Fifty miles east of Seattle, a bridge crosses a steep stretch of Interstate 90 known as Snoqualmie Pass. This is no ordinary bridge, meant for automobiles or pedestrians. Covered in topsoil, boulders, and seedlings, it is intended to convey wild animals from one side of the highway to the other — and it’s working.
Since 2018, when the bridge opened and the first animal, a coyote, scampered over the six lanes below, the structure has carried creatures as large as elk and as small as toads. And it should attract even more users as the seedlings grow into trees and animals acclimate to its presence.
“As we get more shade, it’s going to be different,” Patty Garvey-Darda, a Forest Service wildlife biologist, told Vox during a recent visit to Snoqualmie Pass. “Hopefully someday we’ll see the exact same species up here as we see in the forest.”
The Snoqualmie Pass bridge is one example in a broader category of infrastructure, known as wildlife crossings, that help animals circumvent busy roads like I-90. Crossings come in an array of shapes and sizes, from sweeping overpasses for grizzly bears to inconspicuous tunnels for salamanders. A body of research demonstrates that crossings can reconnect fragmented wildlife populations, while protecting human drivers and animals alike from dangerous vehicle crashes. “This structure is paying for itself because of the accidents we haven’t had,” said Garvey-Darda, as trucks roared by 35 feet below.
The construction of such crossings has never been more urgent. Roadkill rates have risen over the past half-century; today, around 12 percent of North American wild mammals die on roads. And new satellite-tracking and genetic technologies have revealed subtler harms. Busy interstates prevent herds of elk and mule deer from migrating to low-elevation meadows in winter, occasionally causing them to starve. In California, freeways have thwarted mountain lions from mating, leaving the cats so inbred that they’ve fallen into an “extinction vortex.” Wildlife crossings allow animals to find food and each other across sundered landscapes, and help them access new habitats as climate change scrambles their ranges.
But despite crossings’ benefits, they remain scarce in the US. Around 1,000 wildlife crossings currently dot America’s 4 million mile road network. (For comparison, the Netherlands’ road system is only 2 percent as large but boasts over 600 crossings.) The reason for their rarity? Money. The Snoqualmie Pass bridge cost $6.2 million, and even humble turtle tunnels can run up multimillion-dollar price tags. This kind of expense explains why wildlife crossings were once a punching bag for some conservative politicians, who decried animal passages as government waste.
Now that’s beginning to change. Earlier this month, the House passed the INVEST in America Act, a $1.2 trillion infrastructure bill that President Joe Biden is expected to soon sign into law. The bipartisan package earmarks billions of dollars in funding for highway maintenance, broadband internet, and airport upgrades — as well as $350 million for animal-friendly infrastructure like bridges, underpasses, and roadside fences. Although that provision is a tiny slice of the bill, it’s easily the largest investment in wildlife crossings in national history.
These innovations are not only wildly effective at preventing roadkill, they’re also an underappreciated way to protect people. Hundreds of Americans die annually in car crashes with animals, and tens of thousands more are injured. “Whether it’s human safety or habitat connectivity or fiscal responsibility, there’s something in this bill for you,” said Renee Callahan, executive director of ARC Solutions, a group that studies and promotes crossings. “This has become a staunchly bipartisan issue.”
When the US interstate highway system was constructed more than half a century ago, ecosystems were damaged in ways we’re only now beginning to fully understand. Wildlife crossings and other animal-friendly infrastructure help mend that damage, and accommodate the creatures whose lives our highways have disrupted. Even within a bitterly divided Congress, it’s a rare area of consensus. One of the few things uniting some fiscal conservatives with climate-concerned Democrats is a literal bridge.
How wildlife crossings went mainstream
Roads have few equals as a destroyer of animal life. Vehicles claim more wild terrestrial animals — perhaps more than a million per day in the US alone — than any other form of direct human-caused mortality, like hunting, oil spills, or wildfires. And it’s not just common critters like squirrels that get flattened (though we should worry about their welfare, too). At least 21 species are imperiled by cars in the US, and one recent study found that collisions may soon wipe out globally threatened creatures like maned wolves, brown hyenas, and leopards. We are, quite literally, driving some of the world’s rarest animals to extinction.
