The bridge at Chestnut and Bay streets closed to all traffic Monday, June 1, so crews can upgrade the 1928 structure.
The improvements could take as long as six months, and the bridge will be closed 24 hours a day until then. Detours are posted on the street and online. Pedestrians also are being detoured around the area.
Strider Construction is doing the work for $1.58 million. When completed, the improvements will allow heavier trucks to use Chestnut Street to go between the waterfront and Interstate 5.
A bicycle lane will be added, heading south from Roeder Avenue. The left turn onto Bay Street will be eliminated.