*Editor’s Note: WSDOT frequently reschedules work due to weather and other factors. Be sure to check back with Living Snoqualmie for updates between now and the scheduled start date of May 15.
Both directions of State Route 18 will close around the clock for more than five days beginning Thursday night, May 15, 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 15, through 5 a.m. Wednesday, May 21, traffic will not be allowed on either direction of SR 18 beneath the I-90 bridges.
Any closure is disruptive, but the Washington State Department of Transportation chose these dates to avoid busy travel weekends on Mother’s Day (May 11) and Memorial Day (May 26). 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 is 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 turning 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 will only be able to 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 Preston-Fall City (exit 22) and Southeast North Bend Way (exit 27) interchanges.
Westbound I-90 freight traffic should use either the Preston-Fall City exit to 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 not suitable 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 and WSDOT’s statewide travel map and social media channels.
Before the big closure
WSDOT will reduce SR 18 to a single lane with flaggers, police officers, and a pilot vehicle alternating eastbound and westbound traffic from 9 p.m. Saturday, May 3, to 5 a.m. Sunday, May 4. The lane reduction will stretch from beneath the I-90 bridges to approximately Southeast 104th Street.
They’ll move barricades and restripe the roadway, shifting both lanes of SR 18 to the west to create a safe work area for crews to continue work on the diverging diamond interchange. If you’re driving through the area Saturday night, watch for signs, follow instructions from the flaggers and police officers, and expect delays.
After the closure
When SR 18 reopens Wednesday, May 21, 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 northern end of the project 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 that 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.
SR 18 widening is expected to finish later this year.
