The northbound 1st Avenue South Bridge (SR 99) is facing a major, multi‑phase repair plan, and the first big closure is happening March 9–11, 2026. This is the result of cracks discovered in the steel deck grates during a February 18 inspection. Multiple outlets and WSDOT itself have now confirmed the timeline and scope.

What’s happening now

WSDOT will close all northbound lanes of the 1st Ave S Bridge for three days:

• Starts: Monday, March 9, 2026 at 5 a.m.

• Ends: Wednesday, March 11, 2026 at 8 p.m.

This closure allows crews to install temporary steel plates to stabilize cracked deck grates. Two lanes have already been closed since Feb. 18 for safety.

Why the closure is necessary

Inspectors found cracks in the steel deck grates on the northbound drawspan.

• WSDOT immediately shut down the two affected lanes.

• Further inspection showed the damage was significant enough to require staged repairs.

The full repair plan (3 phases)

WSDOT has laid out a year‑long, three‑phase approach:

Phase 1 — March 9–11, 2026

• Full northbound closure

• Temporary steel plates installed

• All lanes reopen afterward at reduced speed (25 mph)

Phase 2 — Mid to late April 2026

• Another closure (dates TBD)

• Replacement of the nine worst steel grate panels

Phase 3 — 2027

• Full deck replacement of the northbound span

• Expected to require longer closures

What drivers should expect

• Heavy congestion on West Seattle Bridge, South Park Bridge, and 5th Ave S detours

• Reduced speeds (25 mph) even after reopening

• Additional closures in April and again in 2027

For West Seattle and South Park travelers

This is the same corridor you rely on for Harbor Ave, West Marginal, and the Duwamish crossings. The three‑day closure will push a lot of traffic onto the South Park Bridge and 1st Ave S ramps, so expect backups similar to the West Seattle Bridge closure era, but shorter.