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Washington State Department of Transportation
Northwest Region – 15700 Dayton Avenue – Shoreline, WA 98133 – 206-440-4000
TRAVEL ADVISORY
Oct. 14, 2025
Contact: David Rasbach, communications, 206-719-0603 (mobile)
SR 18 to close over Tiger Mountain for four days beginning Thursday night, Oct. 16, for widening
SNOQUALMIE – Eastbound and westbound State Route 18 will close for four days over Tiger Mountain beginning Thursday night, Oct. 16, to shift the highway into its final configuration between Interstate 90 and Deep Creek.
When SR 18 reopens early Monday, Oct. 20, the highway will be two lanes in each direction for more than 2 miles south of I-90.
Much of the work requires dry weather, and the closure may need to be rescheduled if too much rain is forecast.
What to expect
From 9 p.m. Thursday, Oct. 16, to 5 a.m. Monday, Oct. 20, no eastbound or westbound SR 18 traffic will be allowed between Issaquah-Hobart Road and I-90. Only local access traffic to Southeast 104th Street will be permitted south of I-90 during the closure, and no vehicles will be allowed over Tiger Mountain summit.
A signed detour will use SR 169, I-405, SR 900 and I-90, and people should consider other routes. Freight traffic should use I-405 and I-90 throughout the four-day closure and avoid Issaquah-Hobart Road and Issaquah city streets, which are not suitable for semi-trucks.
During the closure, crews will:
- Pave transitions.
- Stripe lanes in the new configuration with two lanes in each direction.
- Install required barrier and guardrail.
- Shift SR 18, including the intersection with Southeast 104th Street, into its final configuration.
Improved traffic flow
The work is part of the I-90/SR 18 Interchange Improvements project, which also opened a diverging diamond interchange in July 2025. The new interchange was designed to work with the additional lanes of SR 18 to improve traffic flow and safety through the corridor.
The new lanes will eliminate a pinch point a few hundred feet south of I-90. WSDOT expects congestion and backups at the I-90/SR 18 interchange to reduce once SR 18 is placed in its final configuration.
Construction is expected to finish in 2026, when a top layer of asphalt will be placed throughout the diverging diamond interchange and the new lanes of SR 18.
Real-time travel information is available via the WSDOT mobile app, the WSDOT travel map or by signing up for WSDOT's email updates.
Hyperlinks within the release:
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WSDOT keeps people, businesses and the economy moving by operating and improving the state's transportation systems. To learn more about what we're doing, go to www.wsdot.wa.gov/news for pictures, videos, news and blogs. Real-time traffic information is available at wsdot.com/traffic.
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