Two lanes on the northbound SR 99 First Avenue South Bridge over the Duwamish River are closed until further notice after an inspection identified concerns with the bridge’s steel grid deck, the Washington State Department of Transportation said.

WSDOT announced the lane closures following a bridge inspection conducted Wednesday, Feb. 18, and said the speed limit on the bridge has been reduced to 25 mph out of an abundance of caution to limit additional stress on the deck.

The bridge remains open and operational, including for maritime traffic, and vessel openings will continue as needed, according to WSDOT. The agency also opened the HOV lane to all traffic temporarily to help improve traffic flow, and drivers can still exit at Michigan Street.

Bridge engineers returned to the site Thursday, Feb. 19, to conduct a more detailed assessment. WSDOT said it is too early to outline a repair plan or timeline but expects to release a preliminary report and provide updates as repair plans are developed, with an anticipated public update by Friday, March 6.

Travelers through the corridor, including commuters from South King County cities such as Burien, SeaTac, Tukwila, Des Moines, Kent and Auburn, should expect ongoing delays, longer travel times and less predictable traffic conditions, especially during peak hours.

WSDOT noted the lane closures come on top of existing northbound Interstate 5 lane reductions related to the Revive I-5 program to preserve the Ship Canal Bridge, which could add pressure to the regional transportation system.

The agency is coordinating with the Seattle Department of Transportation and transit partners to monitor traffic conditions and manage impacts where possible, and is encouraging travelers to plan ahead, allow extra travel time, consider alternate routes and check the WSDOT mobile app or real time travel map for current conditions.

According to WSDOT, the First Avenue South Bridge is a movable double leaf bascule bridge that allows marine traffic to pass along the Duwamish River. The northbound span was originally built in 1956 and rebuilt in 1998, and carries about 48,000 vehicles per day. During its most recent inspection in 2024, the bridge was rated in fair condition.

WSDOT said the lane reduction underscores the ongoing need for preservation and targeted maintenance across the transportation system, noting that past work included a 2020 project to replace 14 select deck panels.