Millions upon millions of wild animals are killed on our nation's highways every year. Some scientists estimate that humans kill more wild animals with their cars than with any other instrument, including guns. Most animals are members of relatively common species; others are rare, and vehicle-caused mortality is a serious threat to their recovery.
The damage that highways inflict on wildlife is not limited to direct mortality. It starts with the destruction of habitat, and continues with the construction of the road itself, which causes more wildlife mortality. Chemical and physical alteration of the surrounding environment and introduction of potentially invasive species accompany construction and use of roads. Once roads are constructed, development often follows, further degrading habitat. Roads in rural and remote areas allow humans access to previously undisturbed habitats and the plants and animals they harbor.
Perhaps the most serious of all the negative effects on wildlife is the highway's fragmentation of habitat. Fragmentation confines wild populations to areas too small for their needs or forces animals to attempt road crossings to locate food, cover, nesting sites, and mates.
Reconnecting Habitats
A number of European countries have taken the lead in reconnecting wildlife habitats fragmented by roads, and by doing so, are protecting both wildlife and road users. In these countries, dozens of specifically designed overpasses have been constructed to funnel wildlife across major highways. Some are designed just for wildlife and contain small ponds, wetlands, and fruiting shrubs. Other overpasses provide for both wildlife and local traffic.
In creating these overpasses, engineers and wildlife managers utilize earthen berms, wooden walls, or plastic sheeting along the outside rails to shield wildlife from the disturbances of the vehicles below. The habitat that extends from end to end is carefully managed to increase the likelihood that animals will find and use the overpass. As with all wildlife passage structures, well-maintained fences along the highway rights-of-way are critical to guiding wildlife to the structures while restricting their access to the highway itself.
European efforts to protect wildlife also commonly involve the construction of underpasses, amphibian tunnels, and tunnels for small mammals such as otters, hedgehogs, and badgers. The more than 600 tunnels installed under both major and minor roads in the Netherlands have helped to substantially increase population levels of the endangered European badger. Placement of the structures is critical: Animals will not use passages that are not placed along existing habitat corridors.
Fourteen European countries are currently cooperating to map wildlife habitats, in part to determine how best to connect these remaining habitats in this densely populated region. Helping wildlife cross roads that bisect remaining natural lands is an important component of this collaborative effort.
U.S. Efforts
What does all this have to do with the United States? Relatively few overpasses and underpasses currently exist in this country. However, it's critical that state and federal highway planners increase their knowledge of passageway placements and design, and to understand how other countries have made wildlife passages a routine part of each highway project.
To this end, the Federal Highway Administration and the American Association of State Highway and Transportation Officials cosponsored a study tour of five European countries during the fall 2001, for the purpose of bringing back information to enable this country to undertake a similar effort. A plan to implement the findings is now available.
Success will rely on citizens demanding that federal law be changed to ensure that wildlife passages are considered and, where needed, incorporated into every highway construction and improvement project. Even in urban and suburban areas in which most wildlife habitat has succumbed to strip malls and housing developments, there is a need to connect stream valleys, parks, and other open space for wildlife and to provide them safe passage across the roads in their habitats.
