Work is under way on a $571-million upgrade to a mountainous, five-mile stretch of Interstate 90 - Washington’s busiest east-west connector.

Located miles from Seattle, the scenic highway, which is part of Snoqualmie Pass, weaves through the Cascade Range. The Washington State Dept. of Transportation’s comprehensive plan calls for widening the road from four lanes to six, repaving it with freeze- and thaw-resistant concrete, straightening curves, stabilizing rock slopes, and adding a chain-up area and 1,200-ft.-long snowshed. Moreover, WSDOT will add or replace four bridges and build four new ones bridges and culverts in an effort to improve fish and wildlife mobility.

Since I-90 carries 27,000 vehicles per day and $500 billion worth of goods annually, the improvement project is critical, says WSDOT. “This is an important step toward making I-90 a safer, more reliable transportation corridor for freight and the traveling public,” says Project Director Randy Giles.

WSDOT divided the project into three contracts. The first contract, awarded to WHOM KLB Construction of Mulkiteo, Wash., and totaling $3.3 million, entailed construction of a detour bridge and excavation, which was completed in 2009, says Amanda Sullivan, WSDOT spokeswoman.

Max J. Kuney Co., based in Spokane, Wash., is currently working on a three-mile stretch—bordered by a mountain and lake—under the second $76-million contract. In addition to constructing five bridges, this portion of the project calls for blasting one million tons of rock to push the mountain farther back from the road and to reduce fall hazards, says Will Smith, WSDOT project engineer. Two lanes remain open to traffic.

The third contract, worth between $150 million and $200 million, goes to bid in February 2011 and includes work on the final two miles, with completion scheduled for 2016.