​​CSX freight train extra 7592 north had the 44th car derail at a rail joint of the railroad crossing in the Soo Line's Spring Hill interlocking. The joint had compromise joint bars, connecting rails of different sizes. The derailed car struck a switch and initiated an emergency application of the brakes which resulted in a secondary derailment of the 74th through 105th cars. Examination revealed that the ballast under the joint was fouled with mud and had been “pumping" to the extent that a joint bar was cracked. The rail joint was 1-3/8 inches lower than the uniform track profile. The train was traveling 56 mph through a 50 mph maximum permissible speed area. Maintenance of the joint was the responsibility of the Soo Line, although CSX personnel regularly traveled over it during their routine inspections, and had repaired the joint when the original had broken in October of 1990. Train makeup had empty cars on the head end and loads at the rear.

Note: This investigation was published as a summary in RAB-93-02, Railroad Accident Briefs - Brief Format of 1991 Accidents.

​​The probable cause of this accident was the failure of Soo Line and CSX to properly maintain the rail joint on the northeast corner of the crossing diamond. Contributing to the accident was excessive train speed and the improper placement of loaded cars at the rear of the train.