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Wildlife crossings stop roadkill. Why aren’t there more?

A better way for animals to cross the road.

Wildlife crossings are structures that facilitate animal movement across roadways. The crossings resemble overpasses and underpasses built for humans and cars, but they’re meant for animal use only.

There are relatively few wildlife crossings in the United States compared with Western Europe and Canada, but here are a few reasons we might consider building more:

Crossing structures make driving safer

Crossing structures drastically reduce wildlife-vehicle collisions. Several studies have shown that mitigation systems involving crossing structures, where they have been installed correctly, have reduced collisions between vehicles and various animal species by upward of 70 percent.

They reconnect wildlife habitats

Besides the risk for roadkill, roads harm animals by fragmenting their habitats and making it difficult to find food, mates, and other essentials of life. If events such as a forest fire damage strain resources on one side of the highway, the effect is even more acute.

In Banff National Park in Alberta, Canada, the dissection of habitat by the Trans-Canada Highway had restricted the movement of grizzly bears. Bear populations were divided into isolated small groups that had fewer potential breeding partners and therefore lacked genetic diversity. After crossing structures were installed, data shows that grizzlies began using them to cross between opposite sides of the highway, and the fragmented population began to reconnect.

A pair of grizzly bears using an animal overpass in Banff National Park.
Tony Clevenger/Parks Canada

They are cost-effective

In addition to protecting the lives of animals and humans, there is another reason we should consider building more crossing structures: They can save money.

In one study, scientists were even able to identify specific thresholds at which crossing structures become a cost-effective way to reduce collisions between vehicles and large ungulates (deer, elk, and moose). They conducted a cost-benefit analysis that computed the average cost of installation with the average life span of the structures, data demonstrating how effective they are in mitigating collisions, and data quantifying the average cost of collisions. The results determined various thresholds at which different mitigation efforts become cost-effective solutions for reducing animal-vehicle collisions.

For example, the analysis determined that the break-even point for installing a mitigation system using underpasses and fencing is 3.2 annual deer collisions per kilometer. That means that installing a crossing system using underpasses will be a cost-effective investment on any kilometer of road where more than 3.2 deer-vehicle collisions occur per year.

Although crossings can save money in the long run, the initial investment is typically several million dollars, which is an expense beyond the budget constraints of many state transportation departments.

But they can be even cheaper

Many crossing structures are built from structural plans designed for vehicular usage. But this approach can include unnecessary design elements that can add to the expense of the project or discourage animal use.

Seeing a need for innovation, a group of scientists, planners, and engineers got together to generate cheaper and more effective designs. They organized a design competition, named ARC Solutions, that encouraged multidisciplinary collaborative design.

ARC Solutions finalist Research Evolve Design (RED) by Janet Rosenberg & Studio.
ARC Solutions

To learn more about the contest and to see the designs that were selected as finalists, make sure to watch the video above. For more Vox videos, subscribe to our YouTube channel.