Module 4: Design and Guidance of WVC Mitigations for Large Mammals

Previous 17 of 67 Next

Wildlife Underpasses

Wildlife underpasses are designed primarily to provide connectivity for wildlife species, often in combination with wildlife fencing; however, underpasses are sometimes deployed as stand-alone mitigation measures. When used in combination with wildlife fencing, wildlife underpasses help to reduce road corridor intrusions since the structures provide animals with a safe crossing opportunity. When used as a stand-alone mitigation measure, the reduction in WVCs may be limited to the immediate vicinity of the underpass.

Effectiveness in Reducing Collisions with Large Mammals

The effectiveness of "crossing structures" (i.e. underpasses and overpasses) in reducing large-mammal WVCs has been estimated at 79-97 percent, when used in combination with large-mammal fencing (see Fencing section of this module).

Four different types of underpasses are pictured in these photographs. The types of underpasses pictured in this section serve a wide range of mammal species from small to large. Additional types of underpasses implemented for endangered species are depicted in Module 5 of this training.

Figure: Open span bridge wildlife underpass, approximately 39 ft. wide and 16 ft. high.(Copyright: Marcel Huijser)	Figure: A medium-mammal culvert approximately 6 ft. in width and 5 ft. in height. It is located along U.S. Highway 93, south of Ravalli, MT. (Copyright: Marcel Huijser)
Figure: A large mammal underpass with dimensions, approximately 23-26 ft. wide and 13-16 ft. high. It is located along U.S. Highway 93 south of Ravalli, MT. (Copyright: Marcel Huijser)	Figure: A pipe structure for small to mid-sized animals. These structures are typically 1-2 ft.