Wildlife crossings are more than custom-made ways to prevent roadkill: They can play a key part in stopping the biodiversity decline worldwide.

Drive south on U.S. Route 441 from Gainesville, Florida, and you’ll come across vast expanses of wetland. In the morning, the spiky purple flowers of pickerelweeds bloom as the sun rises over the horizon of Paynes Prairie Preserve State Park. Come sunset, the sky turns into a watercolor of pastels where sandhill cranes fly in search of a place to rest. And lurking among it all, tucked among the grasses and slithering beneath the swampy water, is a who’s-who of Florida’s finest: the American alligator, mole salamander, Florida softshell turtle and green anole lizard.

But divert your eyes to the pavement barreling by, and you’re bound to see casualties. Frogs, salamanders, alligators and other creatures risk their lives crossing the highway while on the hunt for dinner or when traveling to mate and lay eggs. For years, thousands of animals were killed along the route, and the road gained a well-earned reputation as a death zone.

So to prevent the high rate of animal casualties, the Florida Department of Transportation in 2000 built eight wildlife culverts for the animals to crawl through.

It worked.

A year after installing the underpasses, mortality rates had dropped drastically, from 2,411 to 158 animals — a decrease of 93.5 percent.

The tunnels underneath U.S. 441 are known as wildlife crossings, and they allow animal populations to safely migrate across habitats without the constant threat of speeding vehicles. Each day more than 1 million vertebrates are run over in the United States, and an estimated 1 to 2 million collisions happen every year between large animals and cars.

But the crossings, which can also take the form of under- and overpasses, serve a more important purpose than keeping individual animals alive and your car dent-free: Each wildlife crossing connects islands of isolated habitats intersected by roads, bridges and other manmade structures. Florida’s efforts are part of a bigger push by conservationists to protect wildlife corridors, or stretches of habitats that connect populations of animals, which in turn helps protect the region’s biodiversity.

After a recent United Nations report found that roughly 1 million species worldwide are threatened with extinction, constructing wildlife crossings has become even more urgent. After all, the main drivers of extinction are man-made (think exploiting natural resources, climate change and pollution). Shouldn’t the solution also be?

Ron Sutherland, the chief scientist at the Wildlands Network, an organization that fights species extinction, highlighted the ways habitats are currently fragmented: Roads often cut across wildlife corridors, agriculture has cleared tremendous amounts of habitat, and urban sprawl keeps, well, sprawling. The goal of wildlife crossings is to reconnect habitats with their native animal populations. Doing so allows for gene flow, an essential ingredient of biodiversity. Without different populations to mate with, animals are forced to inbreed, leading to the eventual collapse of their population.

“We really do see wildlife corridors and road crossings as a core solution for stopping the biodiversity extinction crisis,” Sutherland said in an email.

SAVING MONEY — AND BIODIVERSITY

If protecting species isn’t enough, Sutherland emphasized the financial incentive to build crossings. The price of hitting an animal can cost motorists and taxpayers a pretty penny — deer collisions run about $8,000, elk an average of $25,000, and moose upward of $44,000 when factoring in things like human injury and vehicle repair, according to the Western Transportation Institute.

“So even a million-dollar wildlife road crossing structure can pay for itself in public benefits over the course of just a few years,” Sutherland told NationSwell. “They’re in the public interest, and they’re in the interest of saving biodiversity.”

From salamanders in Massachusetts to cougars in California, researchers have recorded lower collision rates and high animal usage after crossings are built.

Perhaps the most popular and well-studied example is the network of wildlife crossings at Banff National Park in the Canadian Rockies. In the 1980s, due to increased traffic on the Trans-Canada Highway, officials expanded the road from two lanes to four. Transportation planners and scientists drafted a solution to minimize the effect the expansion would have on wildlife. From 1996 to 2014, six wildlife overpasses and 38 underpasses were built along the border of Banff and Yoho national parks.

Subsequent studies showed that the designated crossings reduced animal-vehicle crashes by 80 percent. Since 1996, an estimated 150,000 animals have used the crossings, including grizzly bears, wolves, coyotes, cougars, moose, elk and deer.

