Study: Wildlife crossing structures in Washington are good for the environment, the wallet

Animal crossing structures over and under roads are good for the environment, good for safety and good for our collective wallet. Those were the findings from a Washington State University economic analysis published in the Transportation Research Record in August.

“Wildlife crossing structures not only benefit the ecosystem but may also improve road safety,” said Wisnu Sugiarto, a WSU economics doctoral student.

In fact, Sugiarto found that the structures save between $235,000 and $443,000 every year per structure. The analysis found there were 1 to 3 fewer collisions involving wildlife per mile, each year in a 10-mile radius around each wildlife crossing in the study. During that same period there were more than 1,600 wildlife-vehicle crashes, with 10% of those leading to human injury or death. WSDOT’s wildlife-collision reports are only required if there $1,000 in damage or more.

Adjusting for construction time and closeness of other structures, Sugiarto examined data related to 13 bridges and underpasses, comparing wildlife-vehicle collisions before and after the structures were built. He also used an area elsewhere in the state with no structures for comparison.

Currently there are 22 wildlife bridges and underpasses in Washington, with half of those in Kittitas County. Those structures range in cost from $500,000 to $6 million, as in the case of the bridges crossing I-90 near Snoqualmie Pass.

When it comes to type of structure, Sugiarto found that bridges seemed to prevent the most accidents, perhaps because deer – the main species involved in collisions – seemed to prefer bridges. And while Sugiarto’s research is the first time anyone has looked at these questions in the Evergreen State, he built on similar research in North Carolina, Utah and Wyoming.

Sugiarto said he was motivated to conduct the study after moving to Washington and learning about the state’s existing wildlife crossings. He began to wonder if those structures, which are largely designed with habitat connectivity in mind, had much impact on vehicle collisions.

“The use of wildlife crossing structures signals a possible reduction in wildlife-vehicle collisions because animals are off the roads,” he wrote in an email. “However, wildlife crossing structures may be constructed in areas that do not historically have many wildlife-vehicle collisions. Their construction may be the result of a focus on wildlife connectivity, rather than motorist safety. In such cases, the presence of structures may not affect the number of collisions. These two opposing reasons also motivated the empirical research presented in the paper.”

Meanwhile, Conservation Northwest – a Washington conservation advocacy organization – has continued working toward installing more crossing structures.

Top of that list? Crossing structures on Highway 97 in the Okanogan Valley, an area that is a animal-vehicle collision vortex. Jay Kehne, CNW’s Safe Passage 97 project manager said addressing connectivity needs and human safety is why it’s an important project.

“On HWY 97 it was very important to the local public that this was not all just about wildlife, they also wanted to know that the money spent would be valuable at reducing accidents and potential harm to people as well,” he said in an email.

In 2021, The Legislature authorized $2.7 million to be used as matching funds for federal grants to continue the project.

“The current plan is to build one to two underpasses and connect them with deer fence south of where the first phase ended,” Kehne said. “All of this is ongoing right now with the Washington State Department of Transportation in charge of obtaining additional grant funding possibly through the infrastructure bill or other avenues. CNW is supporting their efforts with field visits and on the ground input.”