The National Transportation Safety Board determines that the probable cause of the derailment of the freight train was the breakage of a truck side flame of a car on the freight train which followed a progressive fatigue crack failure. The fatigue crack was probably caused by increased shock loading on the side frame due to improper application of a 40-ton spring package in a car which carried 50 tons. The breakage of the truck side resulted in damage to a turnout, which was the immediate cause of derailment of the following cars.
The cause of the collision, derailment, and damage to the passenger train was the obstruction of track No 2 by derailed cars of the freight train. The cause of injuries to the crew of the passenger train locomotive and to the crew of the freight train caboose was the absence of systematic crash protection design of the railroad equipment.