Major 5-day closure underway on SR 18 at I-90 in Snoqualmie, WA

State Route 18 is closed in both directions near Interstate 90 for more than five days, beginning Thursday, May 29, to facilitate the construction of a new diverging diamond interchange.

Timeline:

The closure is scheduled from 9 p.m. Thursday, May 29, to 5 a.m. Wednesday, June 4.

The Washington State Department of Transportation (WSDOT) said the extended closure will allow crews to complete a significant portion of the I-90/SR 18 Interchange Improvements project.

An aerial view of construction at the SR 18 interchange with I-90 near Snoqualmie, WA. (WSDOT)

Travelers should plan for detours and anticipate extended travel times. Keep reading for what you need to know about the closure.

SR-18 closure details

Timeline:

Drivers who were planning to use SR-18 at Snoqualmie will need to make alternative plans due to the upcoming closure.

  • When: 9 p.m. Thursday, May 29, to 5 a.m. Wednesday, June 4.
  • Where: Both directions of SR 18 beneath the I-90 bridges.
  • Purpose: Installation of new drainage and electrical crossings, roadway paving, and construction of concrete islands for the new diverging diamond interchange. This work also includes building a left turn pocket for westbound SR 18 to Southeast 104th Street and a signalized U-turn south of I-90 for eastbound SR 18 traffic heading westbound toward Auburn.
diverging diamond interchange illustration

A diverging diamond interchange will improve traffic flow at one of Washington's busiest interchanges. (WSDOT)

Big picture view:

WSDOT chose these dates to avoid the busy Memorial Day weekend. The work is weather-dependent and may be rescheduled if it rains. 

This extended closure is expected to eliminate the need for 10 consecutive nights of ramp and intersection closures, improving safety for both workers and drivers and reducing potential project delays.

What detours will be available during the SR-18 closure?

Drivers can detour around the closure using eastbound and westbound I-90. Detour routes will be indicated by signs.

East of SR 18

Loop around at the Southeast North Bend Way (exit 27) interchange.

West of SR 18

Loop around at the Preston-Fall City (exit 22) or High Point Way (exit 20) interchanges.

"You can detour using eastbound and westbound I-90 and loop around at nearby interchanges – exit 20 (High Point Way) or exit 22 (Preston-Fall City) to the west of SR 18 or exit 27 (Southeast North Bend Way) east of SR 18 – to reach your destination."

"Westbound I-90 freight traffic should either use exit 22 (Preston-Fall City) to loop back to SR 18 or continue on westbound I-90 to to southbound I-405. Issaquah city streets and Issaquah-Hobart Road are not suitable for semi-trucks." -WSDOT

What should drivers expect during the SR-18 closure?

While eastbound and westbound I-90 traffic will not be directly affected, drivers navigating the interchange area should be aware of the following restrictions:

  • No vehicles will 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. Left turns onto eastbound SR 18/Snoqualmie Parkway will not 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. Left turns onto westbound SR 18 will not 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.

Important note for freight traffic

Westbound I-90 freight traffic

Freight drivers should either loop back and take westbound SR 18 or continue on westbound I-90 to southbound I-405. Freight traffic should avoid Issaquah city streets or Issaquah-Hobart Road, as these are not suitable for semi-trucks.

Eastbound SR 18 freight traffic

Freight drivers can not use Issaquah city streets to access I-90.

All drivers traveling through the I-90/SR 18 interchange during the closure should expect delays and adjust their travel times accordingly.

What to know after the SR-18 closure

What's next:

Most of the construction on the southern end of the new interchange will be complete when SR 18 reopens on June 4. However, work will continue under the I-90 bridges and on the northern end of the project. Eventually, traffic will be shifted into the final diverging diamond configuration later this summer.

The project also includes:

  • Widening over 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 to allow for fish and wildlife passage.
  • Constructing a new two-lane bridge over the Raging River next to the existing SR 18 bridge.

The Source: Information in this story came from the Washington State Department of Transportation (WSDOT).

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