For more than half a century, countries have attempted to solve this problem using wildlife crossings. France constructed the world’s first crossings, known as passages à faune, in the 1950s, followed by Germany and the Netherlands. During the 1970s and ’80s, a handful of American states, including Wyoming, Florida, and New Jersey, built their own crossings. Many showed promise: After a 100-foot passage was installed beneath I-70 in Colorado, for instance, hundreds of mule deer trotted through each summer.
A new section of the German Autobahn 14 and a wildlife overpass between the Colbitz and Tangerhütte junctions.
Ronny Hartmann/Picture Alliance via Getty Images
Yet crossings were slow to catch on in the US, for several reasons. Few states rigorously collected data on animal collisions, masking the problem’s severity. Some early structures were poorly designed or monitored, casting doubt on their efficacy. And even when agencies did document successful crossings, tight budgets rarely had room for more. “The unfortunate thing to date is that the most effective solution is also the most expensive,” wrote one California official in 1980.
Over time, though, collisions became impossible to ignore. As human populations grew, traffic spiked in rural areas. Meanwhile, elk, bear, moose, and especially deer were bouncing back after centuries of exploitation. When speeding cars struck these hefty mammals, the crashes could be catastrophic for both parties. In 1995, researchers estimated that deer collisions caused 29,000 injuries and around 200 human deaths every year in the US. Animal crashes had become a public safety crisis.
In 2005, Congress ordered the Department of Transportation to study the situation. Its report, published three years later, put some firm figures on the issue. The authors tallied all the expenses of a crash — the hospital bills, the vehicle damage, the value of the animal itself, and so on — and found that the average deer strike dinged society more than $6,000. Moose and elk were even pricier. All told, animal crashes were estimated to cost America over $8 billion a year.
Against that backdrop, wildlife crossings were no longer viewed as frivolous expenditures, but vital public safety measures. In Wyoming, underpasses on Highway 30, paired with roadside fencing that guided animals toward them, cut mule deer collisions within a critical migration corridor by more than 80 percent, offsetting construction costs in just five years. In Arizona, underpasses and fences prevented enough elk crashes to do the same.
Prongorn antelope approach a wildlife overpass across route 191 at Trapper’s Point near Pinedale, Wyoming.
William Campbell/Corbis via Getty Images
New technology advanced the cause, too. Motion-activated cameras snapped high-quality photographs of animals moving through crossings, winning over skeptics, says Patricia Cramer, an ecologist who has studied crossings in Florida, Utah, and other states. “We could finally show the engineers that structures work,” she said. “Suddenly, they believed us.”
Money for animal infrastructure has been hard to come by — until now
As wildlife crossings proved their worth, transportation agencies took a new interest. Highway acts in 2012 and 2015 expressly allowed states to spend federal dollars on wildlife infrastructure. New overpasses and underpasses popped up, particularly in western states like Wyoming and Montana, where deer and elk followed predictable migration routes that highways happened to bisect. Their approval ratings soared, too: One poll found that more than 90 percent of voters in Nevada — hardly a state that habitually embraces government interventions — were in favor of more crossings.
But crossings remained underfunded. Wildlife projects drew from the same pots as basic transportation needs, like lane repaving and highway repairs. Pitted against America’s crumbling infrastructure, animals got short shrift. (This was especially true for small species that didn’t endanger drivers — it’s likely no one has ever totaled their truck by slipping on a salamander, for example.) In 2013, when researchers asked nearly 500 officials why crossings weren’t more common, two-thirds chalked it up to money.
In the face of chronic fiscal shortfalls, some states got creative. Colorado allocated lottery revenue. Wyoming sold specialty license plates. In California, where engineers will soon break ground on a massive bridge for mountain lions, the conservation group National Wildlife Federation solicited private donations. (Leonardo DiCaprio was an early contributor.) But these revenue streams were piecemeal and unreliable, and many otherwise worthy crossings never got built.
In 2013, road ecologists, led by ARC Solutions and a group called the Western Transportation Institute, began to discuss securing more permanent funds. Conservationists and scientists wrote policy papers, met with congressional aides, and hammered out the basic framework for wildlife-crossing legislation. As the proposal developed, it gained supporters. Animal welfare groups like the Humane Society backed crossings to reduce wildlife deaths and suffering. Conservation organizations like the Wildlands Network touted crossings as a way of stitching up fragmented ecosystems. Even pro-hunting organizations trumpeted the restoration of healthy deer and elk herds as a selling point.
