STUDY: Wildlife Bridges Over Freeways Reduce Animal-Vehicle Collisions By up to 95%

May 16, 2019 at 1:57 pm

Wildlife crossings save the lives of endangered animals and humans

Between 1 and 2 million large animals are killed by motorists every year, according to the Western Transportation Institute.

Most of those are wild animals attempting to cross the road to migrate or find food in what was once their unimpeded range.

There are 21 species that have been listed as threatened or endangered species specifically because of highway mortalities, including Key deer in Florida, bighorn sheep in California, and red-bellied turtles in Alabama.

Highways cut wild animals off from their seasonal migration routes, their food sources and a diverse gene pool, leading to inbreeding, weak offspring and potentially extinction.

Even when animals don’t have safe ways to cross highways, many species will try anyway, including this mother black bear and her cubs in Alberta, Canada. CREDIT: Barret Hedges

“Localized extinction happens when populations can’t find each other, and if they don’t have genetic variability, they will blink out—especially low-mobility species in old-growth forest,” Patty Garvey-Darda, a wildlife biologist with the U.S. Forest Service told National Geographic.

Collisions with animals hurt people too. Around 200 humans are killed each year in over a million such accidents, and billions of dollars are spent on medical bills, car repairs and roadside assistance.

How Wildlife Bridges Help

The Trans-Canada Highway wildlife crossings in Banff National Park, CREDIT: Joel Satore for National Geographic

Wildlife over- and under-passes have been remarkably effective around the world at preventing collisions and restoring populations of endangered animals.

Studies of native species in Floridabandicoots and wallabies in Australia, and jaguars in Mexico demonstrate this.

“You can get reductions of 85 to 95 percent with crossings and fencing that guide animals under or over highways,” Rob Ament, road ecology program manager at the Western Transportation Institute told National Geographic.

Wildlife bridges and tunnels have been popular in Europe since the 1950s, and are now becoming popular worldwide.

(See pictures of the underpass in Kenya reuniting elephant herds.)

Over-crossings look a lot like regular overpass for cars, except they are landscaped with native plants to entice native animals.

Fencing directs migrating pronghorn antelope in Wyoming over the highway instead of across it at Trapper’s Point. CREDIT: Joe Riis

Under-crossings are tunnels under highways that help smaller, shyer animals from gold monkeys and pumas in Brazil to water voles in London.

A wildlife bridge over the Snoqualmie Pass in the Cascades in Washington State is still under construction, with native flora set to be planted in 2020, but deer and coyotes are already using it.

A total of 20 over- and under-passes being built in the area will soon allow bears, mountain lions, pika, and even trout to traverse what was once an impenetrable barrier.

“Grizzly bears, elk, deer, and moose prefer big structures that are open,” says Tony Clevenger, a wildlife biologist at WTI , who monitors 6 overpasses and 38 underpasses  at Banff National Park, where accidents have been reduced by 90 percent.

“Cougars and black bears prefer smaller, more constricted crossings, with less light and more cover.