Drivers entering Seattle from the north and east should allow extra time to bypass a pair of construction projects this weekend that will close lanes on Interstate 5 and Highway 520.

In North Seattle, the I-5 Express Lanes, which go seven miles from Northgate to downtown, will close from 9 p.m. Friday until 5 a.m. Monday, so contractors can deliver a prefabricated span of the Northgate walk-bike bridge. The span will be temporarily stored on the freeway median.

The new bridge across the freeway is scheduled to be finished at or near the September start of Sound Transit light-rail service to U District, Roosevelt and Northgate stations. The walk-bike crossing provides a direct path between the Northgate transit hub and North Seattle College, as well as neighborhoods between Aurora Avenue North and Northgate.

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Additional lane closures will be needed to deliver a second span and then assemble the bridge over I-5. Construction detours will occur overnights and on weekends, the Seattle Department of Transportation says.

This bridge span, built by Jesse Engineering in Tacoma, will be delivered to I-5 near Northgate this weekend, and later hoisted to form a new walk-bike route over the freeway. (Seattle Department of Transportation photo)

At Highway 520, state contractors building the new Montlake lid will close the westbound bridge and ramps this weekend so they can attach more concrete girders above the lanes. That shutdown will last from 11 p.m. Friday until 5 a.m. Monday, from 92nd Avenue Northeast in Yarrow Point to the Montlake Boulevard/University of Washington exit.

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The walk-bike trail and eastbound lanes remain open, along with highway access west from Montlake to I-5.

A similar eastbound closure is planned a weekend later. The 520 bridge’s Montlake segment, including spans over the lake shore, is expected to be finished in 2023 or 2024.

The First Avenue South bridge’s northbound roadway will be reduced from four lanes to two, so crews can repair the steel drawspan deck this Sunday, Feb. 28, from 6 a.m. to noon.

And then the night of March 5, several days of First Avenue South bridge repair will require overnight full closures and 24-hour lane closures southbound, to replace worn-out bearings under the decks.