Both directions of State Route 18 will close around the clock for more than five days beginning Thursday night, May 29, near Interstate 90 to build the southern end of a new diverging diamond interchange.
This extended closure should allow crews to complete the interchange portion of the I-90/SR 18 Interchange Improvements project this summer. Travelers should seek detour routes and add extra travel time to their plans during the closure.
SR 18 closure details
From 9 p.m. Thursday, May 29, through 5 a.m. Wednesday, June 4, traffic will not be allowed in either direction on SR 18 beneath the I-90 bridges.
Any closure is disruptive, but the Washington State Department of Transportation chose these dates to avoid the busy Memorial Day weekend. The work requires dry weather and may be rescheduled if it rains.
The extended closure will eliminate the need for 10 consecutive nights of ramp and intersection closures near the interchange and fewer traffic shifts, which improves safety for workers and people driving through the work zone. It also reduces the chances that opening the new interchange will be delayed.
During the closure, WSDOT contractor crews will install new drainage and electrical crossings, pave the new roadway and build concrete islands that will form a portion of the new I-90/SR 18 diverging diamond interchange. The work also includes constructing a left turn pocket for traffic from westbound SR 18 onto Southeast 104th Street and a signalized U-turn south of I-90 that will allow eastbound SR 18 traffic to head westbound toward Auburn.
The extended closure will allow both the left turn pocket from westbound SR 18 to Southeast 104th Street and the signalized U-turn to westbound SR 18 to open while work on the rest of the interchange is completed.
What to expect
Eastbound and westbound I-90 traffic will not be affected during the closure, but people traveling through the area should be aware that:
Vehicles will not be permitted on either direction of SR 18 beneath the I-90 bridges.
Traffic on the eastbound I-90 off-ramp will only be able to turn south onto westbound SR 18. No left turns onto eastbound SR 18/Snoqualmie Parkway will be allowed.
Traffic on the westbound I-90 off-ramp can only turn north onto Snoqualmie Parkway or continue onto the westbound I-90 on-ramp. No left turns onto westbound SR 18 will be allowed.
Eastbound SR 18 traffic must use the eastbound I-90 on-ramp and follow a detour.
Southbound traffic on Snoqualmie Parkway must use the westbound I-90 on-ramp and follow a detour.
Detour options
People can detour around the closure using eastbound and westbound I-90 and loop around at the Southeast North Bend Way (exit 27) interchange to the east of SR 18 and the Preston-Fall City (exit 22) or the High Point Way (exit 20) interchanges to the west of SR 18. Signs will indicate the detour route for travelers.
Westbound I-90 freight traffic should either loop back and take westbound SR 18 or continue on westbound I-90 to southbound I-405. Freight traffic should not use Issaquah city streets or Issaquah-Hobart Road, which are unsuitable for semi-trucks. Similarly, eastbound SR 18 freight traffic cannot use Issaquah city streets to access I-90.
All people traveling through the I-90/SR 18 interchange during the closure should expect delays and add time to their travel plans. Real-time traffic information is available on the WSDOT app, statewide travel map, and social media channels.
After the closure
When SR 18 reopens Wednesday, June 4, most of the construction on the southern end of the new interchange will be complete. Work remains under the I-90 bridges and on the project’s northern end before traffic can be shifted into the final diverging diamond configuration later this summer.
In addition to building the new interchange, the project is:
- Widening more than 2 miles of SR 18 south of I-90 to two lanes in each direction.
- Building new four-lane bridges over Lake and Deep creeks will allow fish and wildlife to pass beneath SR 18.
- Constructing a new two-lane bridge over Raging River next to the existing SR 18 bridge.
The full closure from May 29 to June 4 will be significant and unavoidable for anyone who travels through the I-90/SR 18 interchange. With no access in either direction under I-90, detour routes will be lengthy and delays are likely, especially during peak travel hours. Drivers, freight haulers, and local residents should plan well in advance, build in extra travel time, and stay alert to signage and detour instructions.
This is a major closure on a critical freight and commuter corridor, and failure to prepare could result in long delays and considerable inconvenience. WSDOT encourages all travelers to consult real-time traffic tools and avoid the area whenever possible during the shutdown.
[Information provided by the Washington State Department of Transportation]
