How wildlife crossings in Canada are inspiring safer roads for global species

  • The stretch of Trans-Canada highway that runs through Banff National Park was once incredibly dangerous for animals and motorists alike, but today the park has more wildlife crossing structures than anywhere else in the world and the data to support their effectiveness.
  • The crossing structures at Banff inspired a project on I-90 in the U.S. state of Washington with its own location-specific twists.
  • Tribal efforts also led to a Banff-informed development project on US-93 in the Flathead Indian Reservation in Montana that respects local people and wildlife.
  • Lessons from Banff are informing projects beyond North America: In Costa Rica, emerging crossing structure projects protect jaguars and canopy-dwelling creatures.

There once was a stretch of Trans-Canada highway so perilous it was known as “The Meat Maker.” The then-infamous section of road that transects Banff National Park, a breathtaking expanse of mountainous terrain and glacial lakes in the Canadian Rockies, averaged about 100 elk-vehicle collisions each year.

In the early 1980s, a simple highway expansion project widened the busy road from two lanes to four, with the added objective of cleaning up Banff’s roadkill problem by enabling animals to cross safely. There was little indication that, within decades, Canada’s oldest national park would boast the most wildlife crossing structures anywhere in the world, including 38 underpasses (tunnels) and six overpasses (bridges) as of 2014. It was perhaps even less obvious that this project would generate a wildlife monitoring program bound to shake up global road ecology paradigms.

“The focus at the beginning wasn’t about large carnivores or connectivity conservation,” said Tony Clevenger, a senior wildlife research scientist at the Western Transportation Institute at Montana State University in the U.S. “It was about protecting the motorists.”

By the mid- to late-1980s, the park’s first dozen underpasses had been completed. These were followed by more underpasses by the mid-1990s, as well as two overpasses (each about 50 meters, or 164 feet, wide) due to growing concern for wolves and grizzly bears.

“That’s where I came in,” Clevenger said. “They had built those first dozen underpasses, but those weren’t really monitored very much. The park needed good science-based information to guide the design, planning and siting of the last phase.”

Crossing structures themselves are not a novel concept. The first wildlife bridge was built in France in the 1950s (not for conservation purposes, but to help hunters guide deer), followed by the construction of more crossings around Europe. However, these structures were not typically monitored. There wasn’t much data on how well the wildlife crossings worked or what species were using them.

A road going through Banff National Park in Alberta, Canada. Image by Mallya8 via Wikimedia Commons (CC BY-SA 4.0).

When he arrived in Alberta, Clevenger began a four-year contract with Parks Canada to gather much-needed data for the final phase of Banff’s crossing structure construction.

The insights Clevenger and his colleagues gleaned in their first years of research informed the construction of four overpasses and about 17 underpasses. But when his contract ended, Clevenger realized he wasn’t ready to leave Banff behind. So he formed a partnership with conservation organizations to continue his research and shifted his focus to the crossings’ conservation-level benefits.

“After the first five years, I realized this was a unique place in the world to be doing this sort of research,” Clevenger said. “It was leading edge. Nobody was doing it anywhere, and nobody had this sort of lab for doing this sort of research — especially a national park where you’ve got all this wildlife research happening at the same time, which we could tap into.”

By this time, Clevenger and colleagues had already published a study demonstrating that wildlife crossing structures effectively reduced vehicle collisions with deer by about 86%. To explore whether the crossings also benefited entire animal populations, not just lucky individuals who might otherwise wind up as roadkill, Mike Sawaya, who was then finishing a doctorate at Montana State University, worked with his adviser, Steven Kalinowski, and Clevenger to develop a simple technique for snagging hair from black bears and grizzlies when they used the structures.

Through DNA analysis, the researchers could determine the species, sex and individual identity of each animal that shed as it crossed. Ultimately, the research provided evidence, for the first time, that the crossing structures enabled otherwise isolated bear populations on either side of the highway to breed. Animals weren’t just using the crossings — they were relying on them to prevent genetic isolation.

“In the first two or three years of the work, I still don’t quite understand it, but there was just a lot of skepticism from biologists who believed that wildlife crossing structures weren’t effective, even though they had no data to prove it and hadn’t done any monitoring,” Clevenger said. “Some of these biologists said the only way to effectively save the highway was to raise it 45 miles [72 kilometers] through the park, which of course is impossible. But our data showed the wildlife crossing measures were highly effective.”

“And it wasn’t just the data we that we shared,” Clevenger added. “It was also just the fact that the overpasses were built. At that time, this was a compelling argument to people in the Department of Transportation that these structures worked. They weren’t just a dreamlike, conceptual thing. They were concrete.”

An overpass over a highway in Banff National Park. Image by AP Clevenger, courtesy of ARC.Solutions.

Part of their home range

South of Banff, in the U.S. state of Washington, Department of Transportation engineers and other state and federal agencies began discussing plans for a project to expand a 24-km (15-mi) stretch of another transcontinental freeway in the 1990s. With traffic volume increasing on I-90, reflective jersey barriers were being placed between eastbound and westbound lanes to keep drivers safe at night — a workaround that was creating an added impediment for wildlife.

