Both directions of SR 18 to close Aug. 15-18 over Tiger Mountain summit for repairs and improvements

SNOQULAMIE –Think of State Route 18 as a Double Stuf Oreo the weekend of Aug. 15-18 – the best part, at least for travelers, will be in the middle. 

A trio of Washington State Department of Transportation maintenance and construction projects improving different sections of SR 18 require weekend closures on each end of the highway. From a full closure of SR 18 over Tiger Mountain summit to directional closures of the highway in Auburn, travelers should seek alternate routes and expect delays.

Here’s a look at what’s happening:

SR 18 closure over Tiger Mountain summit

From 9 p.m. Friday, Aug. 15, to 5 a.m. Monday, Aug. 18, eastbound and westbound SR 18 will close between I-90 and Issaquah-Hobart Road. Only local traffic to Southeast 104th Street will be permitted south of Interstate 90 during the closure. No vehicles will be allowed over Tiger Mountain summit. 

People should seek alternate routes. Freight traffic should use I-405 and I-90 throughout the weekend. Issaquah-Hobart Road and Issaquah city streets are not suitable for semi-trucks.

During the closure, contractor crews will advance work on new lanes of SR 18 between Lake Creek and Deep Creek. The work is part of the I-90/SR 18 Interchange Improvements project, which is widening a 2-mile stretch of SR 18 to two lanes in each direction. Work includes:

• Leveling and preparing the new lanes for a final layer of asphalt
• Milling and grinding asphalt
• Installing guardrail
• Landscaping, including mulching and hydroseeding
• Removing temporary barriers

Once the SR 18 widening work finishes in fall 2025, the new lanes will work with the recently opened I-90/SR 18 diverging diamond interchange to improve traffic flow and safety through the corridor. 

SR 18 maintenance

During the weekend closure of SR 18 between I-90 and Issaquah-Hobart Road, WSDOT maintenance crews also will perform annual work on the highway over Tiger Mountain summit. Tasks include:

• Repair damaged guardrail
• Improve sign visibility
• Perform vegetation management
• Repave sections of the roadway
• Perform safety checks

This work is scheduled to occur with the I-90/SR 18 work. This helps limit the number of SR 18 closures over Tiger Mountain summit.

Westbound SR 18 closures in Auburn

The same weekend, crews are replacing westbound SR 18 expansion joints on the C Street Southwest bridge as part of a pavement repair project. Here are the closure details:

• From 11 p.m. Friday, Aug. 15, to 1 a.m. Sunday, Aug. 17, the right lane of westbound SR will close between M and C Streets Southeast. The Auburn Way South on-ramp to westbound SR 18 will close at the same time. A signed detour for the ramp closure will use city streets to the C Street Southwest on-ramp to westbound SR 18.
• From 2 a.m. Sunday, Aug. 17, to 5 a.m. Monday, Aug. 18, westbound SR 18 will close at Auburn Way South. All westbound vehicles will exit at the Auburn Way South off-ramp and use the on-ramp to return to westbound SR 18. Police officers will direct people through the intersection between the on- and off-ramps.

Eastbound SR 18 through Auburn will remain open. People should expect delays, especially during peak travel times.