Helping Wildlife Cross I-40 in the Pigeon River Gorge

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As the world warms, wildlife populations need to expand northward. Highways are formidable barriers to this movement. A project along I-40 near the Smokies hopes to install crossing structures to protect wildlife and people.

It’s not unusual for traffic to slow to a crawl at rush hour along a stretch of Interstate 40 that snakes through the Pigeon River Gorge between Asheville, North Carolina, and Knoxville, Tennessee. But on this summer day, cars, trucks and everything in between grind to a halt in both directions as a mother black bear suddenly enters the roadway leading two small cubs out into heavy traffic.

Drivers slam on the brakes, and passengers lurch forward, mouths agape in amazement. In a quintessential “right place, right time” occurrence, Susan Detwiler has a front-row seat in her vehicle next to her husband, Kevin Detwiler. She grabs her cellphone and captures a video of the bears’ safe passage across two lanes of westbound traffic, over the high Jersey barrier in the middle, and then across the two eastbound lanes, finally disappearing into the brush on the other side of the road.

But wait! There’s a third cub, lagging behind the others and having trouble scaling the barrier. “C’mon baby,” coos Detwiler as the little bear finally topples over the slick concrete divider and lopes to safety not far from the Appalachian Trail and the boundary of Great Smoky Mountains National Park.

 “Unfortunately, that viral 17-second clip Susan Detwiler captured on August 19, 2018, shows the antithesis of what normally happens,” says Jeff Hunter, senior program manager for National Parks Conservation Association (NPCA). “The fact that traffic miraculously stopped for these bears was such an anomaly that the footage became the poster child for our project, demonstrating the need for wildlife-crossing structures in this perilous section of highway.”

Hunter is the facilitator for Safe Passage: The Pigeon River Gorge Wildlife Crossing Project, an effort spawned in 2017 by nearly 20 federal, state, tribal and non-governmental organizations. More than 100 individuals are now collaborating to make this 28-mile stretch of I-40 in western North Carolina and east Tennessee more permeable for wildlife and safer for people.

Why animals cross the road

More than 12.5 million people come to Great Smoky Mountains National Park annually—and many more visit the region—largely drawn by the desire to see black bear, elk and other wildlife. But the Smokies’ iconic species don’t recognize the park boundary. Just like us, they travel around in search of shelter, food and mates.

“A recent study determined that more than 90% of male black bears and 50% of female black bears regularly travel out of Great Smoky Mountains National Park to access other habitats,” says Bill Stiver, supervisory biologist for the park. “This inevitably means they have to cross regional highways as well as secondary roads.”

I-40 was created in the 1960s. Like hundreds of roads that now crisscross the Southeast, it sliced through a mountain landscape where for millennia animals had freely followed ancient trails called wildlife corridors. Now 27,000 vehicles travel through the Pigeon River Gorge every day and wildlife mortality from collisions here is rapidly rising. Some years have seen as many as 70 road-killed bears in this 28-mile section of highway alone—and bear populations here have quadrupled in the last four decades.

What’s more, reintroduced elk are also moving out of the park and attempting to cross these roads, joining their fellow ungulates, the prolific white-tailed deer, in sad deaths often involving hours of suffering. There is no way to count the many individual animals who sustain severe injuries and make it off the roadway only to die later in the forest. With both animal and human populations increasing alongside growing travel in the region, this situation is only expected to get worse over the next decade.

“Human infrastructure is making it increasingly difficult for wildlife to follow their natural patterns of movement across the landscape,” says Hugh Irwin, a landscape conservation planner with The Wilderness Society. “New infrastructure needs to take wildlife movement requirements into account, and existing infrastructure needs to be retrofitted over time to enable wildlife movement.”

To complicate matters even further, scientists expect climate-driven species will soon be migrating through southeastern North America and into the Appalachians. Many believe it’s time for changes to roads here, especially so that the region’s iconic species can use existing wildlife corridors to migrate north.

Ron Sutherland works to re-establish wildlife corridors throughout the eastern United States as chief scientist with Wildlands Network. He defines habitat connectivity as “the degree to which organisms are able to move freely across the landscape. A wildlife corridor is the term we use for a defined movement pathway that—if protected or restored—would provide essential habitat connectivity for one or more species,” he says. “Naturally one of the best places to put wildlife crossings is where you have a wildlife corridor that gets cut off by a highway.”

