How Wildlife Crossings Work
Animals need to move around their habitat in order to survive. Unfortunately, highways often bisect or block the natural paths that these animals use, causing them to get hit by cars and trucks. Wildlife crossings have proven to be one of the most effective ways to reduce wildlife-vehicle collisions and improve habitat connectivity. These structures, which include bridges, underpasses, and tunnels, are designed to help animals safely pass over or under roads without the risk of encountering vehicles.
As road networks expand, wildlife crossings have become an important tool for helping to reconnect fragmented habitats, reduce vehicle-wildlife collisions, and increase biodiversity. Wildlife-vehicle collisions are not just costly for drivers, they also can kill or injure animals. One 2022 study found that crossings—especially combined with high fencing that inhibits animals from stepping onto the roadway—are 83% effective at reducing wildlife-vehicle collisions.
While many people may assume that these crossings and fencing provide predators an easy meal, this is not the case. In fact, the evidence shows that crossings and fencing actually encourage prey species to stay away from roads, as they are more likely to find safe refuge in nearby habitat, where there is a greater chance of finding food and shelter.
For example, the corridors that connect the mountains, wetlands, and forests of the Western United States are home to a variety of big game species such as pronghorn, elk, bighorn sheep, mule deer, and coyotes, plus a range of smaller species including birds, lizards, squirrels, and porcupines. Similarly, the network of six bridges and 38 underpasses built in Banff National Park in Canada have been shown to significantly reduce incidents between wildlife and vehicles, particularly for grizzly bears, which have been able to maintain a large enough population to ensure genetic diversity.
As wildlife populations continue to shrink and humans expand their footprints, a growing number of animals are encountering deadly traffic collisions. And while there are numerous factors that can contribute to these fatal accidents, the single most common reason for animal-vehicle collisions is that the animals are trying to cross the road in the presence of vehicles.
The good news is that the solution to this problem is relatively simple: wildlife crossings. By incorporating these structures into road and highway construction and renovation projects, wildlife-vehicle collisions can be greatly reduced. These structures—which can include underpasses, tunnels, and culverts—are specifically designed to guide animals over or under roads without the risk of crossing directly into them.
While the cost of these structures can be higher than traditional culverts or fencing, they are also considered to be highly cost-conscious and self-funding in the long term. This is why many ecologists and conservationists are advocating for their inclusion in linear infrastructure design.
These crossings can be as simple as a culvert or as complex as an underpass, and their designs should be tailored to the local species that will use them. For instance, a small tunnel might work best for amphibians and reptiles, while an underpass that is wide enough to accommodate large mammals such as moose and mountain lions could be needed in Alaska or British Columbia.
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