Impact of Wildlife Crossing Structures on Wildlife–Vehicle Collisions

Abstract

This paper examines whether wildlife crossing structures reduce the number of wildlife–vehicle collisions. Using Washington state crash data from 2011 to 2020, I employed a difference-in-differences methodology at the year level on each of 13 observed wildlife crossing structures in Washington. The treatment area consisted of wildlife–vehicle collisions within 10 mi of a wildlife crossing structure, and the control area included wildlife–vehicle collisions that were 60 to 70 mi from the same wildlife crossing structure. I found evidence that wildlife crossing structures resulted in one to three fewer wildlife–vehicle collisions on average per mile per year. The marginal treatment effect also held within a 5-mi treatment area, a 15-mi treatment area, and when controlling for the presence of other structures within the baseline of a 10-mi treatment area. However, the collision reductions were more consistent among wildlife bridges than culverts, suggesting that not all wildlife crossing structures have the same effect in reducing accidents involving wildlife. Using a back-of-the-envelope approach, each wildlife crossing structure yielded annual benefits of $235,000 to 443,000 in 2021 U.S. dollars.