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Officials to close I-90 for avalanche control
By JOHN CRAMER of the Missoulian

Interstate 90 near Lookout Pass will close temporarily Tuesday morning while highway officials try to trigger and clean up avalanches before they occur naturally.

Many modes of transportation have shut down over the years because of Montana's winter weather - airports, roads, railroads - but it will be the first time in state history that pre-emptive avalanche work closes an interstate highway.

At 10 a.m., the Montana Department of Transportation will close a five-mile stretch of I-90 between the Saltese and Taft interchanges near the Montana-Idaho border west of Missoula.

Two avalanche specialists will detonate charges in an effort to cause unstable snow to break loose from steep slopes above a 1,000-foot stretch along the interstate, said Doug Moeller, MDOT's maintenance engineer in Missoula.

The specialists will ski along the ridgeline, light fuses on 2-pound charges and toss them over the edge, a common practice along highways in Colorado, Washington and other Western states.

Unpredictable weather ruled out using a helicopter to drop the charges on Lookout Pass.

The length of time the highway will be closed will depend on the amount of snow, trees and rocks that fall on the highway and how long it takes to remove it.

There's a chance that no avalanche will break loose, but officials expect some snowslides will occur and that it will take from one hour to 12 hours to remove.

“It's not an exact science, so we're not quite sure,” Moeller said.

A dozen MDOT workers and a fleet of snowblowers, snowplows, graders and loaders have been assembled to tackle the job on both sides of the interstate.

With the snowpack above normal at Lookout Pass and many other mountain sites in western Montana, avalanches have been occurring periodically on roadways and ski slopes.

More than 9 feet of snow has settled along I-90 and even more at higher elevations above the interstate.

A small avalanche occurred Sunday on the Montana side of Lookout Pass, dumping a 75-foot swath of snow about 4 feet deep on I-90 and temporarily halting traffic in the area where Tuesday's avalanche control work will take place.

MDOT crews have been working constantly to keep the pass safe for travelers, but officials decided to take a pre-emptive approach by detonating the unstable snowpack above the pass.

Other sections of I-90 might be closed for more avalanche control work later this winter, but no final decision has been made.

“When we blow this one, we'll get an indication of how the others will react,” Moeller said.

In 1996, the last big snowfall in western Montana, an avalanche blocked all four lanes of I-90, the last time snow severely interrupted the interstate.

Closing the interstate will do more than temporarily inconvenience thousands of travelers.

Larry Swanson, director of the Center for the Rocky Mountain West at the University of Montana, said shutting I-90 for an extended period could interrupt the flow of interstate goods by tractor-trailers.

Lookout Pass is a major east-west route for big rigs, and companies that transport their freight by trucks depend on tight shipping schedules - in effect using the trucks as rolling warehouses rather than keeping their inventory in storage facilities, he said.

“That puts a lot of pressure on the timing of shipments, so closing down the interstate is a big deal because there aren't a lot of alternatives” for east-west truck traffic in this part of the Northwest, Swanson said.

Reporter John Cramer can be reached at 523-5259 or at johncramer@missoulian.com.

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