Overpasses and underpasses for migrating animals may reduce collisions with automobiles

In the western United States, mule deer and pronghorn (animals that are similar to antelopes) undergo annual migrations that place them and drivers at risk for collisions when the animals cross busy roadways. A new study evaluated overpasses and underpasses as alternative routes for the animals during migration.

The Wyoming Department of Transportation recently installed 6 underpasses and 2 overpasses along 20 km of US Highway 191 in western Wyoming. Over 3 years, researchers documented 40,251 crossings of the highway by mule deer and 19,290 crossings by pronghorn. Of those highway crossings, 79% of mule deer moved under, whereas 93% of pronghorn moved over the highway.

Wildlife-vehicle collisions were reduced by 81% following construction of the overpasses and underpasses. Pronghorn-vehicle collisions were completed eliminated while mule deer-vehicle collisions fell by 79%.

"This work highlights the importance of species-specific preferences to highway crossing structures. When properly designed and located, crossing structures can improve the safety of motorists and habitat connectivity for migratory wildlife," said Dr. Hall Sawyer, lead author of the Wildlife Society Bulletin article.