New Diverging Diamond, Lane Widening Coming To State Route 18

SNOQUALMIE, WA — Travelers who frequent the Interstate 90/State Route 18 interchange will notice crews working in the area over the next several weeks, laying the groundwork for a major project that will last until 2025.

The Washington State Department of Transportation cautions that drivers should plan for more congestion in the area while contractors install work signage and begin to remove trees. The project will intensify late in the spring as crews begin to build a new diverging diamond interchange — only the second in all of Washington — designed to improve traffic flow and safety.

Officials expect crews will clear trees along the highway through March, which will be replaced by nearly 17,000 new trees at the end of construction.

"At least 382 of the felled trees will remain onsite and will be used to improve fish and wildlife habitat," WSDOT said. "Six culverts that are now barriers to fish passage will be removed, opening up access to 13 miles of fish habitat that is essential for salmon and steelhead."

According to WSDOT, the project will also see the highway widened to two lanes in each direction from the new interchange to two miles south. A separate project will widen the freeway to Issaquah-Hobart Road, with work slated to begin in 2025. Crews are also scheduled to construct several new bridges to improve the habitat for native wildlife and fish.

The $188 million project is fully funded by gas tax revenue and money from the "Connecting Washington" package.