Item: I-90 snoqualmie pass: evolution of an interstate highway avalanche program
Title: I-90 snoqualmie pass: evolution of an interstate highway avalanche program
Proceedings: 2010 International Snow Science Workshop
Authors: Craig Wilbour*, John Stimberis*, Washington State Department of Transportation
Abstract: Interstate 90 over Snoqualmie Pass, WA (921 m) is the major highway through the Cascade Mountains of Washington State. Snoqualmie Pass receives an average of 1100 cm of snowfall annually. I-90 is affected by 5 active avalanche areas containing nearly 40 individual paths. Increasing traffic volumes have exceeded the capacity of the 4 lane highway. Avalanche delays and closures have an economic impact that often exceeds several million dollars (USD), depending on the length of the closures. The current two-lane snow shed was built in 1950, and additional lanes were added in the 1960’s. These lanes are unprotected from avalanches. Avalanche control along I-90 over Snoqualmie Pass will be dramatically reduced by building passive defense structures. WSDOT has started a $595 million (USD) project to upgrade and expand an existing 8 km section of I-90. Plans include replacing the existing 2-lane 152 m snow shed with a 6-lane snowshed 335 m long. Approximately 1200 m of snow supporting structures will be installed in other avalanche starting zones. This will be one of the largest highway snow sheds and the most extensive fencing projects in North America.
Keywords: snow sheds, avalanche fences, explosives tramways, highways