Each day, thousands of animals face one of the most deadly predators in America — a road.
More than 4 million miles of public roads across the U.S. provide vital links for commerce, services, and travel, but they’re treacherous barriers for wildlife seeking food, water, and mates. Exposed and unsure about the noisy, unfamiliar terrain presented by an open road, an animal that hesitates or misjudges the speed of an approaching vehicle risks fatal consequences.
Unfortunately, those encounters are all too common on busy roadways. According to the Federal Highway Administration, there are more than 1 million wildlife-vehicle collisions (WVCs) every year in the U.S. In addition to the hundreds of thousands of animals killed and maimed, WVCs also result in hundreds of human fatalities and tens of thousands of injuries.
Collisions are expensive, too, costing more than $8 billion annually in vehicle repairs, medical costs, and carcass removal. The Western Transportation Institute at Montana State University gives sobering stats for the average cost of a single crash: $19,089 for a deer, $73,196 for an elk, $110,397 for a moose, and $82,646 for cattle and horses.
Roads can also disrupt migratory routes, divide up ecosystems, and inhibit intermingling, confining entire species to ever-shrinking habitats. A report by the U.S. Department of Transportation found that these crashes are among the biggest threats to the survival of 21 threatened or endangered animal species, from reptiles like the desert tortoise to mammals like the San Joaquin kit fox.
“It’s not just a direct killing that is a threat to the persistence of these species,” says Marcel Huijser, a senior research ecologist at the Western Transportation Institute. “It’s also habitat fragmentation and having smaller and isolated populations that may ultimately go extinct.”
Large Mammals like bears and deer can evade traffic by using overcrossings and undercrossings (here). (Credit: Colorado Department of Transportation, Colorado Parks and Wildlife, ECO-resolutions)
Comfort Zones
The word roadkill has been in the American vocabulary since the late 1940s, but it’s only been in the last several decades that studies have emerged examining the effect of roads on animals and the environment.
One solution that’s gaining traction is the wildlife crossing. Built over or under roadways, crossing structures allow animals to use custom-designed bridges and tunnels to get to the other side safely.
The first crossing structure in the U.S. designed for a specific species was a black bear underpass constructed in Florida in 1955. Twenty years later, the first overcrossing was built over Interstate 15 in Utah. Since then, some two dozen structures have been built or are being constructed in the U.S.
Crossing structures can be large, such as a bridge that spans a four-lane divided interstate highway, or small, like a culvert that channels water underneath a two-lane road and serves as a passageway for amphibians, reptiles, and small mammals. They’re designed to be comfort zones for various species, with soil, trees, and shrubs that mimic the surrounding terrain. Tall side walls and perimeter plantings on overcrossings help shield animals from the noise and sights of busy traffic below. For the most part, people are discouraged from using the structures, and signs posted at entrances warn off humans.
The results have been overwhelmingly positive for both animals and drivers. Data from a 2022 report by the Western Transportation Institute shows a whopping 83 percent reduction, on average, in the number of annual WVCs in areas where crossing structures exist.
The ongoing Snoqualmie Pass East Project in Washington has already seen the completion of multiple wildlife crossing structures along I-90. (Credit: Washington State Department of Transportation)
Safe Passage
Crossing structures to protect animals from the dangers of traffic were first constructed in France in the 1950s and can now be found around the globe. In Singapore, the Mandai Wildlife Bridge spans a busy highway and provides a vital link for the Central Catchment Nature Reserve, granting safe passage for endangered Sunda pangolins and other wildlife. Undercrossings encourage jaguars to move freely beneath the Nuevo Xcan-Playa del Carmen highway in the Mexican state of Quintana Roo. The Netherlands boasts more than 60 wildlife crossing structures within its modest borders.
In the U.S., construction of wildlife crossings has been gaining steam. Washington State has begun construction on the I-90 Snoqualmie Pass East Project, an ambitious $1 billion undertaking designed to improve roadways and enhance safety along a 15-mile section of I-90, a critical east-west transportation corridor. The project includes wildlife crossings over and under the interstate, helping to facilitate species connectivity in the rugged Cascade Mountains, and providing safe passage along the north-south migratory routes of deer and elk.
“We had some species using the crossing structures well before construction was even complete,” says Mark Norman, the biology and mitigation team lead for the Washington State Department of Transportation. “Deer and coyote would walk right by heavy construction equipment on their way through the incomplete structures.”
In 2016, Colorado finished building two wildlife overcrossings and five undercrossings on State Highway 9. A subsequent five-year study by the Colorado Department of Transportation (CDOT) and Colorado Parks and Wildlife (CPW) used 62 motion-activated cameras to record more than 110,000 successful mule deer crossings, plus crossings by elk, black bears, mountain lions, bobcats, and various small mammals.
“It was an extremely successful project,” says Michelle Cowardin, wildlife movement coordinator for CPW. “We saw somewhere around a 90 percent reduction in roadkill, and thousands of animals have successfully used that crossing structure. This project dramatically improved safety for motorists and wildlife.”
Those encouraging results prompted the formation of the Colorado Wildlife and Transportation Alliance, a collaborative administration with the specific goal of reducing WVCs in the state. The Alliance recently applied for — and in December of 2023 was awarded — a $22 million grant from the U.S. Department of Transportation to build a dedicated wildlife overpass across six lanes of I-25 south of Denver. That grant money comes courtesy of the Infrastructure Investment and Jobs Act of 2021, which authorized $350 million to improve wildlife connectivity and reduce wildlife-vehicle collisions.
