very year, there are thousands of collisions between vehicles and wildlife on highways throughout the U.S. Northern Rockies. These collisions are often lethal for animals, and come with high societal costs for people. In fact, recent research found that the societal costs of hitting a deer (loss of wildlife, carcass removal, vehicle repair, medical, police, ambulance, etc.) is $8,000 per accident, while for moose those costs climb to a whooping $30,000. The remedy for this threat to wildlife and society is simple – we need to make our highways safer for wildlife to cross.

While this is easier said than done, the new science of road ecology has given safe passage practitioners a better sense of how to accomplish this task. Across the country, practitioners continue to experiment with a variety of structures that can to provide safe passages for wildlife. However, as with many things in life, the most effective solution – in this case, overpasses and underpasses large enough to be used by all sizes of wildlife – comes with the highest price tag. Given that these larger structures are more difficult to fund, if need be, we can start with less expensive options such as “retrofitting” existing highway structures or building smaller new crossing structures. “Retrofitting” refers to the addition of new features to existing structures, such as adding fencing to funnel wildlife under a bridge.

A “Good Start” Approach: Using Existing Highway Structures for Wildlife Crossings

A Red Fox uses a drainage culvert under U.S. highway 287/26 east of Grand Teton, National Park. Photo courtesy of the Wyoming Department of Transportation.

Highways often have pre-existing structures that are used by wildlife, even though the structure was never intended for that purpose. These structures range in size from three foot pipe culverts to large highway bridges over rivers, ravines, or railroads. The most commonly used existing structures are round or elliptical culverts constructed for draining water beneath highways. Foxes, rabbits, pine marten, and other small animals commonly use these small culverts. Larger round, elliptical, or box culverts that channel creeks beneath highways are often used by black bear and other medium sized animals. The still larger “underpasses” that exist beneath highway bridges allow all sizes of wildlife to pass beneath them.

Often we can “retrofit” an existing highway structure so that it can better serve as a wildlife crossing structure. Retrofitting existing structures includes creating a more natural appearance by planting vegetation that is similar to the surrounding habitat and by removing rip-rap, livestock fencing, equipment, bright pieces of metal, boxes, construction material, or other jarring objects.

One of the most common “retrofits” is to construct fencing that funnels animals into the structure, while keeping them off the highway. Even with fencing, and despite our best efforts, animals sometimes find their ways onto the highway. In those situations, fencing that was meant to keep wildlife off the highway unfortunately keeps them on it. In these cases, animals need “escape ramps” or “jump-outs” that allow them to “through” the fencing and off the highway.

These less expensive retrofits are an important first step – a good start – in providing wildlife a way to safely cross a highway, thus making that section of road safer for people and wildlife.

“Made for Wildlife” Crossing Structures: Building New Underpasses and Overpasses

Wildlife overpasses like this one in Banff National Park, Canada, cost a lot, but will be crucial for providing wildlife safe passages in the Northern Rockies. Photo by Reno Sommerhalder

While pre-existing highway structures can go a long way toward reducing accidents between wildlife and people, they do have limitations. Many of the structures outlined above are not big enough to be used by larger wildlife (deer, elk, moose, etc). Additionally, there may not be enough pre-existing structures to provide safe passages for wildlife over a longer stretch of highway. In these situations, the best thing we can do to protect wildlife and motorists is to build a number of overpass or underpass crossing structures that are big enough for all wildlife to use. “Made for wildlife” crossing structures, such as the ones in Banff, are the most effective because they accommodate the broadest range of species.

For example, in Canada’s Banff National Park, two vegetated wildlife overpasses and twenty-two underpasses were constructed in 1996 along twenty-eight miles of the Trans-Canada Highway. Fencing was erected along the entire stretch to funnel wildlife towards the structures. Since then, researchers have documented that more than 72,000 animals have crossed these structures, including wary grizzly bears, wolves and cougars. In addition, collisions with moose, elk, deer, and bighorn sheep along this twenty-eight miles have been reduced by 96 percent.

American Wildlands supports using both pre-existing highway structures and building new wildlife crossing structures, because we believe it is a strategy that will work best in making our highways safer for wildlife and motorists alike.

Video of grizzly and black bear, cougar, elk, and deer using underpasses in Banff National Park can be viewed here