The Sodo section of the Alaskan Way Viaduct will be tightened from three lanes to two each direction starting in two weeks.

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The Sodo section of the Alaskan Way Viaduct will be tightened from three lanes to two in each direction starting in two weeks.

The May 16 lane closures mark the start of a long-dreaded, long-lasting traffic slowdown to enable replacement of the 1950s-vintage highway. Conditions will remain congested until early 2016, when a tolled tunnel is to replace the central viaduct section along the waterfront.

Construction crews in two weeks will set up on the western side of the highway, to build columns supporting new viaduct bridges over freight rails and cross streets. Two of the new columns will be built in the existing viaduct footprint and require cutting into lanes of the old viaduct.

The remaining two lanes of traffic each way will veer around the job site, between South Holgate and South King streets.

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Speed limits there will be lowered to 35 mph, instead of the current 50 mph.

To prepare for the change, Highway 99 from the West Seattle Bridge to South Lake Union will close at 11 p.m. May 13. The northbound onramp at Pioneer Square will reopen at noon May 14 so traffic can leave that night’s Sounders FC soccer match. The transition to fewer lanes begins at 5 a.m. May 16.

Project Administrator Ron Paananen of the state Department of Transportation said motorists can expect delays at commute times.

A short, northbound bus lane will be striped on the right side, from Spokane Street to South Holgate Street. This means cars entering from the West Seattle Bridge must promptly merge into one of the left two lanes so buses can roll faster on the outside.

Paananen said DOT will ask Seattle police to enforce the lane restrictions.

Next year, Sodo drivers will see a more dramatic detour, going off the highway via a frontage road alongside the stadiums, then rejoining the old viaduct at Pioneer Square.

State officials urge commuters to change trip schedules or take the bus. Some bus trips already are standing-room only.

Last year, King County Metro Transit added 31 trips to its 21 Express, 56 Express and 121 routes serving southwest neighborhoods via the viaduct, and ridership is up 11 percent, said spokeswoman Linda Thielke.

Metro is studying plans for more trips on the 54 and 120 routes this fall, she said. Quicker RapidRide service to West Seattle, Aurora Avenue North and Ballard remains a year or more away.

About 87,000 vehicles a day move through the Sodo portion of Highway 99. Those include 89 peak bus trips carrying 3,400 commuters.

Currently, Skanska USA is replacing the Sodo segment of the viaduct under a $114 million contract, to be followed by a separate contract to build a huge stadium interchange.

For years, government leaders said they would strive to finish road improvements before major viaduct reconstruction, with mixed results. Seattle DOT delivered a loop ramp last year at Fourth Avenue South along the West Seattle Bridge corridor, aided by federal stimulus cash.

But First Avenue South remains clogged; a new ramp won’t be done until fall.

Mike Lindblom: 206-515-5631 or

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