Many of the massive bridges included in new state plans to widen Interstate 90 through Snoqualmie Pass will be for more than just people.

For the first time, the state is considering a series of massive culverts and overpasses to help wildlife — from elk and deer to cougars and lynx — traverse that treacherous ribbon of asphalt and get from the north side of the Cascades to the south.

Today, the state plans to release a draft of its half-billion-dollar-plus proposal to widen 15 miles of I-90 from four to six lanes from the top of the pass to Easton, Kittitas County. It will include options to straighten curves near Keechelus Lake and move highway lanes so avalanches are less likely to close the pass in winter.

And the plan also will lay out options for a series of 14 wildlife crossings, from small culverts to a 1,200-foot bridge, that would be among the first in the country designed to reverse some of the ecological damage wrought by highways that bisect wildlife habitat.

"Each of these is in areas where biologists say wildlife is likely to use them — because they've seen roadkill there, or the habitat is there," said Mark Pettit, a spokesman for the state Department of Transportation.

But the structures will come at a price. Pettit said state officials estimate the crossings will cost $25 million to $100 million combined.

"I really question the cost-benefit of this," said state Senate Minority Leader Bill Finkbeiner, R-Kirkland. "It seems to me that there's got to be cheaper ways to address this problem."

Information

Wildlife crossings: www.wsdot.wa.gov/Projects/I90/

HyaktokeechelusDam

Biologists in recent decades have learned that many mammals, such as wolves or grizzly bears, range over hundreds of square miles. If they are isolated in small areas, they are forced to inbreed, which causes genetic problems that make entire wildlife populations more susceptible to disease or predators.

Environmentalists and federal land managers since 2000 have raised millions of dollars and bought tens of thousands of acres of private land in the central Cascades so they would be preserved as a link between the Alpine Lakes Wilderness to the north and the Norse Peak Wilderness outside Rainier National Park.

But all that land is still segregated by I-90. So when DOT began planning to reconstruct a section near the top of the pass, environmentalists and the U.S. Forest Service got involved.

"This is a quantum leap forward," said Charlie Raines, an environmental activist with the Sierra Club.

Outside "Alligator Alley" — an aboveground causeway in Florida — and a massive wildlife overpass in Canada's Banff National Park, few wildlife crossings on this scale have been erected in North America.

Washington's versions are needed to help carnivores, especially those potentially facing extinction such as lynx and gray wolves, said Patty Garvey-Darda, a Forest Service biologist.

State Secretary of Transportation Doug MacDonald acknowledged a wildlife-friendly highway "will require a significant investment." But he recalled a four-person fatality last year outside North Bend when a driver and his passengers were killed after hitting an elk on the roadway.

Besides, he added, because I-90 cuts across national forest, "even if we didn't propose it, the Forest Service still would have made us do something like this."

Craig Welch: 206-464-2093 or cwelch@seattletimes.com