads onwildlife populations and the effectiveness of measures to assist wildlife over and under roads— to prevent collisions with vehicles and to help wildlife move across the natural landscape. The practices and science to accommodate wildlife along transportation corridors aim to main-tain safety and ecological integrity. In the past, trans-portation systems often were built with little regard for the need of wildlife to move. As wildlife–vehicle collisions with large animals, such as deer and moose, became more of a problem, the safety issues of wildlife on the road began to be addressed, mainly by fencing roads and installing wildlife crossings. As the ecological effects of roads on wildlife and fish populations and on ecological processes such as water movement were identified, additional mitiga-tion measures were developed to help wildlife, fish, and water move under and over roadways. With improved understanding of these effects—and of the cost and efforts to mitigate these effects—planning for ecological systems and their inhabitants is becoming part of long-range planning for trans-portation, to avoid, minimize, and reduce the costs instead of waiting until later on in the project stage. Most states have begun accommodating wildlife and fish along transportation corridors, with hun-dreds of terrestrial crossings and thousands of aquatic crossings. The ecological and safety reasons are clear, and trends are emerging in themitigation of the effects of roads on wildlife across North America. Safety Concerns Safety is themost important wildlife-related concern for transportation agencies, but more than ever before, transportation planning and projects are tak-ing into account the ecological effects of roads and vehicles on multiple species. More than 1.5 million wildlife–vehicle collisions occur annually in th