Almost seamlessly, the two sides of a scenic forest in Alberta, Canada, have been woven back together.
Located between Calgary and Banff National Park, this stretch of the Canadian Rockies is sliced in two by the Trans-Canada Highway, one of the busiest roadways in the province. That’s had deadly consequences for the area’s abundant wildlife, as well as the tens of thousands of people who drive through it every day. But now, after years of mounting wildlife-vehicle collisions, the danger to animals and humans is being addressed with a stunning new wildlife overpass.
The Bow Valley Gap wildlife overpass is a roughly 200-foot-wide cap over a four-lane highway, topped with soil and forest-like plantings that creates a bridge almost indistinguishable from the forest on either side.
The design and engineering firm Dialog led the structural engineering and landscape architecture of the overpass, which was funded by Alberta’s provincial department of transportation and is now the first wildlife overpass in Canada constructed outside of a national park. It’s in an area where reported vehicle collisions with deer, elk, coyotes, and grizzly bears happen 69 times per year on average. “The very rough rule of thumb is for every collision that is recorded or every carcass that is seen on the side of the road, you can usually double that number,” says Dialog’s Neil Robson, the overpass project manager and lead designer.
“The best way to mitigate collisions is to try to prevent them. The number one way to prevent them is actually fencing. But fencing doesn’t allow connectivity of the animal. It keeps them on both sides of the highway,” Robson says. “Very helpful for collisions, but not helpful for migration patterns, connectivity, the ability to get mates, genetic diversity, and that’s where the overpass comes into play.”
The overpass sits atop two arched tunnels that cover the two traffic lanes and shoulders on each side of the road. Seen from a driver’s perspective, the overpass has a smooth M shape, and is covered with grasses, shrubs, and trees. A tall metal fence runs along its edges, as well as on the sides of the road leading up to the overpass, running a total of more than seven miles.
Robson says the design of the overpass was heavily informed by animal migration data, with its width sized to accommodate the large species that are known to travel in this area. Wildlife biologists were involved during the initial design phases for the overpass and helped to shape its look and form. The overpass topography was influenced by the species that live in the area, and its slopes were calculated to accommodate what animals—both predator and prey—need to see to survive in the wild.
“If you’re going up a crest and or up a hill and it’s too sharp, that’s not ideal for a prey species because they don’t really have the line of sight [to avoid predators],” Robson says. “Flatter topography for viewpoints and not having blind corners and other types of things also factor into the design.”
These kinds of considerations are fairly new ones for wildlife overpasses. Dialog has some experience in this unique building typology, having designed a handful that already exist in Banff National Park. But Robson says the design process has become much more interdisciplinary in just the past few years, with designers and scientists working together. “It’s not just the engineering professional inheriting the recommendations from the biologist and ecologist or reading the report and then making their own decisions. We’re going to those sites together. We’re working through the designs together,” he says.
That’s even affecting how these projects are planted. For the Bow Valley Gap overpass, scientists helped determine the ideal mix of plant species that would mimic the forest surroundings but not encourage animals to linger near what is still a potential collision area.
“We do want the landscape architecture on top, the grasses, the shrubs, and the trees, to be as close to the natural surroundings as possible,” Robson says. “But you also don’t want them to be overly edible, because if you plant them in and a herd of deer or elk start to chew on things, you’re not going to have much vegetation left.”
Those plants are still maturing on the overpass, which was officially completed in December. But even as it grows in, Robson says the design process behind the overpass is informing future wildlife overpasses in Canada, including three that Dialog is currently designing. And, perhaps more importantly, it’s already being used by the species it was designed to protect.