Huijser says the United States has been less inclined than its native Netherlands — and “almost anywhere else where I’ve worked” – to think of conservation as the goal of crossings. But that is changing. The Infrastructure Employment and Investment Act, signed in November and earmarked $ 350 million for wildlife crossings over the next five years, provides new federal funding for projects and research to reduce collisions. between wildlife vehicles and connecting fragmented areas. of habitat. While that amount is only 0.3% of the $ 110 billion budget for the road bill, road environmentalists have hailed it as a historic investment. There is now a publicly funded way of building conservation-oriented crossings, although collision reduction remains the main goal, says Rob Ament, a senior conservationist at the Center for the Conservation of the Great Landscape. Dedicated funding also means that wildlife crossovers no longer compete with potholes for scarce tax money. “I think it’s actually a big step forward,” Ament says. The bill recognizes that we need to design infrastructure “taking into account two things: the needs of people, the movement of goods and people, but also the movement of wildlife,” he says. “And finally, we’re doing it.”
But what to build? The most influential examples of crossings in North America are found next to the Rocky Mountain Front in Canada. The area, which has the richest diversity of large mammals on the continent, is divided in two by the Trans-Canada Highway. In Banff National Park, a set of 44 wildlife steps (six steps above and 38 steps below) have been built to bridge the gap, creating a connected system used by a wide range of species, such as elk, cougars and coyotes, as well as rarer animals such as red foxes, grizzly bears, wolves, wolves, snakes, beavers, and lynxes.
But Banff’s wildlife footsteps, like most, suffer from a kind of horseless carriage syndrome, their designs being confined to existing infrastructure. Tunnels are usually poorly adapted culverts, pipes (usually made of concrete) that carry water under the roads. And overpasses have generally been taken on the bulk of the roads: they are built as if they were going to carry the weight of an 18-wheeled vehicle and then “dressed” in foliage, Lister says.
ANDREW MERRITT
A scattering of experiments are beginning to rethink this model. One is the Wallis Annenberg Wildlife Crossing, the $ 90 million wildlife bridge under construction in northern Los Angeles. Designed by architect Robert Rock, it avoids the humpback arch of older bridges in favor of a large flat expanse that only needs one column to support it between mountains and across a road traversed daily by about 300,000 cars. . It’s the “innovation poster,” says Renee Callahan, executive director of ARC Solutions, a group that researches how to build better wildlife bridges. “It’s literally designed for species, from mountain lions to mule deer and mice,” Callahan says. “They’re designing it down, literally, in the mycorrhizal layer, as far as the soil is concerned, to make sure that the soil itself has the network of fungi that can support the native vegetation.”
There are many unknowns as construction begins, especially how the different species will react to the large volume of vehicles passing below. The National Park Service will monitor the activity on the bridge, as well as the DNA profiles of the animals on both sides of the highway. Many are looking to see what will happen to the mountain lion population in the area. Over time, inbreeding has led to genetic abnormalities, such as a revealing twist in the tail of local cats. The agency predicted that the population would become extinct in decades without crossing.
In the United States, the $ 350 million infrastructure bill is well below what will be needed to deal with the fragmentation created by the country’s 4 million miles of public roads. But there are a handful of innovations that could tip the cost-benefit analysis by allowing steps to be built at a lower cost or in places where it was not previously feasible.
Currently, animal bridges are built only where there is protected land on either side of the road, as the typical expense of building a concrete bridge would be difficult to justify in a place that someone could develop in a few minutes. years. Lighter, cheaper modular systems could be used in places whose future is less secure, explains Huijser: “If the adjacent land becomes unsuitable for wildlife, we can dismantle it and move it.”
A candidate material for these modular systems is precast concrete. There is also enthusiasm for fiber-reinforced polymer (FRP), a less dense material than concrete that is made of resin-fixed structural fibers. The FRP has been used to build bridges by foot and bicycle in Europe and a fast and easy wildlife bridge in Rhenen, south of the Gooi, in the Netherlands. Currently, the Federal Highway Administration does not allow it to be used in traffic infrastructure in the U.S., but there is a growing demand for change. “These are barriers that are primarily about politics and governance. They’re not about science or technology,” says Lister.
