The Maine Department of Transportation closed one lane of the Interstate 295 bridge over the Presumpscot River at 3 p.m. after a year-old steel joint broke loose.

Traffic on the southbound lanes of the busy thoroughfare is down to one lane starting as crews rip up the concrete to replace the joint, said MDOT spokesman Ted Talbot. If repairs go smoothly, the road should reopen by midnight.

The bridge is at Mile 9, the Portland-Falmouth town line.