The Trans-Canada Highway runs straight through Banff National Park \u2014 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.<\/p>\n
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\u2019s animal populations in two, a river of traffic no prudent animal would cross, splitting gene pools on either side of the pavement.<\/p>\n
Canada\u2019s answer, built out over three decades, was to give the animals their own infrastructure \u2014 and it has become the most-studied, most-copied piece of wildlife engineering on Earth.<\/p>\n
Six bridges, thirty-eight tunnels<\/p>\n
Along that one stretch of highway, Parks Canada built 44 crossing structures \u2014 six overpasses and 38 underpasses<\/a> \u2014 beginning with the first two overpasses in 1996 at about $1.5 million each.<\/p>\n 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 \u2014 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.<\/p>\n 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.<\/p>\n The numbers<\/p>\n 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<\/a> \u2014 and by 96 percent for elk and deer, the species that once died there most.<\/p>\n Cameras at the crossings have logged more than 250,000 animal passages<\/a> since monitoring began \u2014 the world\u2019s longest-running wildlife-crossing research program \u2014 by more than a dozen large species: grizzly and black bears, wolves, cougars, lynx, wolverines, moose, elk, deer, coyotes.<\/p>\n 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<\/a>. The wary species \u2014 wolves, grizzlies \u2014 took up to five years of sniffing, approaching and retreating before committing. But once a crossing enters a grizzly\u2019s 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 \u2014 a trail the next generation will treat as something that was always there.<\/p>\n The mating question, answered in hair<\/p>\n The deeper worry was never just roadkill. It was genetics \u2014 whether the fenced highway, even with crossings, would still split bears into two slowly inbreeding populations.<\/p>\n