Project expected to wrap up construction in 2026
SNOQUALMIE – Eastbound and westbound State Route 18 reopened Monday, Oct. 20, with two lanes in each direction between Interstate 90 and Deep Creek, ushering in improved traffic flow and safety along a 2-mile stretch at the northern end of the SR 18 corridor.
The opening marked a significant milestone for the I-90/SR 18 Interchange Improvements project. The new, widened SR 18 removes a pinch point that has created congestion at the I-90/SR 18 interchange since long before contractor crews working for the Washington State Department of Transportation opened a diverging diamond interchange in July 2025.
Though construction began to widen this section of SR 18 in 2023, traffic did not shift into its final configuration until a four-day closure of the highway, which wrapped up early Monday, Oct. 20. To add the new eastbound and westbound lanes, crews constructed new four-lane bridges that improved fish passage along Lake Creek and Deep Creek beneath SR 18 and a new two-lane bridge over Raging River next to the existing bridge.
Though traffic is in its final configuration along SR 18 and through the diverging diamond interchange, construction will continue into 2026.
Improved traffic flow
The new diverging diamond interchange was designed to work with the additional lanes of SR 18 to improve traffic flow and safety through the corridor. The new lanes eliminate a pinch point a few hundred feet south of I-90. Traffic from Snoqualmie Parkway and the eastbound and westbound I-90 off-ramps no longer funnel down to a single lane to use westbound SR 18 toward Auburn.
Before the new SR 18 lanes opened, the pinch point created congestion through the interchange during busier travel times, such as the evening commute and Sunday afternoons. Those high traffic volumes clogged the interchange and backed up traffic on both off-ramps and onto mainline I-90.
WSDOT expects congestion and backups at the I-90/SR 18 interchange will reduce now that SR 18 is in its final configuration between I-90 and Deep Creek. The SR 18 widening work ties into the westbound truck climbing lane just south of Deep Creek, meaning SR 18 will be two lanes to Tiger Mountain summit. This gives westbound traffic approximately 4 miles to calm and merge into a single lane.
Crews also installed a permanent center barrier between eastbound and westbound SR 18 that will help improve safety through the corridor. That barrier stretches from north of the Lake Creek bridge to south of the Deep Creek bridge.
Project completion
People traveling through the area should continue to expect periodic daytime and nighttime lane reductions and ramp closures along SR 18 and at the diverging diamond interchange this fall. Details for those closures will be shared as they are scheduled on WSDOT’s real-time travel map, the WSDOT app and the project webpage.
Though this is another significant milestone for people who travel through the I-90/SR 18 interchange, the $188 million project still has several tasks to complete, including:
- Final paving through the I-90/SR 18 diverging diamond interchange, including the I-90 on- and off-ramps.
- Final paving along both directions of SR 18 between I-90 and Deep Creek.
- Permanent lane striping.
- Installing landscaping, curbs and guardrail.
These tasks and other minor items are scheduled to be completed in 2026 once weather improves.