Northbound drivers on State Route 99 are about to hit a hard stop. All northbound lanes of the First Avenue South bridge in Seattle will be closed to vehicles for three days starting Monday, March 9, so crews can carry out emergency stabilization after an inspection found cracked steel deck grates. The shutdown runs from 5 a.m. on March 9 through 8 p.m. on March 11 and will give crews time to weld, reinforce and install temporary steel plates on the grated deck. Once the daytime repairs wrap up, northbound traffic will be allowed again at a reduced speed to protect the temporary plates, and drivers should brace for detours and heavier congestion across the area while the work is underway.
In a news release, the Washington State Department of Transportation said the work is Phase 1 of a three-part plan and will let crews "modify existing grated panels and install steel plates" over the cracked sections. According to WSDOT, the temporary repairs will allow all northbound lanes to reopen with a temporary 25 mph speed limit and will be followed by limited panel replacements in mid-to-late April. Longer-term design work is already underway for a full northbound deck replacement expected in 2027.
Inspection Raised Red Flags
The trouble started when two right lanes were pulled from service after a routine inspection on Feb. 18 identified cracks in the steel deck grates, and officials quickly cut the posted speed to 25 mph as a precaution. KIRO 7 reports that WSDOT engineers returned to the bridge for a detailed assessment and warned commuters to expect delays. Local coverage at FOX 13 Seattle summarizes the agency timeline and says another full northbound closure is expected in April to replace the worst panels.
Drivers Should Plan Ahead
WSDOT is urging drivers to use alternate routes such as I-5 and I-405 during the March 9-11 work and warned that the bridge repairs are being sequenced around other regional closures. The short window for the First Avenue South work follows full-weekend I-405 closures in Bothell the weekends of March 7-9 and March 13-16, which WSDOT says will limit detour capacity and likely increase backups on connecting corridors. Travelers are encouraged to allow extra time, consider transit or carpooling and check real-time maps before heading into the city.
What’s Next And Why It Matters
WSDOT says it will manufacture nine new steel grate panels and expects to begin their replacement in mid-to-late April, with installation expected to take roughly six weeks once the panels arrive. Completing that panel work before the 2026 FIFA World Cup in June is a stated agency goal to keep SR-99 available during a busy travel season, and design work for a full northbound deck replacement is planned for 2027. For now, the temporary plates and reduced speed are intended to reduce stress on the central span until longer repairs can be completed.
To stay informed, travelers can follow local traffic reporting along with WSDOT travel alerts and maps for real-time updates and closure details. Agencies recommend off-peak travel, transit or flexible schedules while this work is underway to avoid the worst of the backups.
