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The Seattle area’s most grueling road-construction season in seven years kicks off this weekend with the closure of the Highway 520 floating bridge, until 5 a.m. Monday.

Then comes a series of projects next weekend on northbound Interstate 5, the southbound Alaskan Way Viaduct, and again at Highway 520.

The 520 bridge is closed this weekend and for three of the next four, but stays open June 14-15 because of that Saturday’s graduation ceremonies at the University of Washington.

Some I-5 drivers will face a double shot of congestion next weekend, because one or two lanes of the northbound Ship Canal Bridge will be closed for concrete and guardrail repairs — at the same time two lanes are shut to replace expansion joints on the West Seattle Bridge.

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That joint replacement was supposed to happen in April but weekend rains delayed it, said Kris Olsen, spokeswoman for the Washington State Department of Transportation. The job requires dry conditions for polyester-infused concrete fillings to harden over the highway ruts and edges.

Meanwhile, the Mercer Street Corridor in Seattle will be converted this weekend from east-only to two-way traffic on Mercer between Fifth and Ninth avenues north, a job that will require occasional closures Sunday afternoon, said project manager Eric Tweit. The nearby Broad Street underpass will permanently close by Monday morning.

Other significant projects include overnight lane closures to replace 300 concrete panels of I-5 in North Seattle, starting in July. On the Eastside, expansion-joint work will bring a seven-day, three-lane closure of the westbound East Channel Bridge of Interstate 90 from Bellevue to Mercer Island, in mid-July.

There will also be many night closures, starting this weekend.

In Seattle, the southbound I-5 collector-distributor lanes — which lead to I-90, the stadiums, and Airport Way South — will close from 11 p.m. Saturday until 8:30 a.m. Sunday. The closure also will block the Spring Street ramp from downtown to I-5.

Throughout late summer and fall, contractors will close lanes of surface Highway 99 through Sodo, to replace 81 worn-out concrete panels

All these projects add up to the most summer disruption since August 2007, when drivers on northbound I-5 experienced delays of up to three miles or 45 minutes near the I-90 junction, site of a two-week expansion-joint repair. Then in October 2011, the “Viadoom” closure for Highway 99 demolition caused widespread congestion on two of its five weekdays.

“It’s hard to predict what the backups are going to be,” Olsen said. If drivers reschedule their trips or take transit, she said, they’ll be more manageable.

Mike Lindblom: 206-515-5631 or On Twitter @mikelindblom

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