SR 18 at I-90 to Close 5 Days, Expect Major Delays | Columbia Basin

SNOQUALMIE — State Route 18 will close in both directions at the Interstate 90 interchange near Snoqualmie for five full days beginning the night of Thursday, May 15, as part of a major construction push by the Washington State Department of Transportation. The closure, which runs continuously through 5 a.m. on Wednesday, May 21, is intended to significantly accelerate progress on the I-90/SR 18 Interchange Improvements project by allowing crews to complete nearly three months of scheduled work in less than a week. Originally planned as a series of weekend and overnight closures, WSDOT opted for the extended shutdown to minimize the long-term disruption and keep the project on track for a summer opening of the new diverging diamond interchange.

During the closure, crews will remove existing pavement, install new drainage and electrical infrastructure, rebuild and pave the southern portion of the interchange, construct new concrete islands and curbs, and build new traffic features including a left-turn lane onto Southeast 104th Street and a signalized U-turn allowing eastbound SR 18 drivers to head back west. No vehicles will be permitted to pass under the I-90 bridges during the closure. The timing was selected to avoid conflict with Mother’s Day and Memorial Day traffic surges.

While I-90 itself will remain open, access to SR 18 will be heavily restricted. Eastbound I-90 off-ramp traffic will only be able to turn right onto westbound SR 18, and westbound I-90 off-ramp traffic may only continue onto Snoqualmie Parkway or westbound I-90. No left turns will be allowed from either ramp. Eastbound SR 18 traffic will need to detour via I-90, looping around exits 22 or 27. Similarly, traffic from Snoqualmie Parkway must use I-90 to reroute. Emergency services, school district buses, and Sound Transit buses will retain access through the work zone.

WSDOT is advising all travelers to expect delays, consider alternate routes, and plan for extra travel time during the closure. Freight haulers on westbound I-90 are being directed to use Exit 22 or continue to I-405 rather than diverting through Issaquah city streets or Issaquah-Hobart Road, which are not suitable for heavy truck traffic.

The full closure is a critical milestone for the interchange project, as completing the southern section will allow work to shift to the area beneath the I-90 bridges and the northern segment of the new diverging diamond design. Once finished later this summer, the interchange is expected to improve traffic flow, reduce congestion, and enhance safety for the thousands of vehicles passing through the corridor daily.