Canada built 44 bridges and tunnels across a single stretch of highway so that animals could cross without dying, and collisions with wildlife there have fallen by more than 80%, with grizzly mothers now teaching their cubs to use the crossings like a route the family has always known

The Trans-Canada Highway runs straight through Banff National Park — 82 kilometers of four-lane road through the Canadian Rockies, carrying a vehicle every few seconds through some of the richest wildlife country on the continent.

For decades, the arithmetic of that arrangement was written in carcasses. The highway killed elk, deer, bears and wolves at a relentless rate, and did something quieter and worse besides: it cut the park’s animal populations in two, a river of traffic no prudent animal would cross, splitting gene pools on either side of the pavement.

Canada’s answer, built out over three decades, was to give the animals their own infrastructure — and it has become the most-studied, most-copied piece of wildlife engineering on Earth.

Six bridges, thirty-eight tunnels

Along that one stretch of highway, Parks Canada built 44 crossing structures — six overpasses and 38 underpasses — beginning with the first two overpasses in 1996 at about $1.5 million each.

The overpasses are the famous ones: to a driver they look like ordinary concrete bridges, until you glimpse the top and see forest running unbroken across them — trees, shrubs and grass planted fifty meters wide, a strip of the Rockies carried over four lanes of traffic. The underpasses do the volume work below: culverts and tunnels sized for everything from cougars to moose.

The third component is the one that makes the other two function: fencing along both sides of the entire stretch. The fence keeps animals off the road; the crossings give the fence somewhere to deliver them. Neither works alone. Together, they turned the highway from a wall with a kill rate into a permeable line.

The numbers

The results are the benchmark every road ecologist now quotes. Wildlife-vehicle collisions along the fenced, bridged stretch have fallen by more than 80 percent — and by 96 percent for elk and deer, the species that once died there most.

Cameras at the crossings have logged more than 250,000 animal passages since monitoring began — the world’s longest-running wildlife-crossing research program — by more than a dozen large species: grizzly and black bears, wolves, cougars, lynx, wolverines, moose, elk, deer, coyotes.

And the adoption curve turned out to be a personality test. Elk, bold and unbothered, used the overpasses before construction crews had even finished them. The wary species — wolves, grizzlies — took up to five years of sniffing, approaching and retreating before committing. But once a crossing enters a grizzly’s mental map, it stays there: monitoring has recorded female grizzlies bringing cubs across the structures, the route passing from mother to cub as learned family geography — a trail the next generation will treat as something that was always there.

The mating question, answered in hair

The deeper worry was never just roadkill. It was genetics — whether the fenced highway, even with crossings, would still split bears into two slowly inbreeding populations.

A Montana State University team answered it with barbed wire strung at the crossings, snagging hair from passing bears for DNA. The genetic analysis showed bears not merely crossing but breeding across the highway — among crossing bears, 47 percent of black bears and 27 percent of grizzlies successfully bred, including one enterprising black bear male who fathered at least 11 cubs with five females while commuting between both sides. Gene flow, the thing the highway had severed, was measurably restored — for wolverines and grizzlies alike, the fragmentation problem dissolved.

The export

Banff’s structures now cost $2 to 4 million per overpass, and for years the price tag was the argument against them. The park’s three decades of data ended that argument: collisions with large animals are expensive too — in vehicles, injuries and lives — and an 80-plus percent reduction pays the mortgage.

So the model travels. Banff’s findings shape highway projects across Canada, the United States — including the giant Wallis Annenberg crossing over ten lanes of Los Angeles freeway — and schemes from Costa Rica to Asia. The park that started with two experimental bridges in 1996 has become the reference dataset for a global retrofit of the road network.

The elegance of the whole thing is that nothing about it required the animals to change. The highway was the intruder; the crossings simply restored, in concrete and planted soil, the routes that were there before the asphalt — which is why the grizzly cubs following their mothers over the traffic aren’t learning anything new. They’re inheriting the old map, with one modern edit: the valley now includes a bridge, and the bridge, as far as the bears are concerned, has always been there.

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