Eastside drivers should prepare for major overnight closures and slowdowns in Bellevue next week as crews close I-405 for bridge work at NE 12th Street.

Crews will close northbound I-405 at night on August 3 and 4 from SE Eighth Street to SR 520, detouring traffic via I-90, I-5 and SR 520.

Crews will close southbound I-405 at night on August 9 and 10 from SR 520 to SE Eighth Street, with detours via SR 520, I-5 and I-90.

Crews will begin closing lanes at 8 p.m. and will close all lanes and ramps by 11 p.m., including the existing NE 12th street bridge.

During the closures, crews will hoist 10 205,000-pound concrete girders over the interstate and into position for the new 12th Street bridge.

WSDOT is building the new bridge in downtown Bellevue as part of the $107.5 million I-405 Bellevue Braids construction project funded by a combination of American Recovery and Reinvestment Act and the 2005 gas tax.

“There’s never a great time for this work, but we’re going to work at night to help keep traffic flowing during the day,” said Seema Javeri, Project Engineer. “If you’re coming through Bellevue at night, expect delays; your best bet is to avoid the area altogether.”

WSDOT and its general contractor, Atkinson Construction, are building the new NE 12th Street bridge in stages. The girders installed this summer will support a new section of bridge south of the existing bridge. Once crews finish the new southern section of the bridge, they’ll shift traffic onto it and tear down the existing bridge. Crews will then construct the north section of the bridge, connect the two sections, and open the new bridge to traffic in the summer of 2012.

The new longer and wider bridge will rise above new ramps between NE 10th Street and SR 520, and feature a new pedestrian and bike path separated from traffic.