Wyoming is home to another successful project. The Path of the Pronghorn, a 170-mile wildlife corridor, gives pronghorns, ungulates and other species a safe way to cross a major highway as they migrate each spring to give birth and seek out the freshest, most nutrient-rich food. After two wildlife overpasses and an underpass were built, animal-vehicle collisions were reduced by 70 percent.

Wildlife crossings are achieving their goals, said Sutherland. “Species are moving across them, and the economic data indicates [the crossings] basically pay for themselves if you put them in the right places.”

PROTECTING HABITATS THROUGH POLICY

But crossings are just one stick in a bundle of solutions, said David Willms, senior director for Western Wildlife and Conservation at the National Wildlife Federation. He stressed that it’s challenging and costly to build enough of them to completely mitigate the effects of new roads and other construction projects.

It’s clear that crossings work. But just as important is passing legislation that protects habitats before roads are built and wildlife is disconnected. For example, the Wildlife Corridors Conservation Act, introduced in Congress in May, would establish, protect and maintain corridors at the local, regional and national levels. If passed, it would establish a science- and data-driven system of designation for land that would prevent activities like oil drilling and mining. It would also create funding for wildlife crossings and other projects.

Laws protecting wildlife are already being passed at the state level, including in New Mexico and New Hampshire. A handful of other states are considering similar legislation.

“We have the technology now to identify those spots, and we have the case studies now to show that those crossings work,” said Willms. “Those are two bigs pieces of the puzzle. Now you just need the political will to get the funding in place to get more of them.”

Because corridors often overlap with publicly and privately owned lands, other solutions rely on the support of landowners — for example, working with farmers in a way that protects the wildlife habitats on their lands without affecting their business operations. “I haven’t found a landowner yet that doesn’t recognize the value of these wildlife corridors,” Willms said.

Sutherland said it’s an issue that people across all regions and political beliefs are supporting. In more conservative western states, “there’s been an increasing recognition that elk, mule deer, pronghorn antelope and other species need to migrate in the interest of saving biodiversity.” In response, those states are working to identify and protect the large expanses of land that still exist. In the east, where habitats are particularly broken up, he admits the approach is more piecemeal. In those states, Sutherland said, it’s more a question of, “Can we stitch things back together again into a network of habitats that would be enough to save species?”

Still, Sutherland has faith. At the Wildlands Network, he and other conservationists are working to create the Eastern Wildway, a habitat network that extends from Florida to Quebec. “It is a grand and ambitious plan that would take decades to achieve, but the benefits for nature and people would be immense,” Sutherland said. A stretch of land like this would protect thousands of species.

But Willms countered that there often isn’t enough research to know what specific routes and corridors need protection.

For example, a key migration corridor for mule deer in Wyoming was accidentally discovered just seven years ago. Researcher Hall Sawyer believed a herd of mule deer was residential. He put GPS collars on a few deer and discovered that the animals were actually migrating a grueling 150 miles each year, from the Hoback region near Jackson down to the Red Desert. On the journey, the deer were met with man-made obstacles like fencing, roads and urban sprawl. That data helped push the Wyoming Game and Fish Commission to designate the area as a migration corridor, which informs land management decisions such as adding animal-friendly fencing and creating protected areas.

“We’re closer to the beginning than we are to the end, because there’s just so much more research that can be done,” Willms said. “These crossings are invaluable and certainly scalable.”

CORRECTING FOR A CHANGING CLIMATE

Part of that research involves understanding how climate change will impact animals’ migratory paths. Historically, species respond to changes in the climate by moving and migrating to other areas in search of their preferred conditions.

Climate migration has been on the radar of scientists for decades, said Sutherland, but the issue has become more central as the pace of climate change accelerates. “Not only are humans causing climate change to happen much faster now, but we’ve broken up the landscape into small pieces where there are not very many opportunities for species to migrate like they used to.”

That means that in addition to protecting existing wildlife corridors, conservationists and their allies need to find ways to reconnect swaths of land that have been siphoned into ever smaller slices.

According to Sutherland, it’s not enough to simply fight climate change in an effort to stymie it. “It’s already happening,” he said, “and so we need a network of habitats to allow for that adaptation.”

More: Montana’s Progressive Road Design Accommodates Wildlife