The Interstate 90 and State Route 18 diverging diamond interchange and widening project south of Snoqualmie is nearly complete. Contractor crews working for the Washington State Department of Transportation are planning at least three extended weekend closures for final paving and striping work.
This work is dependent on the weather. Weather permitting, the first closure will take place overnight on March 31 to set up equipment and barriers, with paving to start the evening of April 2. At least one lane will reopen between weekend closures.
Directional and full closures
There will be two directional closures, one for each direction of SR 18 between I-90 and Issaquah-Hobart Road and a third full closure of SR 18 under I-90 at the I-90/SR 18 interchange.
These closures will begin with an overnight closure of eastbound SR 18 at 8 p.m. Tuesday, March 31, to set up traffic control and remove barriers. Eastbound SR 18 will reopen at 5 a.m. Wednesday morning, April 1, with the right lane closed so crews can begin to remove 8,500 feet of guardrail before paving work begins as early as 9 p.m. Thursday, April 2. At least one lane of SR 18 will reopen at 5 a.m. Monday, April 6, while crews continue to reinstall the guardrail.
What to expect
Closures for paving and striping depend on relatively warm, dry weather. Project engineers will watch the weather closely when determining the precise dates for these closures. This also means that planned closures may be postponed or rescheduled on short notice if precipitation or cold temperatures are forecast.
Each of the three extended weekend closures will begin at 9 p.m. Thursday, the roadway will reopen with at least one lane at 5 a.m. Monday morning. There will be around-the-clock single-lane closures in the days leading up to and after each of these three SR 18 closures to allow crews to prepare the roadway for paving and to work on drainage after paving.
When crews finish paving SR 18, there will be an additional weekend-long closure to apply final striping to the highway and ramps. This will consist of a sequence of full directional closures and ramp closures, each lasting up to 8 hours, not occurring simultaneously.
Detour options
Drivers should follow all signed detours or use alternate routes during these closures and expect significant delays and traffic congestion in the area and near the SR 18 and I-90 interchange.
Freight haulers and truck drivers should avoid Issaquah-Hobart Road and Issaquah city streets, which are not suitable for freight traffic. Truck traffic should use SR 169, I-405, and/or I-90 for all detours.
All people traveling through the I-90/SR 18 interchange during these closures 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.
After the closure
When SR 18 reopens after paving and striping are complete, the diverging diamond interchange project should be complete. SR 18 widening is expected to be completed in late summer this year.
Work on this project began in 2023 to install three new bridges, reconfigure the I-90/SR 18 interchange to a diverging diamond and widen over 2 miles of SR 18 from two to four lanes. Other project improvements include new traffic cameras for SR 18 and I-90, as well as safety, stormwater, fish passage, and habitat enhancements along this busy corridor.
[Information provided by the Washington State Department of Transportation]
