Two bridges are planned to replace the snowsheds that protect drivers from avalanches on Interstate 90 near the summit of Snoqualmie Pass. The idea is that avalanches would slide beneath the freeway.

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YAKIMA — Every winter, frustrated drivers add hours to their trips across the state when Interstate 90 over Snoqualmie Pass is closed for avalanche control.

But a newly approved plan that continues major construction on the pass should help: The project will transform a section of the freeway into two 1,200-foot-long bridges, which will allow snow and debris to slide down the hillside and under the roadway, eliminating or drastically reducing those winter-avalanche delays.

“It’s designed to take the worst of the worst of the worst of everything,” said Phil Larson, a project manager for Guy F. Atkinson Construction, the contractor that pitched the bridge proposal in lieu of the state’s plan to replace the existing 500-foot snowshed that shields the roadway.

Construction this summer will include delays for rock blasting several nights of the week, but should otherwise have little effect on drivers, officials say.

The bridge proposal is the latest step in the state Department of Transportation’s long-term improvement work on Snoqualmie Pass, which began in 2010. The ongoing five-mile project will expand the freeway to three lanes in each direction, stabilize rock slopes and extend chain-up areas for trucks, to the tune of $551 million.

Construction underway encompasses the 2 ½ miles of freeway between Hyak, Kittitas County, and the western side of the snowshed. Spokane-based Max J. Kuney Construction is two years into that four-year project, and is set to finish on schedule in 2013.

For the next 2 ½-mile phase, transportation officials originally envisioned a replacement of the current tunnellike 62-year-old metal snowshed, which covers about 500 feet of the two westbound lanes.

The replacement would have been 1,200 feet long and stretched over all six lanes of the revamped interstate, spanning the five avalanche chutes that cause the bulk of winter problems.

But when Atkinson won the bid, the company offered an alternate plan: two raised bridges, high enough that avalanches could slide underneath.

The bridges eliminate federally required safety measures inside the snowshed, such as adequate ventilation, lighting and fire protection.

“Everyone saw immediately the benefits of not having a long-term operating and maintenance risk of a snowshed and its electrical and mechanical systems,” said Bob Adams, vice president of Atkinson. Cost savings are estimated to be $650,000 a year.

This week, the Transportation Department will give the company the official go-ahead to begin construction.

The construction site runs from the west side of the snowshed to just beyond Keechelus Dam.

It’s not scheduled to be completed until 2017, so drivers can expect some level of disruption from April through October every year until then.

But the company is committed to keeping two lanes of traffic open in each direction at peak travel times, says Brian White, assistant regional administrator for I-90 construction.

“We’ll try to minimize the effect to the public as much as we can,” he said.

On weeknights this summer, he said, drivers should check the department’s website before traveling across the pass, as crews will be blasting several nights a week.

The blasting starts an hour before dusk, and the freeway is generally closed for about an hour each time.