Demolition to close part of I-405 three weekends in August

The Wilburton Tunnel on Interstate 405 in Bellevue will be demolished during three weekends next month, causing traffic ripples around Lake Washington and back.

During the second, third and fourth weekends of August, the southbound freeway lanes will completely close from late Friday to early Monday.

Traffic jams will be their worst from 10 a.m. to 7 p.m. those days, state officials predict.

"If you're going to go visit friends, tell them you're coming for coffee and staying for dinner," said Stacy Tussler, deputy project director. "Even with reduced travel, drivers should give themselves two extra hours to get around the region," she said.

During the demolition, Eastside motorists are urged to go around the blockage and drive through Seattle — even if that means backtracking. Officials recommend reaching Interstate 5 from I-405 via Lynnwood, from Highway 522 via Kenmore, or from westbound Highway 520 across the lake. Those who do use I-405 will have to exit at Southeast Eighth Street and follow orange-detour signs to side roads.

The Wilburton Tunnel, built in 1972, is being removed to create space for a freeway widening, paid for by state gas-tax increases. By the end of next year, the southbound HOV exit lane from I-405 to I-90 will be extended back to Southeast Eighth Street, and one general-purpose lane will be added.

On a normal Saturday, about 98,000 vehicles go through the southbound lanes, Tussler said.

Signs on I-5 in Snohomish County will encourage drivers to continue through Seattle instead of entering I-405. Lane closures on the Eastside will begin north of Highway 520.

A year ago, the Department of Transportation issued warnings that an I-5 repair job in Seattle would cause traffic jams far past Tukwila. But motorists adapted by avoiding trips or riding transit, so the backups rarely went beyond three miles.

This time, Tussler said the DOT expects people will make 20 percent fewer trips and that most drivers will detour north of downtown Bellevue.

One-third of the concrete tunnel will be sliced and broken off each weekend. A wrecking ball and crunching machines will twist the rebar and break the concrete into softball-sized pieces.

A stretch of abandoned BNSF Railway track, which ran diagonally atop the tunnel, has already been removed. It might be replaced someday with a bike lane or transit tracks, using a new bridge.

Crews on another project, in Renton, will take advantage of reduced I-405 traffic to work on a bridge over Oakesdale Avenue Southwest the weekend of Aug. 8-10. The southbound freeway will be down to one lane until Saturday morning, then two lanes through that weekend.

Mike Lindblom: 206-515-5631 or mlindblom@seattletimes.com