Concrete Progress is an ongoing series of columns by Peter Brewitt devoted to exploring America’s infrastructure. It is part of Orion’s Reimagining Infrastructure project.

The first thing I want you to do, before you read the rest of the column, is to watch this video. You can do it with the sound off, if you’re at work. It’s a little over two minutes. Don’t worry, I’ll wait. You won’t be sorry.



That ursine dance party was held in a provincial park in Alberta, Canada, not far from the town of Banff. While the video is delightful in and of itself (but what’s so special about that one tree?), the incredible collection of charismatic megafauna is pretty much par for the course in that stretch of Canada. The Northern Rockies host the last strong concentration of large mammals in North America. My wife spent a week in Banff not long ago, to take an intensive statistics course (fun!) and saw, without going to all that much effort, the following animals: grizzly bear, wolverine, moose, pika, elk, porcupine, snowshoe hare, great gray owl, northern goshawk, and a host of smaller or more common species. Banff is a Canadian Noah’s ark.

The animals (and the scenery) draw three or four million people to Banff National Park every year: it’s in the same league as Yellowstone or Yosemite. But this popularity, combined with the massive Trans-Canada Highway, which runs through Banff, means that the animals sometimes get hit by cars. This is tragic not just for the wildlife but also for people, especially if the mammal in the windshield is a moose. For a while, cars killed 150 large animals there every year. But I’m happy to report that Banff is reimagining its infrastructure and allowing elk, bears, and cars to travel through the mountains in comfort and safety.

The key is animal crossings. Forty wildlife crossings—underpasses and overpasses—now span the Banff stretch of the Trans-Canada Highway. They have been used hundreds of thousands of times by eleven different mammal species, and have reduced collisions by 80 – 90 percent. It has demanded some clever engineering—animals don’t use zebra crossings (despite the name) so you can’t simply paint one on the blacktop. Cougars and black bears, for example, prefer to squeeze discreetly through small underpass tunnels, but a moose or a wolf would find the idea absurd—they walk out in the open. The overpasses are planted with vegetation, bridging the road with a thin strand of replicated habitat. Even wolverines have been videoed using an overpass. And they’re especially popular with bears. Montana State University researchers have analyzed hair samples and found that 20 percent of the black and grizzly bears in the area use road crossings. In other words, the crossings have been a smashing success.

The benefits of these crossings go beyond the animals who might be killed on the road and extend to the animals who might not cross the road at all. Roads chop landscapes into archipelagoes, with islands of habitat separated by frightening barriers that only a few individuals and a few species are willing to cross. Smaller islands of habitat, whether they’ve been delineated by water or by asphalt, cannot support as many species as larger islands, and are more likely to drive large species, which need more space, to extirpation. If you exclude wolves, say, from an area, then populations of their prey animals—elk, deer, moose—will explode, with ripple effects extending to the plant species that they eat, the other animals that depend on these plants, and, eventually, a transformed landscape with different drainage and even soil chemistry. I should note that Yellowstone National Park, a day’s drive to the south, is seeing some of this action in reverse now that wolves have reestablished themselves there. Road crossings can help maintain healthy mammal populations, and the mammals keep their landscapes healthy. We’re making islands out of much of the world—I urge you to check out David Quammen’s important book Song of the Dodo if you’re interested in this stuff. Of course, modern civilization would not be possible without asphalt, but this means that the ecologically isolating effect of development is everywhere.

Of course, collisions are everywhere, too. Where I’m from in New Hampshire, the bumper stickers say “brake for moose.” Where I used to live in Yosemite, the roads are marked with red bear symbols for each place a bear has been killed by a car. In New Jersey, more than 30,000 deer are killed by drivers each year—and a deer can total a car. Animals and roads are a bad combination—it’s just a little starker in Banff, with its four million tourists and transcontinental highway and fairy-tale wildlife.

The question always arises: can you do this other places? You can. Here in California, underpasses allow desert tortoises to trudge safely around San Bernardino County. Across the ocean in Britain, they’re building underpasses for hedgehog and badgers. In Pennsylvania, they even have them for toads. What it takes is a community that is willing to invest in habitat connectivity—and in reducing highway accidents. But many communities are making it happen, digging tunnels, building bridges, and helping bears get to dance parties on the other side of the road.

Peter Brewitt has wondered about infrastructure ever since a flood kept him away from three days of kindergarten. He’s currently at work on a PhD at the University of California, Santa Cruz, where he’s researching the ways people restore and remake their environments.