WSDOT to close SR 99 tunnel overnight for $1.5M road grip project
Aug 18, 2025, 6:27 AM
Cars exiting the SR 99 tunnel in downtown Seattle. (Photo courtesy of WSDOT)
(Photo courtesy of WSDOT)
In their own words, the Washington State Department of Transportation (WSDOT) said, “It’s about time for people who use the State Route 99 (SR 99) tunnel under downtown Seattle to get a grip.”
Grip as in better traction through the downtown tunnel.
Since opening in February 2019, the surface of the two-mile tunnel has worn down due to the 47,000 daily commuters, and WSDOT plans to add texture to the pavement. The $1.5 million project will restore the tire grip to its original form, as it was when the road opened more than six years ago.
A technique called shot-blasting will add traction through high-velocity particle grains. Trucks will tow machines that blast the grains and vacuum any dust created during the process, ensuring that the tunnels’ air filtration systems and storm drains do not clog.
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Work begins Monday night
Work begins with the closure of all northbound SR 99 lanes on Monday night, August 18. From 11 p.m. to 4:30 a.m. nightly for up to five nights, all northbound SR 99 traffic will need to exit onto S. Dearborn Street. The Colorado Avenue S. on-ramp to northbound SR 99 will close an hour earlier each night at 10 p.m.
Once crews finish texturing northbound lanes, they will switch and close the southbound tunnel for up to five nights. From 10 p.m. to 5 a.m. nightly, all southbound SR 99 traffic must exit at the Denny Way off-ramp. The Sixth Avenue S. on-ramp to southbound SR 99 will close at the same time.
On game nights, closures will not begin until two hours after the last pitch for Seattle Mariners games at T-Mobile Park or the completion of Seattle Reign and Sounders games at Lumen Field.
Detours will direct drivers to city surface streets, or they can opt to travel on Interstate 5 (I-5) during these overnight closures. This entire shot-blasting project should wrap up by Labor Day Weekend.
Nate Connors is a traffic reporter for KIRO Newsradio. Follow him on X. Read more of his stories here. Submit news tips here.
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