The Market-Frankford Line trains were near the 69th Street Transportation Center on a loop where trains turn around to get back into service, said Andrew Busch, a spokesman for the Southeastern Pennsylvania Transportation Authority. One train was waiting to head back to downtown Philadelphia when it was hit from behind, Busch said. The derailed cars hit another train, which also was waiting to go back in service.
The train that was rear-ended had passengers on board, and Busch said it's not clear why, since it wasn't in service. Two passengers were among the injured, and Busch didn't have details on them, except to say they have been described as non-life threatening.
The National Transportation Safety Board said three investigators were heading to the site of the collision and derailment. Service was restored on the Market-Frankford line later Tuesday afternoon, ahead of the evening rush, Busch said.
The crash is the latest ordeal for the Market-Frankford line, which runs as a subway downtown and is elevated in west and northeast Philadelphia. Earlier this month, SEPTA took dozens of cars out of service after a crack was found on a main load-carrying beam on a car on the line.
The reduced fleet had caused some disruptions but the agency was approaching full service on the line.