Weekend traffic headaches ahead: Major closures planned on I-405, SR 520/Montlake, and SR 99

Drivers traveling around the Puget Sound region this weekend should prepare for yet another weekend of delays as several major road projects overlap across King County.

The Washington State Department of Transportation (WSDOT) said travelers can expect congestion on key north-south routes, including I-405, I-5, and SR 99, along with impacts for those traveling between Seattle and the Eastside. Officials are urging people to allow extra travel time and check conditions before heading out.

Southbound I-405 closing between Bellevue and Renton

One of the biggest impacts this weekend will be a full closure of southbound I-405 between Bellevue and Renton.

Starting as early as 11:30 p.m. Friday, southbound I-405 will close between Coal Creek Parkway S.E. and N. 30th Street. The closure is scheduled to remain in place until 4 a.m. Monday.

Several ramps will also be closed, including:

• Coal Creek Parkway S.E. on-ramp to southbound I-405
• Lake Washington Boulevard on- and off-ramps (Exit 9)
• N.E. 44th Street on- and off-ramps (Exit 7)
• Southbound I-405 off-ramp to N.E. 30th Street (Exit 6)

According to WSDOT, crews will complete drainage work, repaving, and a traffic shift as part of the I-405/Renton to Bellevue Widening and Express Toll Lanes Project.

The official detour will direct drivers to use Coal Creek Parkway, Duvall Avenue, and Sunset Boulevard.

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Montlake Boulevard and SR 520 interchange closing for the weekend

The second weekend-long closure of the Montlake Boulevard and SR 520 interchange is also set to begin Friday night.

Montlake Boulevard will close in both directions between E. Hamlin Street and E. Louisa Street from 10 p.m. Friday until 6 a.m. Monday.

The following closures will be in effect:

• On-ramps from Montlake Boulevard to eastbound and westbound SR 520
• Eastbound SR 520 off-ramp to Montlake Boulevard
• A section of E. Roanoke Street west of Montlake Boulevard
• Lake Washington Boulevard between Montlake Boulevard and 24th Avenue E.

The westbound SR 520 off-ramp to northbound Montlake Boulevard will remain open.

WSDOT said crews are installing new sign structures on Montlake Boulevard. A path for people walking, biking, and rolling across SR 520 will remain available, although a limited detour south of SR 520 will be required.

Drivers headed toward the University District should expect heavy congestion. Detours include I-5 and Boyer Avenue.

Northbound SR 99 closing at First Avenue South Bridge

Drivers using SR 99 in Seattle will also encounter a weekend closure.

Northbound SR 99 will close at the First Avenue South Bridge from 5 a.m. Saturday until 11:59 p.m. Sunday for bridge and structure preservation work.

During the closure, travelers will not be able to:

• Continue northbound on SR 99 beyond the bridge
• Access E. Marginal Way from the bridge
• Access Michigan Street from the bridge

Additional closures include:

• The Occidental Avenue S./S. Kenyon Street connection to northbound SR 99
• The West Marginal Way S./S. Holden Street connection to northbound SR 99
• The First Avenue S. connection to northbound SR 509

Drivers can use the South Cloverdale Street exit and cross the Duwamish River using the 14th Avenue S. Bridge.

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Continued lane reductions on I-5

Adding to the congestion, northbound I-5 remains reduced to two lanes across the Ship Canal Bridge as part of the Revive I-5 Ship Canal Bridge Preservation project.

The lane reduction is expected to remain in place through the end of 2026. The northbound express lanes continue to operate 24 hours a day, and the Harvard Avenue on-ramp to northbound I-5 remains closed until mid-October.

What drivers should expect

While the projects are spread across the Seattle area, WSDOT says the combined impacts will be felt regionwide as drivers seek alternate routes.

With major closures affecting I-405, the SR 520/Montlake interchange, SR 99, and ongoing restrictions on I-5, officials recommend planning ahead, allowing extra travel time, and checking traffic conditions before leaving home.