PHILADELPHIA >> Officials are investigating an accident involving two out-of-service commuter trains in suburban Philadelphia that injured four railroad workers.

The Southeastern Pennsylvania Transportation Authority says the Market-Frankford Line trains were travelling near the 69th Street Transportation Center when the accident occurred Tuesday morning.

Television news footage shows several cars have derailed and one is tipped over at a 45-degree angle.

Upper Darby police Superintendent Michael Chitwood says four SEPTA workers were injured but none of the injuries appeared life-threatening.

SEPTA says the cause of the accident is under investigation.

Shuttle buses are running between 69th Street Transportation Center and 63rd Street Station.