Both directions of Interstate 405 will close all day Saturday while crews dig out and replace a collapsed culvert in south Bellevue, which state officials said might otherwise cause a sinkhole in the road.

The freeway blockage will constrict suburban traffic and frustrate Husky football fans from the Eastside attending Saturday’s 4:30 p.m. home game against Michigan State.

The work zone is a short distance south of Interstate 90 at Exit 9, the 112th Avenue Southeast/Lake Washington Boulevard interchange, which averaged 147,000 mainline trips per day last year.

The Washington State Department of Transportation said the failed culvert caused a 15-foot-deep sinkhole this spring in the Newport Hills Park-and-Ride, and “has the potential to cause similar sinkholes under mainline I-405.” Culverts are pipes or concrete basins where small streams flow beneath a roadway, sometimes along critical fish migration routes.

The announced I-405 work phases are:

  • Thursday from 11 p.m. – 5 p.m. Friday: The southbound Exit 9 offramp will close most of Friday, while the mainline shrinks to two lanes from Exit 10 at Coal Creek Parkway until after Exit 9.
  • A 23-hour closure, from 11 p.m. Friday until 10 p.m. Saturday, affecting the entire mainline. Flaggers will be herding all traffic off the freeway and around the work zone using Exit 9 ramps.
  • A Sunday closure of the Exit 9 onramp to northbound I-405 from 11 p.m. Saturday until 9 p.m. Sunday.

Also this weekend, the I-90 floating bridge bike lane will close all weekend, along with the West Mercer Way onramp to westbound I-90, from 10 a.m. Friday until early Monday as the state prepares for a huge joint replacement project Sept. 23-26.

On the Seattle side of Lake Washington, WSDOT said Thursday morning it will cancel previous plans to close three southbound lanes of I-5. The whole mainline and downtown auxiliary lanes will remain open, except for a shutdown of the Columbian Way/West Seattle Bridge off-ramp from Friday evening until 6 a.m. Sunday.


Drivers will be able to directly reach the West Seattle Bridge exit Sunday when the city reopens the seven-lane span, after a two-year shutdown for crack repairs.


“This is a big deal for a lot of people, and the last thing we want to do is interfere with people’s ability to use the West Seattle Bridge and enjoy West Seattle,” spokesperson Tom Pearce said.

City transportation managers won’t reveal the exact hour Sunday the West Seattle Bridge reopens because drivers might cluster around the onramps to be first across, program manager Heather Marx said.

In addition to the Huskies game, the Washington State Fair in Puyallup, along with concerts in Seattle and Woodinville, will attract drivers who normally take I-405, state officials warn.

Sound Transit light rail is running at normal 10-minute frequency between Northgate and Angle Lake. The west stairwell at Northgate Station will close Saturday for maintenance, while as of midweek, a total of 12 escalators and two elevators were inoperable within the four downtown stations.

Washington State Ferries, while still struggling with chronic crew shortages, has restored full two-boat service on the Mukilteo-Clinton and Seattle-Bainbridge routes, and sometimes can add a second boat on the Edmonds-Kingston route.

Next week, WSDOT will resume construction on westbound I-90 approaching Issaquah, where traffic will shrink to one lane from 9 p.m. Sunday until 5 a.m. Friday, causing traffic delays. Crews are resurfacing a one-mile segment where runoff inside an abandoned coal mine seeped under the freeway, leading to cracks.