UPPER DARBY, Pa. (CBSNewYork) — Forty-two people, including a train conductor, were injured after one commuter train rear-ended an empty train parked at a station in suburban Philadelphia.

SEPTA, the Southeastern Pennsylvania Transportation Authority, said the crash happened around 12:15 a.m. Tuesday at the 69th Street terminal in Upper Darby.

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Four people suffered serious injuries.

The cause of the crash remains under investigation.

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