Summary:

Seattle drivers should prepare for significant roadwork on I-5 and SR 99 from August 15th to late August, which will result in full freeway closures, overnight detours, and lane reductions. The most significant disruption will be the closure of all northbound I-5 lanes between I-90 and NE 45th Street from August 15th to 18th, while work will also be done on the SR 99 tunnel and a newly paved stretch of SR 99 in South King County. Drivers are advised to plan ahead and expect delays.

Seattle drivers should brace for a busy stretch of roadwork beginning Friday, Aug. 15, and continuing through late August as WSDOT crews tackle several major projects on I-5 and SR 99. The work will bring full freeway closures, overnight detours, and lane reductions across the city and South King County.

The most significant disruption begins late Aug. 15, when all mainline northbound I-5 lanes between I-90 and NE 45th Street will close for the weekend. Crews will finish repairs on the Ship Canal Bridge and restore the freeway to four lanes. The closure begins at 11:59 p.m. Friday and ends by 5 a.m. Monday, Aug. 18.

During the closure, drivers will need to use the I-5 express lanes, which will remain northbound around the clock. The Cherry/Columbia ramp, typically reserved for HOV traffic, will open to all vehicles from early Saturday morning until early Monday.

Downtown-bound drivers from the south will need to exit before the express lanes, as there are no downtown exits from that route. Alternate options include Edgar Martinez Drive or the Dearborn, James, or Madison Street exits. Travelers can also take eastbound I-90 to Rainier Avenue.

Ramp closures to northbound I-5 will begin Friday evening, starting at 9 p.m. for Dearborn, Cherry, and University streets; 10 p.m. for westbound I-90, Olive Way, Mercer Street, and westbound SR 520 to Roanoke Street; and 11 p.m. for eastbound I-90, westbound SR 520, and Harvard Avenue East.

Just days later, WSDOT will turn its attention to the SR 99 tunnel, where traffic lanes have worn smooth since it opened in 2019. Starting Monday night, Aug. 18, crews will begin “shot-blasting” the pavement — a high-velocity resurfacing technique — to improve traction.

The work will require up to five overnight closures in each direction, beginning with northbound lanes from 11 p.m. to 4:30 a.m. nightly. The Colorado Avenue South on-ramp to northbound SR 99 will close an hour earlier at 10 p.m. Once the northbound work is complete, crews will repeat the process in the southbound lanes.

In South King County, lane striping begins Saturday night, Aug. 16, on a newly paved two-mile stretch of SR 99 between South 200th Street in SeaTac and SR 516 in Des Moines. Double-lane closures in both directions will occur nightly from 9 p.m. to 5 a.m. for about three weeks, with at least one lane open in most areas.

Two major overnight closures are also planned: northbound SR 99 between South 216th and South 208th streets on Tuesday, Aug. 19, and both directions of SR 516 at the SR 99 intersection from Saturday, Aug. 23, through Monday, Aug. 25.

WSDOT urges drivers to plan ahead, expect delays, and allow extra time as crews work to improve safety and keep traffic moving across the region.