“The National Forest Management Act says we need to protect the viability of species,” said Patty Garvey-Darda, a Forest Service biologist who began working on the project in 1999. “It was pretty clear that I-90 was a barrier, risking the demographic isolation of the South Cascades.”

To investigate how best to implement their own crossing structures in Washington, Garvey-Darda and some of her engineer collaborators traveled to Banff to see its overpasses and underpasses for themselves.

“Banff has been tremendous because they’ve done a really good job of researching and showing that these structures are successful,” Garvey-Darda said. “That is a lot of the reason we monitor.”

Construction of crossing structures on I-90 began after the project proposal completed the National Environmental Policy Act (NEPA) review process in 2008, with underpasses and one overpass constructed in more than half of the area to date and plans for additional large structures in the future. While the I-90 project has taken inspiration from Banff, the team has made numerous design tweaks to fit the local environment, including growing local vegetation in its underpasses.

“Usually you don’t try to vegetate your undercrossings,” Garvey-Darda said. “Sometimes that totally makes sense — it depends on which species you are trying to connect. But in our case, this is an old-growth forest ecosystem where you have a large number of low-mobility species, such as terrestrial mollusks and salamanders that are not associated with water. They don’t move very far. And we have a whole bunch of these tiny shrew species. Thinking that they’re going to go under something that’s unvegetated and be able to restore that genetic connectivity between populations is unlikely.”

Jaguar female crossing safely under a four-lane road at a drainage Costa Rica. Image courtesy of VAVS.

In hopes of incorporating the crossings ever more seamlessly with their surroundings, Garvey-Darda and colleagues are also entertaining the idea of inoculating the structures’ overlying soil with rare native fungi from the earth around I-90.

After decades of preparation, Garvey-Darda is enjoying the end result of the multi-agency collaboration. This year, she and her team spied a black bear using the crossings for the first time. And she notes that the structures have become just another part of the local habitat for deer and elk, which are often spotted lounging on the crossings, munching on native plants and nursing their young.

“I really never envisioned that deer and elk would just adjust and use the crossing structures as part of their home range,” Garvey-Darda said. “It’s pretty beyond cool for me.”

However, the I-90 wildlife crossings are not without their challenges — namely, people. Although Garvey-Darda has implemented an area closure for about 300 m (1,000 ft) on either side of I-90 to discourage curious humans from wandering onto the animal-only crossings, people are still tempted to take a look. If not managed carefully, this can create an entirely new problem.

“If people are in the crossing structures, then animals are more likely to get on the interstate,” she said. “Since the whole highway is fenced [to funnel animals toward the crossings], now you can have a herd of elk that’s all trapped within the fence — and now the safety hazard is so much worse.”

Clevenger and colleagues published a study demonstrating that wildlife crossing structures effectively reduced vehicle collisions with deer by about 86%. Image courtesy of CSKT, MDT, & WTI-MSU.

The road is a visitor

As with Banff’s Trans-Canada highway and Washington’s I-90 before their transformations, crashes were once common on the stretch of US-93 that crosses through the Flathead Indian Reservation in Montana. But in the early 1990s, when the Montana Department of Transportation (MDOT) began planning to widen the highway, a unique set of challenges arose. Namely, MDOT wanted a divided four-lane highway to accommodate increasing traffic and safety concerns.

But while the Confederated Salish and Kootenai Tribes (CSKT) who live on the reservation also wanted to improve the highway’s safety, they worried that the project would threaten the local ecology and destroy their community’s small-town feel.

“People would drive too fast, more people would move here, and it would become a bedroom community for the larger towns to the north and south of us,” said Whisper Camel-Means, a wildlife biologist who works for the CSKT Wildlife Management Program. “That could drive up housing costs and make it so tribal members could not afford housing on their own reservation.”

The project could not proceed without the tribes’ permission. With neither MDOT nor the tribes willing to budge, the governments remained locked in a stalemate for a decade.

“The meetings were contentious,” Camel-Means said. “People did not see eye to eye. It took progressive people in the Federal Highway Administration and Montana Dept of Transportation to accept that the tribes had the power to control political decisions on the reservation. We did not relent — we were strong and held our ground.”

Eventually, the tribes’ efforts paid off. The state, federal and tribal governments agreed to proceed according to the principle that the road is a visitor: any highway developments must respect the needs of the local people and wildlife. In the years that followed, the parties held design meetings to discuss plans for each section of road, ultimately resulting in a highway that oscillates between two lanes and four and contains one wildlife overpass and 38 underpasses.

As with the I-90 project, decision-makers toured Banff’s structures in the early phases, adapting the national park’s concepts to suit the medley of towns, rural residential areas, businesses and protected wildlife areas that constitute US-93. Marcel Huijser a research ecologist with the Western Transportation Institute at Montana State University, identified a challenge inherent in such varied landscapes: coping with shorter sections of fence to guide animals to the crossings.

