Jacksonville’s Main Street bridge will be closed from 6:30 p.m. Friday through 8 a.m. Sunday, and again from 6:30 p.m. Friday, Sept. 16 to 8 a.m. Sunday, Sept. 18, due to planned work to improve its mechanical, electrical and structural systems. The Florida Department of Transportation said vehicular and pedestrian traffic will be detoured to the Acosta Bridge during the two weekend Main Street bridge closures.