In the Cascade Range, the question isn’t why animals cross the road, but how they can do so without becoming salamander road-cakes or elk a la SUV.

The answer, say Washington state transportation officials and biologists, lies under and over a humming mountain highway.

In June, the state’s Department of Transportation released plans for widening a 15-mile section of I-90 east of Seattle, smack in the middle of a major wildlife thoroughfare. To reduce auto-animal collisions, the plans include several types of wildlife passages modeled after successful critter crossings in Arizona and Florida and on Banff’s Trans-Canada Highway (HCN, 2/7/05: Caught in the Headlights).

The road improvement project, slated to begin in 2011, will be a "showpiece" of ecological highway building, says Kim Vaughn, a transportation department design supervisor. Work could include improving culverts to aid smaller mammals and reptiles, creating hydrologic connections for fish and amphibians, and building the country’s first wildlife over-crossing, a wide bridge carpeted with native soil and plants. "We’re targeting a wide range of species, from low-mobility salamanders to large carnivores," Vaughn says.

Tony Clevenger, a Montana State biologist, says getting animals across safely is just the beginning: "Habitat is getting chopped up and biodiversity is getting scarcer." The real boon of the project, he says, will be reconnecting the wildlife living on both sides of I-90 in the Wenatchee National Forest.

So far, the state has committed $388 million to the highway improvements, most of which will go to road widening and avalanche-safe tunnels. That wildlife welfare is also addressed thrills Jen Watkins, a spokesperson for the I-90 Wildlife Bridges Coalition, which pushed for including animal crossings in the project: "It’s critical for us to attack the last barrier for wildlife." The public can comment on the project through Aug. 5.