At 10:17 p.m., on April 27, 1972, eight cars in Penn Central freight train B-4 derailed as the train was moving at about 8 m.p.h. into the Potomac Yard in Arlington, Va. One of the derailed cars fouled the adjacent No. 2 main track of the Richmond, Fredericksburg and Potomac Railroad Company and was struck by Southern Railway passenger train No. 6 about 6 to 8 minutes later. The four-unit diesel-electric locomotive of the passenger train and the three occupied passenger cars were derailed. There were no serious injuries.