All traffic heading to the Eastside from Seattle on Interstate 90 after 11:30 p.m. Friday and 11:59 p.m. Saturday (April 20-22) will be diverted overnight to the center roadway express lane, beginning west of the Mount Baker Tunnel, across Mercer Island. Mainline eastbound I-90 will reopen to traffic at 7 a.m. on Saturday and 8 a.m. Sunday.

The traffic diversion is necessary because the Washington State Department of Transportation will close the eastbound I-90 tunnels in Seattle and Mercer Island to test new technology for improved smoke and fire detection and response inside the tunnels.

Eastbound I-90 traffic diversion April 20-22

11:30 p.m. Friday to 7 a.m. Saturday

11:59 p.m. Saturday to 8 a.m. Sunday

Access to Mercer Island eastbound from the I-90 Express Lanes is available at 77th Avenue Southeast and Island Crest Way.

A flammable cargo restriction will be in place on both directions of I-90 through all Mount Baker and Mercer Island tunnels Friday and Saturday nights.

Flammable cargo restrictions on I-90 April 20-22

10 p.m. Friday to 8 a.m. Saturday

11 p.m. Saturday to 8 a.m. Sunday

WSDOT contractor crews will set small, controlled fires in the tunnels to test a new video-detection system. Testing will be in the Mercer Island Lid tunnel Friday night and in the Mount Baker Tunnel Saturday night. Most of the controlled fires will be set in the Mount Baker Tunnel. The small fires, set in metal pans 2-8 feet long, should not be visible to traffic, but some smoke might be seen escaping tunnel ventilation shafts during the tests.