After months of procrastination and dread, Seattle’s main traffic event of 2025 is finally upon us — a full 30 days of northbound lane closures at the Interstate 5 Ship Canal Bridge for a necessary concrete repave.

Workers will restore a 900-foot-long section this summer as the first stage of a project that will close lanes on-again, off-again until 2027.

First, 4 miles of the entire northbound freeway will close this weekend, from the I-90 junction to Northeast 45th Street, from 11:59 p.m. Friday, July 18, until 5 a.m. Monday, July 21. Workers will install concrete safety barriers and stage heavy equipment. The I-5 express lanes will point northbound for drivers to bypass downtown.

Then beginning early Monday, the two left lanes of northbound I-5 will stay closed from approximately the Highway 520 junction to Northeast 45th Street, until the night of Aug. 15. Only two lanes will cross the canal. The express lanes will flow north throughout construction, which means southbound drivers can expect morning traffic jams.

Another full northbound closure is needed the weekend of Aug. 16-17, when contractors will remove the barriers and machines.

The Ship Canal Bridge, where the Washington State Department of Transportation performed more than 200 urgent pothole repairs in the past five years, became a symbol of regional and national underinvestment in maintenance. The bridge opened to traffic in 1962 and hasn’t been resurfaced since the 1980s.

WSDOT counts show 240,000 daily trips over the bridge, while city officials estimated that closing two lanes would divert 84,000 vehicles per day, or prevent those trips altogether. Thousands more will be delayed by cascading congestion.

I think it’s going to be kind of tough. People need to plan ahead and think about where they want to go and how they get there,” said Alex Hudson, executive director at Commute Seattle.

“The Ship Canal Bridge is one of the most important pieces of transportation infrastructure in the Pacific Rim, and making sure that we can keep it safe and extend the usable life is really important,” she said.

The last time WSDOT undertook a comparable I-5 project was August 2007, when contractors closed three northbound lanes in Sodo for two weeks building new expansion joints and pavement, a week less than scheduled.

The schedule

Look up at the Ship Canal Bridge and you’ll see huge sheets of steel, resembling a giant bamboo beach mat, beneath the entire upper and lower roadway decks as a safeguard in case concrete fragments trickle down.

For now, contractor Atkinson Construction will refurbish only a 900-foot starter section.

WSDOT’s plan subjects the public to ample punishment this summer,to rebuild only 10% of the northbound bridge surface.

That piece is a prelude to restoring two lanes along the entire northbound bridge early next year. WSDOT will open all lanes while six FIFA World Cup soccer matches draw visitors and a global spotlight to Seattle, from June 15 to July 6, before resuming repaves.

The agency says the starter section this year gives builders a four-week head start for early 2026, boosting the odds they can finish that portion before the World Cup, spokesperson Tom Pearce said.

The second reason is to answer a key question: How much has the 6½-inch-thick deck loosened, or maybe corroded, beneath its scarred 1½-inch surface?

If loose concrete extends down to the rebar, Atkinson will have to hammer out and rebuild certain areas, which takes longer than simply applying a new topcoat of synthetic concrete.

Widespread rot would force a longer schedule in future phases.

WSDOT quick-response teams have encountered sporadic 1- to 2-inch diameter holes through the deck, Pearce said.

Schedule risks were one reason, along with tight cash flow from the Legislature, that WSDOT Secretary Julie Meredith decided in January to cancel a March 1 start this year, renegotiate the $203 million construction contract, and defer a surface rehab south of the bridge.

This summer’s closures were timed after a series of I-405 closures (to build a triple-deck interchange in Kirkland and new toll lanes in Renton) and Sound Transit’s downtown Seattle station closures (to finish signals for the future Eastside connection and replace broken Westlake Station rails). The dates provide a cushion, so if I-5 work takes longer, it might still wrap up before Labor Day.

Drivers this weekend, and in the mid-August transition weekend, must either exit at I-90, at Edgar Martinez Drive, to the auxiliary lanes into James or Madison streets, or bypass downtown using the express lanes.

Why close all 4 miles, instead of letting drivers use more exits, including Highway 520? WSDOT’s answer is that diverting drivers at exits further south provides more detour options, and is therefore safer. “We could create gridlock, if say, we forced everybody off at Mercer,” added Pearce.

During the four-week lane reductions, the left-side Mercer Street entrance to northbound I-5 will remain open, as will access from Highway 520 to northbound I-5.,

The remaining two I-5 mainline lanes will operate at a temporary 50 mph speed limit, and will be only 10.5 feet wide rather than a standard 12 feet.

Squeezing together

Travelers who leave their car at home will find a normal supply of public transit.

“The buses and trains, they are busier than they were last year, and there’s still room on board,” Commute Seattle’s Hudson observed.

Sound Transit’s 1 Line carried an average 109,300 daily passengers in June, a 32% boost since 2019, buoyed by seven more stations. King County Metro ridership is rebounding, but below historic peaks.

Sound Transit will operate light rail trains every 10 minutes most hours, with no plans for supplemental trains. Sounder commuter trains often are added for weekend sports events.

Highway 99 tunnel tolls will continue, ranging from $1.25 to $2.80 based on time of day for Good to Go pass-holders, and a $2 pay-by-mail surcharge for cars without a pass.

Seattle converted its Aurora Avenue bus lanes to ban parking 24/7 instead of just in peak commute hours, which may speed the busy E Line buses past weekend traffic spillovers.

Seattle DOT says it will adjust signal timing and respond to incidents through its traffic operations center, with coordination to increase next year.

Just like the contractors’ education on the bridge, the four-week starter project will instruct officials about whether Seattle travel is resilient.

“How does reduction in capacity affect congestion on our surface arterials, that are our most dangerous roads, and do we see safety incidents as a result? Hudson wonders.

Recent performance on I-405, where traffic congealed as far as 5 miles during planned closures, wasn’t encouraging. WSDOT expects I-405 to clog when regional drivers bypass I-5 over the next few weeks.

Commute Seattle is educating its clientele of companies and agencies that employ roughly 300,000 workers. It will provide a public travel-aid hotline starting Thursday, at 206-613-3132.

The city of Seattle is giving $25 in transit fare to people who change at least one downtown car trip per week to other modes. Apply at flipyourtrip.org.

Hudson offers a parting reason for hope. Sometime in the first half of 2026, light rail capacity will double between downtown and Lynnwood, with trains arriving every five minutes, assuming Sound Transit can run its 2 Line trains over the not-yet-finished Lake Washington crossing by then.

Long after the full Ship Canal Bridge is smoothened, more deck work will follow across North Seattle in 2027 and beyond, so the August shakeout will become the new normal for years.

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