Eastside drivers will have an especially tough time this weekend when a 5-mile stretch of Interstate 405 closes in both directions, while contractors dig a giant trench to install a stream culvert.
And that’s just one of at least seven Seattle-area transit and traffic disruptions, in the heat of summer construction season.
At I-405, all lanes will close between the Highway 900/Sunset Boulevard interchange in Renton, and Coal Creek Parkway in Bellevue, from 10 p.m. Friday until 4:30 a.m. Monday.
The job will disrupt travel plans for about 400,000 drivers who go through Renton on a typical weekend, said project director Sharif Shaklawun.
Project spokesperson Craig Smiley encouraged motorists to cancel or delay I-405 travel.
The Washington State Department of Transportation will mark a detour along north-south Coal Creek Parkway Southeast and Highway 900. That route typically takes 15 minutes but will be slower when filled by diverted traffic, said Smiley. Signal retiming and traffic police will help move cars, but arterial lanes through the city of Newcastle are no match for a freeway, he said.
The Highway 520 bridge will stay open but its Montlake Boulevard interchange ramps, and the boulevard above the highway, will close this weekend from 10 p.m. Friday to 6 a.m. Monday.
A shutdown of eastbound Highway 518, from Des Moines Memorial Drive South to International Boulevard South, will obstruct traffic from Burien to Seattle-Tacoma International Airport. That shutdown, to repair an overpass damaged by a tall truckload, lasts from 9 p.m. Friday to 5 a.m. Monday. A marked side-street detour will be available.
Drivers on southbound Highway 167 will be slowed by bridge surface repairs just north of Highway 516 in downtown Kent, where traffic will shrink to a single lane between 10 p.m. Friday and 5 a.m. Monday.
In Seattle, onramps from Mercer Street to both northbound Interstate 5 and the I-5 express lanes will close from 9 p.m. Friday until 4 a.m. Monday, and again the following weekend for work on a future high-occupancy express lane.
Routine overnight maintenance of Interstate 90 will block two westbound lanes from Mercer Island to Seattle, scheduled for 10 p.m. Friday until 6 a.m. Saturday.
Sound Transit’s light-rail 1 Line will run at a reduced frequency of 20 minutes between trains and require riders to change trains at Pioneer Square Station, as work continues to replace sinking rails near Stadium Station.
Heavy roadwork
Drivers from Renton to Bellevue can already see new retaining walls and noise walls for miles, as contractor Flatiron Construction prepares to widen the I-405 mainline by one lane each direction.
The $705 million renovation will result in a layout of two general lanes and two high-occupancy/toll lanes each direction, plus some exit-only lanes, by late summer 2025. The freeway segment in Renton hasn’t been widened since 1984.
A concrete bridge is taking shape above Northeast 44th Street. WSDOT will shift all six mainline lanes onto that structure in September for two years. It will become the permanent northbound lanes in 2025, when a twin freeway bridge for southbound lanes is completed.
New culverts are required by a federal court order to improve blocked salmon streams and tributaries, as part of the state’s treaty promises to respect Indigenous tribes’ usual and accustomed fishing grounds.
Contractors this weekend will excavate a 209-foot-long trench across I-405, near the Seahawks training center in north Renton, and then fasten a series of precast concrete box pieces 30 feet below road decks. Water from three unnamed creeks will commingle in the new passage and flow toward Lake Washington.
A similar installation will block I-405 again Sept. 9-10.
Workers this weekend will also repair expansion joints, continue overpass construction and install equipment for travel-information signs.
“We know this is painful. We want to get as much work done as we possibly can. We want construction workers to be safe and we want the public to be safe,” said Smiley.
Correction: An earlier version of this story mistakenly said the eastbound Highway 518 closure would obstruct traffic from Seattle-Tacoma International Airport to Burien. The closure will block traffic the other way, from Burien to the airport.
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