Avalanche chutes turned out to provide the extra clearance needed to allow bridges—not snowsheds—to grace the final design of a five-mile Interstate 90 improvement project east of Snoqualmie Pass in Washington.
With 62-year-old snowsheds already in place protecting only westbound lanes, the Washington State Department of Transportation needed to replace them anyway. The department had originally hoped for bridges (even ones that would have crept into Keechelus Lake) to work as the solution, but the fear of whiteouts and avalanches making engineering too tricky on the bridges resulted in experts recommending a wider and long snowshed.
But WSDOT didn’t give up. It wanted bridges.
After months of collaboration with contractors and engineers, crews devised two, three-lane bridges built high enough to accommodate avalanche chutes and digging into the chutes and channeling them to go under the new bridges.
The cost of the final two-mile stretch will run about $180 million, but construction costs of building bridges is the same as a new snowshed and will save about $650,000 per year in snow-related maintenance, or nearly $49 million over 75 years, according to WSDOT. The bridges will avoid costs associated with fire- and life-safety systems in the snowshed, as well as electricity and ventilation.
“This bridge solution in this avalanche-prone area helps keep the highway more operational in the wintertime, and also saves a significant amount of money,” says Paula Hammond, secretary of the Washington State Department of Transportation.
Total cost of the five-mile project from Hyak to the Keechelus Lake area is $551 million. Guy F. Atkinson Construction was selected to build the final two miles of the project, which is widening the highway from four to six lanes, and replacing the snowshed. Max J. Kuney Inc. is constructing the first three miles of the project. The entire five-mile project is scheduled for completion in 2017.
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