SR 18 Widening Nears Finish Line with Four-Day Tiger Mountain Closure

Contractor crews will close State Route 18 over Tiger Mountain for four days starting Thursday, Oct. 16, to expand the highway to two lanes in each direction. The closure will take place from 9 p. m. Thursday to 5 a.

m. Monday, restricting traffic between Issaquah-Hobart Road and I-90, with only local access to Southeast 104th Street allowed. The Washington State Department of Transportation (WSDOT) aims to alleviate congestion at the I-90/SR 18 interchange, where traffic currently funnels down to a single lane, causing backups during peak hours. This work is part of the I-90/SR 18 Interchange Improvements project, which also opened a diverging diamond interchange in July 2025. WSDOT expects that the new lanes will significantly improve traffic flow and safety through the corridor.

The project will also include paving transitions, lane striping, and installing barriers. Weather conditions may affect the schedule, as much of the work requires dry weather. Final project completion, including landscaping and permanent lane striping, is projected for 2026.