When complete, the overcrossing will link 39,000 acres of prime big-game habitat on the east side of the interstate to the more than 1 million acres of the Pike National Forest on the west, helping ensure the health and vitality of one of the largest elk herds in the U.S.
“In my opinion, the federal Infrastructure Investment and Jobs Act is the best piece of transportation legislation since Eisenhower’s federal highway system act of 1956,” says Chuck Attardo, I-25 South Corridor Environmental Manager for the Colorado Department of Transportation.
(Credit: Tom Reichner/Shutterstock)
Conception and Creation
The process of building a wildlife crossing isn’t an easy one, and can take years of planning, data collection, and cost-benefit analyses. State departments of transportation compile annual statistics to document stretches of roads with high incidences of wildlife collisions. That info is combined with studies by biologists, federal and state agencies, and nonprofit environmental organizations to identify the numbers and species of local wildlife populations. Geological feasibility studies and negotiations with private landowners add layers of complexity.
“It’s important to realize that these projects can take a minimum of a decade to get them from conception through design and then construction,” says Cowardin. “You need a champion and strong partnerships for every one of these projects to follow them through to completion.”
In Oregon, planning has begun on the state’s first overcrossing to span Interstate 5 near the California border. The proposed $20 million overcrossing would provide a vital link within the Cascade-Siskiyou National Monument, one of the most biodiverse and ecologically complex regions in the U.S. Located at the confluence of the Cascade Range and the Siskiyou Mountains, the 114,000-acre space hosts over 600 plant species, and more than 300 species of birds, mammals, reptiles, and amphibians. It is a haven for butterflies, and several endemic fish are unique to the monument.
Crossings have drastically reduced wildlife deaths by traffic. (Credit: Melissa Kopka/istock via getty images)
Stepping Up
Fortunately, Oregon has its project champion. Amy Amrhein, a former congressional field representative for U.S. Senator Jeff Merkley, was inspired to act by years of hiking in the Cascade-Siskiyou National Monument and attending seminars on wildlife and connectivity issues. After retiring, she decided to devote the next phase of her life to advocating for a crossing structure in southern Oregon.
Not shy about making cold calls, in 2020 Amrhein reached out to Dave Willis, chair of the local Soda Mountain Wilderness Council. When Willis told her he’d been talking with local biologists and other supporters about the same idea, Amrhein knew she was onto something.
More phone calls and word-of-mouth contacts yielded a loose contingent of interested folks, including members of regional environmental organizations, the Oregon Hunters Association, the environmental group KS Wild, as well as 15 other nonprofits and state and federal agencies. State Representative Pam Marsh voiced support, as did Cidney Bowman, Wildlife Passage Coordinator for the Oregon Department of Transportation (ODOT).
“I fell off my chair and went, holy moly, nobody’s saying no,” says Amrhein.
Amrhein tapped into the collective energy by helping to organize tours in early 2021. A dozen or so people would crowd into Willis’ Ford Econoline passenger van and motor off to view possible crossing sites along I-5. Afterwards, they’d debrief at Amrhein’s house.
“We sat in my living room and said, ‘OK, how are we going to do this?’ ” recalls Amrhein. The first step was to organize. Deciding against the administrative complexities of nonprofit status, they dubbed themselves the Southern Oregon Wildlife Crossing Coalition (SOWCC). With Amrhein and retired wildlife biologist Jack Williams as co-chairs, the SOWCC outlined the next step: funding a feasibility study.
A nine-month grassroots fundraising effort by the SOWCC provided the $130,000 needed to contract completion of the Southern Oregon Wildlife Crossing Project Conceptual Design Report. The 114-page document detailed locations, construction methods, and projected costs for the proposed interstate overcrossing. Included was data from ODOT showing sections of Oregon roadways at high risk for WVCs. The data pointed directly at the area the Coalition targeted. The study helped greenlight ODOT’s design phase of the project and laid the groundwork for future grant applications.
Other community members have stepped up to help. When Karen Mager first heard about the SOWCC, she was all in.
“I’ve always been interested in research that relates to connectivity between wildlife populations,” says Mager, an associate professor of environmental science at Southern Oregon University. “It seemed like a really important applied project I might be able to contribute to.”
In the fall of 2021 Mager began working with undergrad students to set up 25 cameras along a 10-mile stretch of I-5 to monitor wildlife activity near the proposed overcrossing site. Over the next two years, those cameras captured more than 300,000 images and videos showing deer, elk, fishers, mountain lions, bobcats, and a variety of birds and small mammals — information essential for ODOT to begin designing a crossover structure appropriate to local animal populations.
“Getting into the mind of the deer and elk is what the challenge really is,” says Bob Grubbs, an ODOT engineer in charge of designing the proposed overcrossing. “What do they really like? What do they need to have to feel safe? We have to make sure they feel comfortable using a crossing bridge and that it does get used.”
A dose of bipartisan political willpower is helping move the Oregon project toward reality. Oregon House Bill 2834 authorized the Oregon Department of Fish and Wildlife to create the Wildlife Corridor Action Plan “to guide the preservation of long-term habitat connectivity for a broad diversity of wildlife species.” Meanwhile, the SOWCC and other stakeholders continue to pursue federal funding and hope for construction on the crossing to start possibly by 2026 or 2027.
“Caring about nature and wildlife and how we interact with it is essential to all people,” says Marcel Huijser. “These projects are a huge opportunity to reach consensus that’s independent of political orientation. That should be important to us as humans.”
This story was originally published in our July August 2024 issue. Click here to subscribe to read more stories like this one.
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