Coal Creek sewer upgrade

Project update

July 2026

Tunneling begins soon!

Tunneling for the Coal Creek Sewer Upgrade Project will begin at the Red Cedar Trailhead as early as Monday, July 20. The tunneling machine will run 24/7 to ensure smooth and safe operation. About one mile of the new sewer pipe will be installed by tunneling underground.

What to expect during tunneling:

• Work activity at the Red Cedar Trailhead will continue around the clock during tunneling. The tunneling machine will operate 24/7.
• The tunneling machine will dig deep underground. You may feel small vibrations. King County will monitor tunneling progress to ensure work continues safely.
• There will be construction noise typical to a work site during daytime work hours. The contractor will follow the after-hours permit requirements approved by the City of Bellevue.
• Traffic impacts will include a northbound lane closure on Coal Creek Parkway SE near the Red Cedar Trailhead. The single lane closure will be in effect from 10:30 am to 5:00 am, 7 days a week. This lane closure will not be in effect between 5:00 am and 10:30 am to help reduce morning commute impacts.
• Tunneling is expected to be completed by early 2027.
• The Red Cedar Trailhead is closed. Trail users can access the natural area via the Forest Drive, Red Town, Cinder mine, and other trailheads. Please follow trail detours and stay out of fenced construction areas.

Construction monitoring devices during tunneling

Several construction monitoring devices have been installed in right-of-way areas along the tunneling route. These devices collect data about underground conditions to track tunnelling progress. They will remain in place until tunneling is complete.

Please do not disturb the construction monitoring devices. Contact our team with any questions about the devices.

An example of a construction monitoring device

Traffic impacts on Coal Creek Parkway SE

Commuters on Coal Creek Parkway SE can expect ongoing single lane closures and traffic delays between the Red Cedar Trailhead and I-405. Flaggers will be present to direct traffic. Drivers and cyclists will share a lane when traveling through the work area and are advised to use caution.

Southbound lane closures on Coal Creek Parkway SE are permitted for weekdays, 6:00 am to 3:00 pm. A northbound lane closure near the Factoria Boulevard SE intersection is permitted for weekdays from 10:30 am to 7:30 pm.

During 24/7 tunneling, northbound traffic impacts will include a lane closure on Coal Creek Parkway SE near the Red Cedar Trailhead. This single lane closure will be in effect from 10:30 am to 5:00 am, 7 days a week. It will not be in effect between 5:00 am and 10:30 am to help reduce morning commute impacts.

Reminder: do not enter construction zones

The Red Cedar trailhead and other work areas are active construction zones and remain closed to all public use. Other trailheads in the area such as the Cinder Mine, Red Town, Coal Creek Family YMCA, and Forest Drive trailheads are available for trail users. Stay out of fenced areas and the creek bank for your safety and to protect the Coal Creek Natural Area and salmon habitat.

Stay in touch!

Sign up for the project email list to get updates, learn about construction, and find outreach activities that you can participate in!

Call or email our construction hotline at 425-537-7195 or CoalCreekProject@kingcounty.gov.