An underpass through a highway in Banff National Park. Image courtesy of AP Clevenger, courtesy of ARC Solutions.

“We have access points — far more than we would have in a national park,” Huijser said. “And what we found is that if you have road length that is fenced for less than 3 miles [5 km] or so, you are no longer reliably reducing collisions with large mammals by 80% to 100%. We have to be careful, especially with multifunctional landscapes where there’s pressure to implement fences over a shorter length, that we don’t make them too short.”

Still, Huijser says there’s much to celebrate in the environmentally conscious project that grew out of the tribes’ perseverance.

Crossing structures that promote connectivity for terrestrial wildlife “only happened because of the legal position of the tribes,” Huijser said. “That is the fundamental thing that should not be forgotten about the Highway 93 project, because we all know what the original plans looked like: four lanes, a turning lane in between, and a narrow culvert for a stream crossing.”

Big cats and biodiversity

Tropical countries also face a need for safer, more sustainable roadways. But while many animals die each day on the highways of Costa Rica, collisions with small anteaters fail to generate the public outcry triggered by collisions with massive elk.

“For us, it’s a little bit difficult because right now in Costa Rica they don’t see this as a human problem,” said Daniela Araya-Gamboa, creator and coordinator of the Wild Cats Friendly Roads Project through Panthera. “People don’t see the small animals dying on the road. In one of our projects we are working with here, we expect 4,000 dead wild animals on the road per year. It’s crazy, and it’s real, and nobody knows about it.”

When Araya-Gamboa started working for Panthera in 2011, her project collected data on a gravel road that was about to be paved, threatening jaguar connectivity. Around this time, she met Clevenger at a workshop in Mexico and the researchers began exchanging ideas.

“I went to Banff because that was my dream,” Araya-Gamboa said. “I wanted to be there and to see how the underpasses are working. Thanks to Tony and the work they have done there, most of the world can see [Banff] as a model that we can adjust for our countries.”

A mountain lion exiting an underpass. Image courtesy of CSKT, MDT, & WTI-MSU.

“What we’ve learned [in Banff] has been used throughout the world,” Clevenger said. “In Asia, Latin America and Africa, there’s a tsunami in terms of the transportation infrastructure that is being built. This is causing huge, huge impacts on some of the richest areas in the world in terms of biodiversity. What we’ve learned in North America probably isn’t applicable in some situations, but certainly the general principles are.”

Today, the Wild Cats Friendly Roads Project supports Costa Rica’s Ministry of Public Works and Transport and Ministry of Environment, Energy and Telecommunications, including through the collaborative development of a guide designed to help the government implement sustainable road measures for wildlife.

Through Araya-Gamboa’s research and the work of other scientists, the project has also identified how road projects can specifically protect jaguars, which are sometimes killed crossing roads in the touristic part of the country.

When Araya-Gamboa and colleagues found a young female jaguar lying dead on a recently built four-lane road, they set out to discover whether they could invite her mother, sure to be lingering nearby, to cross safely using a big, dry square culvert. Using camera traps and a spritz of standard jaguar lure (the cologne Obsession by Calvin Klein), the team snapped a picture of the female crossing via the structure.

“We used that information to recommend sizes and designs for measures on four roads that are being built or expanded in [parts of] Costa Rica where we have jaguars,” Araya-Gamboa said.

In addition to guiding jaguars across expanding highways, Araya-Gamboa and colleagues have set their sights on securing safe crossings for canopy dwellers such as monkeys, opossums and squirrels to preserve biodiversity in the highest reaches of the forest. To do this, they use arboreal crossings: cheap, simple rope bridges that stretch between separated canopies. But while arboreal crossings can help, some animals, including spider monkeys, refuse to use them.

The Wild Cats Friendly Roads Project has set its sights on securing safe crossings for canopy dwellers such as monkeys, opossums and squirrels to preserve biodiversity in the highest reaches of the forest. Image courtesy of Panthera.

“We have made clear that you have to avoid cutting the canopy,” Araya-Gamboa said. “That’s the golden rule. If you have natural tree connectivity over the road, you have to protect it, because it will be difficult to replace that natural connectivity with an arboreal crossing.”

For regions that want to implement crossing structure projects for the first time, Araya-Gamboa offers advice that holds true regardless of climate or ecological makeup: collect data.

“If you don’t have data, you have nothing,” she said. “Collect data, make people aware of what is happening, and then use that moment to start improving legislation for implementation of measures.”

Banner image: A black bear entering an underpass. Image courtesy of CSKT, MDT, & WTI-MSU.


Clevenger, A. P., Chruszcz, B., & Gunson, K. E. (2001). Highway mitigation fencing reduces wildlife-vehicle collisions. Wildlife Society Bulletin, 29(2), 646-653. Retrieved from

Sawaya, M. A., Kalinowski, S. T., & Clevenger, A. P. (2014). Genetic connectivity for two bear species at wildlife crossing structures in Banff National Park. Proceedings of the Royal Society B: Biological Sciences, 281(1780), 20131705. doi:10.1098/rspb.2013.1705