Seattle SR 99 First Avenue South Bridge Closes Aug 15 to 16

Northbound State Route 99 will close at Seattle’s First Avenue South Bridge from 5:00 a.m. Saturday, August 15, through 11:59 p.m. Sunday, August 16, 2026, for bridge and structure preservation work, according to the Washington State Department of Transportation.

Drivers heading to Sea-Tac, downtown Seattle, or the waterfront from the south should detour before the weekend window starts and recheck live WSDOT conditions, because the First Avenue South Bridge is a core northbound SR 99 link into the city.

What WSDOT scheduled for the First Avenue South Bridge

In its August 2026 Puget Sound weekend construction release, WSDOT says northbound SR 99 will close at the First Avenue South Bridge from 5:00 a.m. Saturday, August 15, to 11:59 p.m. Sunday, August 16, for bridge and structure preservation.

During that window, travelers will not be able to access East Marginal Way or Michigan Street from the First Avenue South Bridge or continue northbound on SR 99. That is a multi-hour, multi-day cut on a major northbound approach, not a short overnight lane drop.

WSDOT also lists additional closures tied to the same northbound package: 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 connection to northbound SR 509. Those feeders matter if your usual GPS route jumps between local streets and the highway.

Local traffic reporting, including Fox 13 Seattle’s weekend road-closure roundup, has been amplifying the same Puget Sound construction cluster for drivers who only see alerts in the car on Saturday morning.

The Friday night tunnel window is separate but related

WSDOT says the SR 99 tunnel will close in both directions overnight from 10:00 p.m. Friday, August 14, to 6:00 a.m. Saturday, August 15, for routine tunnel maintenance. That is the night before the longer First Avenue South Bridge closure starts.

If you land at Sea-Tac late Friday and drive north, treat the tunnel overnight as its own decision. A late Friday arrival can force a detour even before the Saturday bridge cut begins. Recheck the tunnel status before you leave the airport curb rather than assuming SR 99 is open because the longer bridge notice starts at 5:00 a.m.

The weekend package is also stacked on other active Seattle work. WSDOT notes northbound I-5 remains reduced to two lanes across the Ship Canal Bridge until the end of 2026, with express lanes northbound only and the Harvard Avenue on-ramp closed until mid-October. That means a SR 99 problem can push more cars onto an already constrained I-5 corridor.

Weather can still move the schedule. WSDOT says much of the work needs good weather and may be rescheduled for rain. Schedule updates post on the Travel Center map, the WSDOT mobile app, and King County email alerts.

How this hits Sea-Tac and downtown trips

Sea-Tac airport trips that normally climb northbound on SR 99 toward downtown hotels, cruise terminals, or King Street Station need a new plan for Saturday and Sunday. Build extra time for I-5, local arterials, and rideshare surge pricing when a highway link is dark.

Cruise and hotel guests staying south of downtown who planned a quick SR 99 hop into the core should leave earlier for embarkation morning. The First Avenue South Bridge is not a minor side street. When it is closed northbound, downtown arrivals from the industrial south stretch can cascade into late check-ins and missed shore excursions if you cut the buffer too thin.

Deep Arrival’s things to do in Seattle list is still useful for trip planning after you clear the highway problem. It does not replace a live detour map. Use it for neighborhood timing only once you know how long the road portion will take.

Transit remains the cleanest alternative for some city trips. WSDOT explicitly asks people to use transit and park-and-ride options when major weekend packages land. If your destination is downtown and you already hold a Link light rail option from the airport corridor, compare door-to-door time before you fight the detour in a rental car.

What to do Friday night through Sunday night

Before you leave home or the airport, open the WSDOT Travel Center and confirm whether the First Avenue South Bridge and SR 99 tunnel are still on the published clocks. Screenshots of the notice help if a navigation app keeps pushing you onto a closed ramp.

For Saturday and Sunday northbound trips, assume the bridge is closed for the full advertised span unless WSDOT posts an early reopen. Do not treat a short gap in traffic cones as permission to ignore the order. Follow posted detour signs and crew directions in the work zone.

If you are driving a one-way airport drop-off, build a return path that does not depend on the closed northbound link. Southbound options can also clog when everyone dumps onto the same alternate. Expect delays in new places and at new times, which is exactly how WSDOT describes this weekend’s regionwide construction pattern.

Commercial drivers and shuttle operators should brief passengers early. A 20-minute hotel transfer can become an hour when the bridge and tunnel windows stack with I-5 reductions.

This is a dated weekend operations story with primary proof from WSDOT and same-day local amplification. Treat the First Avenue South Bridge and tunnel clocks as hard planning inputs for Seattle travel through Sunday night, then recheck before the next work week begins.