How to help them cross

For years, road ecologists around the world have been working to make roads safer for both animals and humans. Europe, Canada, Mexico and many U.S. states have already created effective wildlife crossings. Recent articles and videos featuring crossing structures in Utah and Texas have been shared widely on social media.

Other regions have successfully solved road ecology problems by improving existing structures like culverts that wildlife use to cross, constructing mammal underpasses, and building large, expensive vegetated wildlife overpasses, which, when paired with fencing, have been shown to successfully reduce collisions.

In the steep vertical terrain of the Pigeon River Gorge, the best solution is not as easy to come by as in the open landscapes of the west. Safe Passage has focused for two years on collecting data that will prepare the group to collaborate with partners in local departments of transportation on bridge improvements planned for the next five years.

The first of these bridge repairs may begin as early as fall of 2021 at the Harmon Den exit near the intersection with the Appalachian Trail. Living on both sides of I-40, a herd of elk now call this area home after dispersing from a population reintroduced in the Smokies 20 years ago.

“The topography is driving where these elk are moving,” says Dr. Liz Hilliard, a wildlife biologist with Wildlands Network who is using GPS collars to research species movement and mortality in the Pigeon River Gorge. “They’re trying to spend the least amount of energy, so they follow low-slope areas, moving through the landscape in what we call the path of least resistance.”

It is important to locate wildlife crossings where animals wish to cross the road, not just where it may be easy or convenient from a construction perspective. Scientists and researchers can help road planners know where animals try to cross by studying wildlife mortality, collision data, migration routes and the geographical terrain of the area.

While some animals take years to become comfortable using crossing structures, others can adapt to them rather quickly. Fencing is often used to keep wildlife off the highway and funnel them to safe crossing opportunities, saving individual lives and helping populations thrive.

“The solution to addressing issues of wildlife and highway interaction is two-pronged: fencing plus crossing structures,” says Terry McGuire, a road ecology expert and highway engineer now retired from Parks Canada. “It has been shown through research that one does not work as effectively without the other.”

McGuire also points out that one type of crossing does not necessarily meet every animal’s needs and, ideally, a combination of various crossing types—like a buffet of choices—should be provided, spaced out in such a way that animals do not need to travel great distances to find a crossing opportunity.

While the concrete Jersey barriers prevent many individual crossings, scientists are concerned about an even bigger issue called the “barrier effect.” When a species finally stops trying to cross the road at all, the highway has become a barrier and the species may be at risk of extirpation.

“This is because the habitat is now fragmented,” says Hunter, “preventing the healthy genetic exchange that species need to thrive.”

One step at a time

“Human roads have negatively affected where wild animals live,” says Kim Delozier of Appalachian Bear Rescue, a facility that takes in orphan cubs just outside of Great Smoky Mountains National Park in Townsend, Tennessee. “It is our responsibility to do our best to minimize these impacts and help these wild creatures travel safely where they live. The need for wildlife crossings warrants the effort and money necessary to make it happen.”

It’s been nearly four years since Detwiler captured the bear crossing video. In that time, the Jersey barrier that divides I-40 has been increased in height by several feet.

“Our research in the Pigeon River Gorge is now in its final stages, and we don’t have all the answers yet,” says NPCA’s Hunter. “But one thing we do know is that collaborative partnerships like Safe Passage are critical to finding the best path forward.”

Visit smokiessafepassage.org to see the Susan Detwiler video, learn more about the project, or make a donation to fund wildlife-crossing structures and fencing in the Pigeon River Gorge. 

Help for the Smaller Creatures

Bobcats, coyotes, foxes, raccoons and other medium-sized species already use several existing culverts under Interstate 40, like the one shown here. Large and small creatures alike traverse the Pigeon River Gorge landscape via a double tunnel where engineers left habit connected on top and inadvertently created a land bridge. Safe Passage researchers are examining “hotspots” where the most animals are getting killed, as well as where some are successfully crossing the interstate—helping them learn more about possibilities for mitigation options.

The story above appears in our March/April 2021 issue. For more like it subscribe today or log in with your active BRC+ Membership. Thank you for your support!