“We use the lingo ‘win-win’ a lot, but in this case this was truly a win-win-win-win” —Susan Holmes
“We use the lingo ‘win-win’ a lot, but in this case this was truly a win-win-win-win,” said Susan Holmes, federal policy director for the Wildlands Network. “Almost everyone could see the value in this.”
With backing from hunters and highway safety advocates alike, animal-friendly infrastructure racked up unlikely congressional support. In a 2019 hearing on crossings, Sen. John Barrasso, a Republican from Wyoming and a former surgeon, said that he’s taken care of patients injured in collisions with wildlife. “It happens every year,” he said. Although Barrasso has a history of impeding climate-friendly initiatives — and a 7 percent lifetime score from the League of Conservation Voters — he included a wildlife crossing program in the highway bill that he sponsored later that year. (That version of the bill never passed.) Crossings also garnered support from Shelley Moore Capito, a Republican senator who chairs the chamber’s Environment and Public Works Committee — perhaps because Capito’s home state of West Virginia leads the country in deer crashes.
The years of lobbying paid off this month, when the $350 million wildlife-crossing provision made it into the final infrastructure bill — the largest federal public works program since President Dwight D. Eisenhower kick-started the interstate system in the 1950s. (Thirteen GOP House members and 19 senators voted for the bill; despite Barrasso’s affinity for crossings, he wasn’t one of them.) The funding will be disbursed through a five-year competitive grant program, through which states, Native tribes, and other entities will submit proposals for new crossings within their jurisdictions. Now animals will have a separate pool of money from which officials will be able to draw.
“This is finally approaching a scale that’s needed nationwide,” said Rob Ament, road ecology program manager at the Western Transportation Institute. “We can’t treat every mile of highway, but we can take care of a lot of the areas that are seriously affecting wildlife populations.”
The future of wildlife crossings is mobile
The new funding comes at a crucial moment. As the climate warms, it’s imperative that animals are able to move freely around landscapes. Think of moose shifting their ranges northward to escape infestations of hungry ticks, or bears fleeing wildfires intensified by drought. Crossing structures allow these creatures to navigate roads in search of novel habitat.
Then again, crossings only go so far: An elk migration corridor might drift northward over decades, but a bridge or tunnel can’t follow. At least, not yet — but that, too, may change.
According to the INVEST Act, the wildlife crossing program will prioritize structures that incorporate “innovative technologies” and “advanced design techniques.” Among those techniques, says Callahan, might be the use of fiber-reinforced polymer, or FRP, a plastic that’s lighter and stronger than regular concrete, and should soon be cheaper as well. The Western Transportation Institute and the California Department of Transportation are currently designing America’s first FRP wildlife bridge, and experts say that future iterations could someday be modular and mobile, capable of being disassembled and relocated in response to changing animal movement patterns. “That would be a game changer,” Callahan said.
Eastbound Interstate 90 traffic passes beneath a wildlife bridge under construction on Snoqualmie Pass, Washington.
As exciting as all that may be, it’s important to remember that the new funding for wildlife crossings is merely a good start. While $350 million may sound substantial, it is, as Cramer puts it, “decimal dust” compared to national transportation budgets. It’s also a fraction of what’s ultimately needed: According to one recent report, it would cost $175 million to deal with roadkill hot spots in California alone. What’s more, wildlife crossings can’t do much about traffic noise, salt pollution, stormwater runoff, or many of the other byproducts of roads — some of which will, ironically, be exacerbated by the infrastructure bill, which allots millions to highway expansion projects. And all the crossings in the world won’t help unless we get better at protecting the habitats that animals must move between.
“We can build a bridge,” said Matt Skroch, project director for public lands and rivers conservation at the Pew Charitable Trusts, “but let’s not build a bridge to nowhere.”
Correction, November 12, 10:40 am: A previous version of summary text for this story misstated the amount of INVEST in America Act funding that is related to wildlife crossings. It is $350 million.
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