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I-90 Snoqualmie Pass East

I-90 Snoqualmie Pass East

Building a safer, more efficient, and reliable interstate
Snoqualmie Pass, Washington
Washington State Department of Transportation
Contract Value
$177 Million
Completion Date
Market Sector
Roadways & Bridges

The Washington State Department of Transportation (WSDOT) awarded Atkinson Construction this $177 million contract to widen I-90 from two to three lanes in each direction just east of the Snoqualmie Pass summit through the Cascade Mountain range.

Atkinson proposed a Cost Reduction Incentive Proposal (CRIP) to utilize the Draft Environmental Impact Statement Alternative #4, which substituted elevated side-by-side avalanche bridges for the contract Snowshed and benefited the project and WSDOT. The solution eliminated $37 million in long-term showshed operations and maintenance costs, minimizes construction impacts to the public, and increases the likelihood of achieving the project schedule. The twin 1,200-foot-long bridges rise over the avalanche chutes and can accommodate 100-year avalanche events to virtually eliminate road closures due to avalanche and snow removal.

The scope of work improved three miles of roadway geometrics through several curves and 4,600 LF of drainage. The project originally included an 1,100-foot-long bridge over the lakeshore. However, due to soil and rock conditions, this bridge and the associated Wall 7 was not constructible as originally designed. As a change order from WSDOT (Wall 7 Redesign), Atkinson and designer Jacobs performed an alternative analysis and proposed multiple design solutions. WSDOT chose a roadway geometric solution that eliminated the bridge and added two short retaining walls.

The project team blasted and excavated 400,000 cubic yards of rock and placed 116,000 tons of base course, 31,000 cubic yards of Portland cement concrete pavement, and 38,000 tons of hot mix asphalt (HMA). Atkinson built four single-span bridges to replace existing culverts to improve drainage and provide wildlife and fish passage.

Atkinson has proposed a new solution to the avalanche area, and that is to replace the snowshed with a bridge-type structure. This will allow the avalanches to go underneath the highway instead of over the highway like we had planned.
Brian White, Engineer, Washington State Department of Transportation