WSDOT Closes Southbound I-405 Bellevue to Renton Aug 21 to 24

Drivers between Bellevue and Renton face another full southbound Interstate 405 shutdown over the Aug. 21 to 24 weekend, overlapping with Montlake Boulevard and State Route 99 bridge work that will squeeze Seattle corridors at the same time. The Washington State Department of Transportation set the package in an Aug. 17 news release, giving travelers a short window to reroute airport runs, hotel check-ins, and weekend road trips before the cones go up.

This is not a single-ramp repair. Southbound I-405 closes for most of the weekend, the SR 520 and Montlake interchange closes overnight into Monday morning, and northbound SR 99 at the First Avenue South Bridge closes Saturday into Sunday while northbound I-5 stays pinched to two lanes on the Ship Canal Bridge. KOMO News confirmed the same weekend stack on Tuesday morning, underscoring how quickly spillover can move onto local streets when those four corridors tighten together.

What WSDOT scheduled on southbound I-405

Southbound I-405 will close from Coal Creek Parkway Southeast to North 30th Street from 11:30 p.m. Friday, Aug. 21, until 4 a.m. Monday, Aug. 24. That stretch covers the core Bellevue-to-Renton commute and the usual backup for travelers heading from Eastside hotels toward Sea-Tac or south King County.

WSDOT lists closed ramps at Coal Creek Parkway Southeast onto southbound I-405, the Lake Washington Boulevard ramps at Exit 9, the Northeast 44th Street ramps at Exit 7, and the southbound off-ramp to Northeast 30th Street at Exit 6. Crews will handle drainage, repaving, and a traffic switch for the I-405 Renton to Bellevue Widening and Express Toll Lanes Project, with a signed southbound detour in place.

Anyone who used I-405 through Kirkland during the Aug. 14 to 17 Exit 18 ramp closure already saw how quickly Eastside traffic shifts onto parallel arterials. This newer package is farther south and lasts longer overnight into Monday, so Renton, Factoria, and Newcastle street grids will likely absorb more of the load.

Montlake Boulevard and the SR 520 interchange

In Seattle, Montlake Boulevard closes between East Hamlin Street and East Louisa Street from 10 p.m. Friday, Aug. 21, to 6 a.m. Monday, Aug. 24. The work installs new sign structures based on community design recommendations from 2024, according to WSDOT.

Closed pieces include Montlake Boulevard on-ramps to eastbound and westbound SR 520, the eastbound SR 520 off-ramp to Montlake Boulevard, a short section of East Roanoke Street west of Montlake, and Lake Washington Boulevard between Montlake Boulevard and 24th Avenue East. The westbound SR 520 off-ramp to northbound Montlake Boulevard stays open.

WSDOT says it will keep a path for people walking, biking, and rolling across SR 520 on Montlake Boulevard, with a limited detour south of the freeway. Travelers booking University of Washington visits, Husky Stadium events, or Cap Hill to Bellevue trips should treat Montlake as unavailable for that full weekend night-into-morning window.

Northbound SR 99 at the First Avenue South Bridge

Northbound SR 99 closes at the First Avenue South Bridge from 5 a.m. Saturday, Aug. 22, to 11:59 p.m. Sunday, Aug. 23, for bridge and structure preservation. During that closure, drivers cannot reach East Marginal Way or Michigan Street from the bridge or continue north on SR 99.

Additional closures hit the Occidental Avenue South and South Kenyon Street connection to northbound SR 99, the West Marginal Way South and South Holden Street connection to northbound SR 99, and the First Avenue South link to northbound SR 509. This is a new weekend window after the earlier Aug. 15 to 16 First Avenue South Bridge closure, so south Seattle and SODO freight and airport-adjacent trips need a fresh Saturday and Sunday plan.

KOMO noted that two lanes of the northbound bridge were already constrained earlier this year after deck issues, which helps explain why preservation work keeps returning to this span. Do not assume a mid-day reopen on either Saturday or Sunday unless WSDOT posts one.

Ship Canal Bridge pressure that does not pause

Northbound I-5 across the Ship Canal Bridge remains reduced to two lanes through the end of 2026 under the Revive I-5 Ship Canal Bridge Preservation project. Express lanes stay northbound-only around the clock, and the Harvard Avenue on-ramp to northbound I-5 remains closed until mid-October.

That ongoing pinch matters because the weekend package forces more traffic onto I-5 and city streets at the same time Montlake and SR 99 are disrupted. A traveler flying into Sea-Tac and driving north to a Capitol Hill hotel, or leaving downtown for an Eastside brunch, can hit more than one of these constraints on a single trip.

If your weekend plan includes outdoor stops after the highway grind, the evergreen Seattle things to do guide is a practical place to cluster neighborhoods that stay reachable without a southbound I-405 hop. Road-trip guests linking Seattle to mountain parks can also sanity-check timing against the Mount Rainier to Olympic route overview before locking Saturday departures.

How this weekend differs from the last two packages

WSDOT has stacked several Puget Sound construction weekends in August, but the traveler decision here is specific. The Kirkland Exit 18 package was a northern I-405 interchange shutdown. The mid-August SR 99 bridge work covered an earlier First Avenue South window. This release combines a long southbound Bellevue-to-Renton I-405 closure with Montlake and another SR 99 bridge outage.

Confirmed fact from WSDOT: the I-405 southbound and Montlake windows both run Friday night into Monday morning, while the SR 99 bridge outage is the Saturday-Sunday core. Interpretation: overlapping north-south and east-west closures raise the chance of diverting traffic into unfamiliar neighborhoods even for locals.

Unknown until crews report in: whether rain forces a postponement. WSDOT says much of the work needs fair weather and may move if storms arrive, with updates on the Travel Center map, the WSDOT app, and King County email alerts.

The practical move for most visitors is simple: rebuild the weekend itinerary around the closed segments instead of hoping for a short delay. Families heading between Seattle neighborhoods and Eastside lodging should decide by Friday whether to stay west of Lake Washington, stay east, or accept a much longer cross-lake drive.