Happy Nice Mall

But Banff’s wildlife passes, like most, suffer from some sort of problem. Horseless Carriage Syndrome, their design is limited by the existing infrastructure. Tunnels are usually poorly adapted culverts, pipes (usually concrete) that carry water under roads. Overpasses are often borrowed wholesale from the highways and built as if to support the weight of an 18-wheeler, and then “overdressed” with greenery, Lister says.

ANDREW MERRITT

A series of experiments are starting to rethink this model. One is the Wallis Annenberg Wildlife Crossing, a $90 million wildlife bridge under construction north of Los Angeles. Designed by architect Robert Rock, this structure avoids the humpbacked arch of old bridges, a vast flat expanse that only needs one pillar to support it between mountains and along a highway that an estimated 300,000 cars pass each day. It’s “the poster child for innovation,” says Renee Callahan, executive director of ARC Solutions, a group that explores how to build better wildlife bridges. “It was literally designed for species from mountain lions to mule deer to deer mouse,” Callahan says. “They’re designing literally everything from soil terms to the mycorrhizal layer to make sure the soil itself has a cork network that can support natural vegetation.”

There are many unknowns when construction begins, not least how different types will react to the volume of vehicles passing under them. The National Park Service will monitor activity on the bridge as well as DNA profiles of animals on both sides of the highway. Many are watching to see what happens to the mountain lion population in the area. Over time, inbreeding led to genetic abnormalities, such as a distinctive bend in the tails of domestic cats. The agency predicted that the population would become extinct within decades without a transition.

Across the US, $350 million of the infrastructure bill falls far short of what is needed to address the fragmentation created by the nation’s 4 million miles of public roads. But there are a handful of innovations that could drive cost-benefit analysis by allowing transitions to be built at lower cost or where it was not possible before.

Animal bridges are currently only built where there is protected land on either side of the road, as it would be difficult to justify the typical expense of building a concrete bridge in an area that someone could develop in a few years. Lighter, cheaper, modular systems can be used where their future is less secure, explains Huijser: “If the adjacent land isn’t suitable for wildlife, we’ll tear it apart and you can move it.”

A candidate material for such modular systems is precast concrete. There is also excitement fiber reinforced polymer (FRP)a less dense material than concrete, made of structural fibers embedded in resin. FRP has been used to build pedestrian and bicycle bridges in Europe and a quick and easy wildlife bridge in Rhenen, just south of Gooi in the Netherlands. Currently, the Federal Highway Administration does not allow it to be used in traffic infrastructure in the United States, but there are increasing demands for replacement. “These are mainly policy and governance barriers. They’re not about science or technology,” says Lister.

“They know the last thing anyone would want is to build a large structure with a lot of publicity – and then it just doesn’t work.”

Darryl Jones

Designers like Lister and innovators like Callahan are vocal advocates of building wildlife bridges across the country. Road ecologists and wildlife scientists are more cautious. “They’re overly critical because they know the last thing anyone would want is to build a big structure with a lot of publicity and then it won’t work. Because everyone will come out of the woodwork and say, ‘Look! A waste of time! It’s bullshit!” says Jones.

However, today even cautious types want to see more structured. While we haven’t done enough research to get all the answers, Huijser says it would be dangerous to take this as a sign that we should stop. Such extreme prudencetype II error”—a false negative. At this time of mass extinction, it’s like the house is on fire, and our solution so far has been to fire a water gun on it a few times. It would be a mistake to conclude that water is not the answer.

Despite challenges in Ede and elsewhere, Van der Grift says the answer is to learn as you build. He emphasizes that we still need to invest in real studies such as tagging, installing trace cameras, and DNA testing and long-term population monitoring. But first we must build more gateways – and the evidence we have so far tells us to build big and bold. “You have to realize that you can hardly do much,” he says. “Do what you think is necessary, study, and then nine out of 10 times you’ll see, ‘Oh, I should have done more.’ But there’s no point in waiting until you realize that.”

Matthew Ponsford is a freelance reporter based in London..