Within the experimental world of animal infrastructure

But Banff’s wildlife crossings, like most, suffer from a sort of horse-drawn carriage syndrome, depending on the infrastructure in which their designs are located. Tunnels are often poorly adapted holes, pipes that pass water under roads (usually concrete). And in general, wholesale crossings from the roads have been borrowed: they are built as if they were carrying the weight of an 18-wheel drive, and then covered with leaves, Lister says.


A scattered experiment has begun to rethink this model. One is the Wallis Annenberg Wildlife Crossing, a $ 90 million wildlife bridge under construction in northern Los Angeles. Designed by architect Robert Rock, it avoids the concave arch of old bridges, which requires a single column between the mountains and to support a highway that crosses 300,000 cars every day. He is the “child of the innovation poster,” says Renee Callahan, executive director of ARC Solutions, a team that researches how to build better wildlife bridges. “It’s literally designed for species that include mountain lions and mule deer and deer mice,” says Callahan. “They’re designing the bottom, literally, to the mycorrhizal layer, in terms of soil, to ensure that the soil has a network of fungi that can support its vegetation.”

There are many unknowns as construction begins, especially how different species will react to the large volume of vehicles passing below. The National Park Service will monitor the activity of the bridge, as well as the DNA profiles of the animals on both sides of the highway. There are many who are looking at what will happen to the mountain lion population. Over time, inbreeding has caused genetic abnormalities, such as an indicative kink in the tails of local cats. The agency predicted that the population would disappear over the decades without crossing over.

In the U.S., the $ 350 million infrastructure bill is far from the amount needed to deal with the 4 million miles of public roads in the country. But there are some innovations that can be used to build cost-effective crossings at lower cost or in places that were not previously viable.

Animal bridges are only built where there is protected ground on both sides of the road, as the typical cost of building a concrete bridge would be difficult to justify in a site that someone could develop in a few years. Lighter, cheaper and modular systems could be used in places where the future is less secure, Huijser explained: “If the adjacent land becomes unsuitable for wildlife, we dismantle it and you can move it.”

One of the preferred materials for these modular systems is precast concrete. There is also the excitement of fiber-reinforced polymer (FRP), a material with a lower density than concrete, made of structural fibers laid in resin. FRP has been used to build bridges on foot and by bike in Europe and to build a quick and easy wildlife bridge in Rhenen, south of the Dutch Gooi. Currently, the Federal Highway Administration does not support the use of traffic infrastructure in the U.S., but there is a growing demand for change. “They are mainly barriers to politics and governance. They are not about science or technology, ”says Lister.

“They know that the last thing anyone wants is to build a big structure, with a lot of publicity, and then it doesn’t work.”

Darryl Jones

Designers like Lister and innovators like Callahan are advocating for the construction of wildlife bridges across the country. Road ecologists and wildlife scientists, on the other hand, remain more cautious. “They’re hypercritical, because they know that the last thing anyone wants is to build a big structure with a lot of publicity — and then it doesn’t work. They will all come out of the wood and say, ‘Look! Waste of time! It’s crazy! ‘Says Jones.

But today the prudent kind also wants to build more. Although we haven’t done enough research to get all the answers, it would be dangerous to take that as a sign that we need to stop, says Huijser. He calls excessive caution a “type II error,” a false negative. At this time of mass extinction, it is as if the house is on fire and our solution so far has been to throw a water gun several times. It would be a mistake to conclude that water is not the answer.


Van der Grift says that despite the challenges in Eden and elsewhere, the answer is to learn while building. We still need to invest in real-life labeling, roadblock installation, and DNA testing and long-term population tracking, he emphasizes. But we need to build more passages first, and the evidence we have so far says to build big and bold. “You have to realize that you can hardly do too much,” he says. “You do what you think is right, look at it, and then at nine out of 10, you’ll see, ‘Oh, I should do more.’ But it’s not worth waiting for that to happen. ‘

Matthew Ponsford is a freelance journalist living in London.


Leave a Comment