A three-mile stretch of Interstate 95 was shut down early Tuesday, backing up commuter traffic for miles, as workers began emergency repairs on a 6-foot crack in a concrete pillar supporting the major corridor through the Northeast.

The work required closure of both northbound and southbound lanes of the highway north of the city's central business district, Pennsylvania Department of Transportation spokesman Gene Blaum said.

The fracture ranged from 2 inches to several inches wide. "Obviously, we feel it could compromise the strength of that section of the highway," Blaum said.

The section of the interstate carries about 190,000 vehicles a day, making the repair "a major undertaking," he said.

Traffic rapidly snarled at exit points as police directed motorists onto detours around the damaged area.

PennDOT planned to have a contractor erect four steel towers to surround and support the steel-reinforced concrete pillar before the highway could be reopened. Officials said the work would take two to four days.

On Tuesday morning, workers were clearing concrete barriers so heavy equipment could be moved closer to the damaged pillar and were starting work on the foundation for the temporary towers.

"Fortunately it was found, we're on top of it, and we're taking care of the situation," Mayor Michael Nutter said.

A crack about a half-inch wide was noticed by an inspector last fall. The same inspector happened to be in the area Monday and decided to check the cracked pillar, Blaum said.

"This crack has grown considerably since October," Blaum said. "It was very fortuitous that he took that look today."

Concrete at the top of the column was crumbling, leaving reinforcing rods visible from the street below, and brick-sized chunks of concrete had fallen around the base of the pillar.

Blaum said engineers weren't sure what caused the crack in the 40-year-old pillar. The column is located under an expansion joint, and it's possible the damage may have been caused by expansion and contraction of the roadway, Blaum said.

"Obviously this is certainly not something we would do unless it is absolutely necessary, to shut down the interstate, but it's going to be done," Blaum said. "Two spans of Interstate 95 basically connect right on top of that column."

Blaum said the highway's other supports in the area weren't showing similar deterioration. Several sections of I-95, including the column in question, had been scheduled for repair later this year, Blaum said. There's also a $2 billion plan in the works to replace five sections of roadway, including the area with the damaged pillar, in the next 10 to 15 years, Blaum said.