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High in the Colorado Rockies, Interstate 70 crests over Vail Pass, cutting a four-lane asphalt slash through the sur-rounding national forests that carries 20,000 cars and trucks daily. In recent years dozens of animals have been killed trying to cross I-70, which bisects Colorado from east to west, including black bears, deer, elk, and the endangered Canadian lynx.

Now a safe route for four-footed travelers is in the making. Colorado’s Department of Transportation (CDOT) has received $420,000 in federal highway funds to study a proposal for a wildlife bridge at West Vail Pass. The money has not yet been set aside to build the span, which the agency says could cost up to $12 million. The actual price tag won’t be known until consultants submit a final design to the CDOT, which could happen as soon as 2008. Environmental groups that lobbied for the initial research funds are working to broaden state and federal support for the bridge.

In addition to reducing collisions, supporters say the overpass would enlarge animals’ ranges. “Highways prevent species from accessing their historic migration and breeding areas, which reduces their genetic diversity,” says Amy Masching, a conservation biologist with the Denver Zoological Foundation. “This is a wildlife-rich area, so it’s a really important site for connectivity.” To buttress their case, volunteer monitors in the past year have used motion-triggered digital cameras to take more than 400 photographs of wildlife activity in the five-mile zone targeted for the overpass, including shots of deer, coyotes, elk, black bears, red foxes, pine martens, and porcupines. The CDOT will use the data to document migration patterns around the proposed site for the overpass.

The North American prototype for wildlife crossings is Canada’s Banff National Park, where animals traverse the Trans-Canada Highway via 22 underpasses and two overpasses. Research at Banff suggests that some large animals, such as elk, moose, wolves, and grizzly bears, are more likely to use overpasses; black bears and cougars seek out more heavily forested environments and seem to prefer tunnels to wide-open bridge spans. Like the Banff overpasses, the Colorado bridge would be planted with vegetation to blend in with surrounding lands and to reduce noise and lights from the traffic flowing underneath.

A span over heavily trafficked I-70 in this popular vacation area would be more visible than most wildlife crossings in the United States, the majority of which are culverts and underpasses (there are overpasses in Utah and Florida). Advocates are lobbying for similar projects elsewhere, including a proposed crossing over Interstate 90 east of Snoqualmie Pass in Washington’s Cascade Mountains. “This is an emerging field and an important direction for transportation, so we’re staying in touch with other states,” says Monique DiGiorgio of the Southern Rockies Ecosystem Project, which is advocating for the Vail overpass. “Whatever we learn from this project needs to be communicated to everyone else.”—Jennifer Weeks
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