Aurora Avenue North and Mercer Street will be closed where the two busy streets cross until 5 a.m. Monday, so equipment can be moved into place for a two-year, $95 million widening of the Mercer underpass to accommodate two-way traffic, and to add bike trail and sidewalks.

During the closure, signs will instruct traffic from the north to leave Aurora at North 85th Street, and a police officer will direct traffic. But local vehicles will be allowed through as far as Valley Street along east Queen Anne Hill.

From the south, drivers going beyond downtown will be instructed to leave Highway 99 just before Spokane Street, however northbound lanes will remain open to the Seneca Street and Western Avenue exits. The Battery Street Tunnel will be closed.

Mercer Street will close near Aurora, forcing motorists to detour using Fifth Avenue North, Denny Way and other streets.

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For two years starting Monday, eastbound Mercer Street will be reduced from four lanes to two near Aurora while a stretch of Broad Street will reopen eastbound to drain off some of the resulting congestion.

More details are on the “Mercer West” homepage,