Three of the Golden Gate Bridge’s six lanes are set to close overnight this week for work on a major earthquake retrofit.

One southbound lane and two northbound lanes will remain open, allowing traffic to move in both directions. The arrangement is scheduled from 9 p.m. to 5 a.m. on weekdays and until 7 a.m. on Saturdays. This week’s final closure is set for Thursday.

Crews will use a crane to lift materials through the bridge’s suspender ropes as they build temporary work platforms. The project calls for 230,000 square feet of decking above the bay. Work will begin on the northern and southern side spans, with the main span scheduled for 2031.

The lane closures are part of a 10-year effort to strengthen the bridge against a major earthquake. Lane arrangements may change as construction progresses, but traffic is expected to keep flowing in both directions.