Wildlife crossings don’t just save lives, they save money too

Wildlife structures built in Washington state have not only saved precious biodiversity but also enabled the saving of millions of dollars every year, an economic analysis conducted by researchers at Washington State University (WSU) has revaled.

Wildlife crossings have often been proposed and constructed to preserve wildlife and help them escape predators and forest fires. In the state of Washington, there are currently 22 bridges and underpasses built solely for wildlife, with half of them found in Kittitas County, where the manmade road bisects the Cascades, a habitat for many animals.

The cost of these constructions varies on the complexities involved. A tunnel-like underpass can be constructed for about $500,000, but a broad bridge for herds to cross over can cost upwards of $6 million. Wisnu Sugiarto, a doctoral student in economics at WSU, decided to check if there were also economic benefits of these structures.

Sugiarto analyzed collisions from the Washington State Department of Transportation in 13 areas where underpasses or bridges were built. By studying the data for periods between 2011 and 2020, Sugiarto could compare collisions before and after these structures were built. To compare, he also used an area of the state where no structures were built.

What did the researcher find?

His research revealed that there were more than 1,600 wildlife-vehicle crashes every year in the state, with about 10 percent resulting in human injury. Some crashes also led to human deaths. Most of these crashes involved safe drivers who were sober and driving without distractions when the crash occurred.

The study also found that there were 1-3 fewer wildlife-vehicle collisions per mile each year in a 10-mile radius around each wildlife crossing. More significant reductions in collisions were found around bridges.

Deer were the most common animals involved in vehicle collisions, each costing about $9,000 on average. Roughly calculated, each structure saved $235,000 to $443,000 every year. Similar evidence has been found through studies conducted in North Carolina, Utah, and Wyoming by other researchers.

"From a driver's point of view, they may choose to drive safely, but still, unfortunately, there are animals that cross the road, and they end up hitting them. This shows there’s something we can do about these collisions,” said Sugiarto in the press release. "Decreasing accidents would further reduce unnecessary trauma and also save lives in addition to saving money."

The study relied on official reports required only when the damage is $1,000 or more. Insurance claims could possibly reveal more data and benefits of these structures.

The study also revealed information about animal behavior. Camera traps showed that deer liked to use bridge crossings while predators like bears preferred underpasses.

The results of the study were published in the journal Transportation Research Record.

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.