As long as there are highways and wildlife, there will be roadkill. Highways are dangerous barriers for all sorts of wildlife.
Therefore, all around the world, local infrastructure planners are increasingly adopting a technique to reduce collisions and make it easier for animals to migrate, mate, eat, and survive: wildlife overpasses.
Animal crossings are popular all over Europe, with the first crossing originating from France in the 1950s.
They are designed to help animals travel safely under and over busy highways, and engineers try to blend them in with nature, increasing the likelihood that animals will use them.
If significantly invested in, wildlife under- and overpasses greatly reduce collisions on the highways, save animals and reduce the financial burden to humans.
The National Highway Traffic Safety Administration reports that in the United States, about two hundred people die in over one million car collisions every year, and these numbers are on the rise.
Rob Ament, the road ecology program manager at the Western Transportation Institute (WTI) at Montana State University says that over the most recently reported 15-year period, wildlife-vehicle collisions have increased by 50 percent, with an estimated one to two million large animals killed by motorists every year.
On the other hand, he explains that crossings and fencing that guide animals under and over highways could lead to reductions of 85 to 95 percent.
These collisions are additionally expensive when accounting for vehicle repair, towing, carcass disposal, human injuries and death, and investigation of the accident by local authorities.
For instance, according to a paper from the WTI, an elk-vehicle collision costs an average of $25,319, a deer-car collision is about $8,190, while moose-vehicle collisions cost $44,546.
Pulitzer Center grantee Robert Chaney explains that hitting an animal is the number one or two cause of vehicle damage listed in the Forest Service annual reports.
Animals in danger of becoming roadkill are deer, bears, bobcats, and turtles, among others. In the United States, there are 21 threatened and endangered species whose very survival is threatened by road mortalities, including bighorn sheep in California, Key deer in Florida, and red-bellied turtles in Alabama.
Overpasses are important in the western portion of North America, where teeming wildlife corridors are intersected by long roads. Fences are used to direct the animals toward the safe passages.
One of the most looked-to examples of successful wildlife overpasses is in Banff, over the Trans-Canada Highway. Its effectiveness has encouraged the construction of many crossings like that there over the last two decades. Namely, in just one two-mile stretch, wildlife-vehicle crashes reduced from an average of 12 a year to 2.5, reducing costs of crashes by 90 percent—over $100,000.
Yet, the success of an animal crossing depends on multiple factors, the most important being in-depth research to determine what kind of crossing would be beneficial to each animal, usually linked to their natural habitat.
With every project, researchers learn more about how animals interact with the passageways, and apparently, different species prefer different types of crossings.
Tony Clevenger, a senior research wildlife biologist at WTI, has been monitoring wildlife at Banff’s six overpasses (and 38 underpasses) for more than 17 years. He concluded that while deers, elks, grizzly bears, and moose prefer big, open structures, cougars and black bears prefer smaller, more constricted crossings, with less light and more cover. This informed the landscaping on the Banff crossings.
Even though overpasses are generally preferred over underpasses, they have certain flaws, like an increased risk of animals entering other animals’ territory, and the little protection provided by the fence, as they can sometimes veer around it and back into traffic.
Clevenger also adds that the roadkill rate at the ends of the fences is high, because the animals either go one way into the overpass or go to the other end and escape around it, and tend to get hit there.
Overpasses are more expensive than underpasses, so many cities prefer underpasses. The use of underpasses is spreading too, and they pass beneath highways to assist shyer and smaller animals.
These passageways are compact and are also serving aquatic species, like the one in Washington state, which links streams and wetlands back to the Yakima River, to help salamanders, reptiles, and fish.
Richard Forman, an ecology professor at Harvard suggests that these wildlife crossings should be involved in the design process earlier. He says that there is always a strategic moment in a road construction project when a wildlife structure can be included.
As we build more and more highways get around the world to satisfy our appetite for concrete, we cut off wildlife, and we contribute to the increased number of animal-vehicle collisions will occur. Therefore, these crossings can effectively reduce the harm.