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A well-beaten trail leads to an overpass eight metres above the Trans-Canada Highway in Banff, where vehicles whiz beneath at a rate of 24,000 a day in the busy summer tourist season.

But this 50-metre-wide structure, covered with grass, trees and rocks and carefully designed to reduce road noise for those treading on it, is normally off-limits to people. An exception is made for a reporter today, and for researchers studying how wildlife-crossing structures like this one help bears, cougars, wolves, deer, elk and other critters traverse the highest-volume artery to cut through any national park on the continent.

Gazing down at the traffic speeding underfoot, conservationist Nicky Blackshaw says, “Imagine a mother bear with her cubs trying to get across.”

The inadvertent game of chicken in the search for food, mates and dens used to end in 800 collisions a year in Banff. Then Parks Canada began erecting wildlife-crossing structures, as well as fencing along the highway. Now, 24 wildlife crossings, both underpasses and overpasses, have helped reduce animal mortality by 80 per cent and scientists have recorded animals using the structures more than 90,000 times since 1996.

“There were comments in the beginning that these didn't work,” said Ms. Blackshaw, who is lobbying to build similar structures along a 3,200-kilometre swath of land stretching from Wyoming's Yellowstone National Park to Yukon, a stretch of Rocky Mountain terrain dubbed Y2Y. “These are great.”

Now, scientists are trying to determine just how many individual bears – a bellwether indicator for how the ecological integrity of the wilderness is faring – are using the crossings. They are employing old-fashioned barbed wire strung across the corridors to snag bits of fur so that high-tech DNA analysis can determine the number of males and females in the park and how they are related.

“We are fingerprinting them,” explained Michael Sawaya, a wildlife biologist with the Western Transportation Institute at Montana State University who is in the midst of the three-year study conducted in co-operation with Parks Canada. “We know that these crossings are being used, but how many individuals are using them?”

In the 1980s, Parks Canada officials set out to reduce the number of collisions with wildlife, ordering construction of wildlife crossings along the highway. Two overpasses, costing $2.5-million each, and 22 underpasses, which include culverts or open-span bridges, were completed in 1996. It is considered the largest and most diverse collection of wildlife crossings in the world. It is also the most studied, largely as the result of the work of Tony Clevenger, a wildlife ecologist who was hired by Parks Canada more than a decade ago.

Using infrared cameras and examining prints from paws or hooves left in sand-filled track beds, he found that 10 species of large mammals were using the corridors.

The vast majority of passes involve deer and elk, but carnivores also used them thousands of times to seek refuge from the road. But it is the more than 1,000 black bear passes and 400 grizzly passes that are the focus of Mr. Sawaya's current research.

Banff officials estimate there are perhaps 60 grizzlies roaming inside the park boundaries and maybe as many (but likely fewer) black bears.

Since roadways reduce access to habitat and limit genetic diversity by cutting off potential mates, finding out the total number of animals may go a long way to assessing what impact these structures have in propping up the species.

Dr. Clevenger, a senior research scientist with Montana's Western Transportation Institute, launched a pilot project in 2004 to capture fur samples.

The technique recently was used to count grizzlies living in the Foothills and southeastern slopes of the Rockies. That resulted in a report last summer that pegged the number of grizzlies at fewer than 100 east of Banff and perhaps 500 in the entire province. Both numbers are so low that conservationists say the species could disappear from Alberta.

The health of the park depends on the health of the bear population, especially grizzlies, said Marjorie Huculak, a spokeswoman with Parks Canada in Banff. “Good science leads to good decision-making,” she said.

While officials in some jurisdictions haven't invested in crossing structures, saying they need more evidence that the corridors maintain or revive wildlife populations, others like what they've seen in Banff and are replicating it.

Continuing work on the twinning of the highway farther west by Lake Louise was supposed to include another 17 crossings, but the number was cut to eight when construction costs escalated in the booming Alberta economy.

This fall, Waterton Lakes National Park in the southwest corner of the province is planning to install four tunnels to help the survival of long-toed salamanders, which have been squished by the hundreds as the 13-centimetre-long amphibians try to cross the road to and from their breeding ground.

In the last 15 years, people have started to recognize the impact of roads, Mr. Sawaya said. In Banff, researchers have noticed that animals are increasingly using the crossings and passing the knowledge on to their young.

As he dips down into the underpass to check for fur and tracks, Mr. Sawaya said he captured video footage of two wolves trotting through here. Last month, wolf pups were caught on film using another tunnel, and loads of pictures have been snapped of bears using the passageways with their cubs.

“One of the technicians ran into a grizzly bear here the other day,” he said.