Update: As of 11:20 p.m., crews were wrapping up asphalt repairs, says Maryland Transportation Authority spokeswoman Terri Moss. The left-hand tube of the southbound tunnel would also undergo scheduled maintenance, she said, but was supposed to reopen by 5 a.m. Friday -- in time for rush hour.

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Serious backups developed on Interstate 95 at the Fort Mchenry Tunnel after the Maryland Transprtation Authority closed the left-hand tube of southbound tunnel for repair of heat-related damage Thursday, leaving only two of four lanes in operation.

The two lanes of the right-hand tube remained open, but the closing -- which came just as the evening rush hour was getting started -- had traffic at a virtual standstill until well after 7 p.m. The state's CHART system cameras showed serious backups extending at least as far back as the I-95/I-895 split.

Authority spokeswoman Teri Moss said two concrete slabs rose 4 inches and buckled because of the heat. Crews were jackhammering and patching the damage. Cheryl Sparks, another authority spokeswoman, said repairs were expected to be completed in time for the morning rush hour. She said that as of 7:30 p.m. traffic was backed up about a half-mile approaching the tunnel.

The authority suggested that southbound travelers on Interstate 95 divert to Interstate 895 and use the Harbor Tunnel. Motorists could also use Interstate 695 and the Francis Scott Key Bridge.