A portion of Aurora Avenue North will close this weekend. On Monday, drivers will be diverted to a new curved overpass in South Lake Union.

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A stretch of Aurora Avenue North in Seattle will close this weekend while construction workers shift its current four lanes onto a new roadway at South Lake Union.

When commuters return Monday morning, they’ll be driving on a curved overpass that will be in use for at least two years, until tunnel-boring machine Bertha arrives and the new Highway 99 tunnel is finally completed.

The big curve — 750 feet of roadway shifted west — will create space for Atkinson Construction to finish building the connection from the northbound tunnel to northbound Aurora, plus the future exit ramp from the tunnel to Republican Street.

During the detour period, lane capacity will remain the same. Southbound travelers will still see two exit lanes at Denny Way, while two lanes continue through the old Battery Street Tunnel onto the Alaskan Way Viaduct.

Dave Sowers, Highway 99 deputy administrator for the Washington State Department of Transportation, predicts minor slowdowns early next week, because the curve offers a potentially distracting view of the future deep-bore tunnel entrance.

“There will be some rubberneckers who will try to look into the portals, so people will need a little time to get used to that,” Sowers said.

When the Highway 99 tunnel is completed, bypassing downtown, this curved overpass will become the connection between Aurora and downtown surface streets.

Atkinson Construction is on schedule and budget with its $41 million contract to build the north-side tunnel approach. That’s not the case for the main $1.35 billion contract with Seattle Tunnel Partners, whose drilling machine Bertha is being repaired, following its breakdown Dec. 6, 2013. It is estimated that the deep-bore tunnel will open in March 2018.

If Bertha had arrived on schedule, for a planned December 2015 tunnel opening, this kink in Aurora would need to exist only a few months. But because of delays, the Aurora Avenue curve will remain until perhaps early 2018.

The section of Aurora at South Lake Union will close from 10 p.m. Friday until 5 a.m. Monday.