Why Wildlife Crossings Work

Over the course of a single day, people drive 4 trillion miles on America’s roads. This vast expanse of asphalt is not just a threat to drivers; it’s also an obstacle for wildlife and an impediment to ecosystem resilience. Wildlife crossings—bridges and tunnels built to allow animals to safely traverse a road or railroad line—are an innovative solution to this problem, and studies across the globe show that they work.

A recent study found that wildlife crossings—which are designed to fit into the natural environment—are 83% effective at preventing vehicle-wildlife collisions (VWCs) and help keep populations of animals healthy. They’re especially important for vulnerable species, like the reintroduced cougars in Montana, black bears in Alaska, and grizzly bears in Canada, which require wide-ranging habitat in order to find mates, maintain genetic diversity, and survive.

The most effective wildlife crossing structures are usually covered in native vegetation to make them look and feel like a natural part of the landscape. They are designed for the specific species they’re intended to serve and, in many cases, work best in conjunction with highway fencing that funnels wildlife toward the structure. Prior to building a crossing, scientists often observe a highway for several months to understand how and where animals move in the area and then identify the best location for the structure.

Depending on the species and project, wildlife crossings can range in size from a small culvert to a six-lane bridge. They can be installed in new construction or in existing roadways. Ideally, they’re placed where movement corridors for the focal species intersect or are blocked by dominant topographic features, such as ridgelines and riparian areas. For more details please visit wildlifecrossingswork.com

Once in place, a crossing is often very well-used and can reduce the risk of collisions for both people and wildlife. A series of 44 bridges and tunnels constructed on the Trans-Canada Highway through Banff National Park, for example, has helped cut mammal deaths caused by vehicles by more than 80%.

But even more importantly, wildlife crossings connect wild animal habitats, which is a key part of “rewilding” and essential to ecosystem health. By allowing migratory animals like mule deer to move through their territory and ensure that predators such as cougars can find the mates they need, these vital passageways help prevent VWCs, stabilize population sizes, and foster a healthy ecological balance.

The best way to protect wildlife and motorists is by implementing a national wildlife crossing network, including land management agencies and other partners. This would ensure that the wildlife crossings are part of a larger corridor network and not just “ecological dead-ends.” To do this, federal agencies should prioritize funding to build wildlife crossings, working with state and local governments to ensure that the necessary habitat is available to support their construction.