100 Million Crabs Get Their Own Bridges: 12 Wildlife Crossings That Animals Actually Use

Banff National Park in Canada has 44 wildlife crossings over and under the Trans-Canada Highway, six overpasses and 38 underpasses, plus 82 km, about 51 miles, of fencing. Parks Canada calls it the most numerous and varied set of wildlife crossings in the world.

Eleven species of large mammals used them more than 150,000 times between 1996 and 2012. Collisions between vehicles and wildlife dropped by more than 80%, and by more than 96% for elk and deer. Wary grizzly bears took up to five years to start using the crossings.

On Interstate 25 between Castle Rock and Monument, south of Denver, Colorado added fencing, underpasses and a $15 million overpass that officials call the largest of its kind in North America. It spans six lanes of traffic.

Wildlife-vehicle collisions fell by about 85% a year on average from 2022 to 2024, and 91% in the final year studied, thanks to a whole system of fences, tunnels and the bridge. Cameras have recorded elk, mule deer, rabbits and northern leopard frogs on the overpass, and pronghorn crossing to the west side of the highway for the first time in decades.

Utah’s Department of Transportation finished a wildlife overpass over Interstate 80 at Parleys Summit, east of Salt Lake City, in 2018. It is 50 feet wide and 320 feet long and crosses six lanes of traffic. In the two years before it was built, 106 collisions between vehicles and animals were recorded there.

Cameras on the bridge’s guardrails have filmed deer, moose and elk, plus black bears, bobcats, cougars, coyotes, yellow-bellied marmots and porcupines, using it sooner than experts expected.

Every year, after the first rain of the wet season, the red crabs of an Australian island in the Indian Ocean leave the forest and march to the sea to breed. The island’s red crab population is estimated at about 100 million, and they have to cross roads on the way.

Rangers close sections of road during peak season, sometimes at short notice, and the national park has built crab bridges over the roads so the crabs can climb over the traffic instead of walking into it. The march usually starts in October or November.

In July 2025, California started building its first wildlife overpass, a $20 million bridge over State Route 97 in Siskiyou County, near the Oregon border, with 8-foot fencing to steer animals toward it. The two-lane highway cuts through a migration route for mule deer and elk.

In late May 2026, one of nearly 100 cameras around the site caught three mule deer walking over the unfinished bridge, just 15 hours after the crews had left for the day.

Near Hilversum in the Netherlands, the Natuurbrug Zanderij Crailoo runs 800 meters, about half a mile, over a provincial road, the Hilversum—Bussum railway line, a rail company’s business park and a sports park. Dutch broadcaster BNNVARA calls it the longest nature bridge in the world.

It is 50 meters wide at its narrowest point and up to 150 meters wide with its slopes. It opened on May 3, 2006, reconnecting nature areas that roads and rails had cut apart.

One rainy night each spring, once the evening temperature rises above 40°F, hundreds of spotted salamanders in North Amherst, Massachusetts, cross Henry Street to breed in pools on the other side. In the early 1980s, residents formed a bucket brigade and carried them across by hand.

In 1987, tiny tunnels were installed under the road, about 10 inches high and 6 inches wide, with slotted tops to keep them damp. About 100 to 200 animals use them each year.

In 2013, Singapore finished the Eco-Link@BKE, a 62-meter planted bridge over the six-lane Bukit Timah Expressway that reconnects two nature reserves. It was built for animals like the Sunda pangolin, a shy, scaly anteater that is critically endangered.

At least one pangolin crossed it every month from October 2014 to December 2015. In early 2016, a lesser mousedeer turned up in the Bukit Timah reserve, a sign that it had crossed too.

India’s National Highway 44 runs 4,112 km, about 2,555 miles, down the middle of the country. Where it passes the Pench Tiger Reserve, nine wildlife crossing structures were built, including five purpose-built animal underpasses.

A 2019 camera-trap survey found at least 18 species using them, including tigers, wild dogs, sloth bears, civets and leopards.

On Costa Rica’s Caribbean coast, roads and buildings have cut gaps in the rainforest canopy, and a sloth that comes down to the ground to cross is slow and exposed. The Sloth Conservation Foundation strings rope bridges across those gaps, at about $200 each, so sloths, monkeys and other animals can cross the road through the treetops.

Rebecca Cliffe, who heads the foundation, told Bloomberg that in a well-connected rainforest, sloths are “masters of survival.”

Only about 150 critically endangered mountain pygmy possums live on Mount Little Higginbotham in the Victorian Alps of southeast Australia, and the Great Alpine Road splits them into separate groups. To help them mix, conservationists built a tunnel under the road that became known as the “tunnel of love.”

Over two summers, 30 possums were identified using it, often in spring when they wake up from hibernation. They can dash through the nearly 15-meter, about 50-foot, tunnel in 15 seconds, sometimes too fast for the cameras.

In the early 1970s, there were as few as 200 golden lion tamarins in the wild, in the coastal forests of southeastern Brazil. When the BR-101 highway beside the Poço das Antas reserve was widened to four lanes, it cut their forest in two.

A forested bridge, 20 meters wide and planted with native trees, was finished over the highway in 2020. Possums, pumas, marmosets and armadillos already use it, and in April 2026 scientists said they expected the first tamarins to cross within the next year. About 2,500 golden lion tamarins now live in the wild.