PITTSBURGH - Pittsburgh's port authority says it knows what caused a subway derailment that hampered service over the weekend.
The Port Authority of Allegheny County says Friday night's derailment happened when a train passed a stop signal and crossed a track switch that wasn't in proper position.
Spokesman Jim Ritchie said Monday it wasn't yet clear if the train's operator was at fault or if supervisors gave the driver bad information.
Ritchie says the driver involved in the derailment has been suspended with pay.
Nine people were on board the train when it went off the rails beneath downtown. Three minor injuries were reported.
Normal service resumed Monday.