WSDOT will close SR 18 between I-90 and Issaquah-Hobart Road from 9 pm, Friday, Aug. 15, until 5 am, Monday, Aug. 18, 2025, to advance work on the widening of SR 18 and to perform annual road maintenance over Tiger Mountain.
Only local traffic to SE104th Street will be permitted south of I-90 during the closure. No vehicles will be allowed over Tiger Mountain summit.
Drivers are advised to 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 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 between I-90 and Deep Creek.
SR 18 widening 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 includes:
- Repair damaged guardrail
- Improve sign visibility
- Perform vegetation management
- Repave sections of the roadway
- Perform safety checks