State Route 18 will close in both directions between I-90 and Issaquah-Hobart Road from 9 p.m. Friday, August 15, to 5 a.m. Monday, August 18. No vehicles will be allowed to cross the Tiger Mountain summit during this time, with access restricted to local traffic only south of I-90.
The Washington State Department of Transportation (WSDOT) is coordinating multiple projects during the closure, all aimed at improving the safety and flow of traffic along this busy corridor.
Drivers should plan ahead, use alternate routes, and expect delays. Semi-trucks and freight traffic are advised to detour via I-405 and I-90, as local routes such as Issaquah-Hobart Road are not suitable for large vehicles.
Contractor crews will use the closure to continue work on the I-90/SR 18 Interchange Improvements project, which is expanding SR 18 to two lanes in each direction between Lake Creek and Deep Creek.
Planned activities include grinding and paving, installing guardrail, hydroseeding, and removing temporary barriers. These improvements are part of a long-term project scheduled for completion in fall 2025.
In addition to construction, WSDOT maintenance crews will conduct annual work during the closure. This includes repairing guardrails, repaving, improving signage visibility, trimming vegetation, and performing general safety checks—all tasks that benefit from a full highway shutdown.
By combining construction and maintenance into one weekend closure, WSDOT aims to minimize future disruptions for travelers.
For updated information on detours and project progress, visit wsdot.wa.gov.
