Thirsk Rail Crash (1967) - Cause and Prevention

Cause and Prevention

The wagon derailment was blamed on excessive wear in the suspension components, thought to be caused by cement dust abrasion, in combination with slight variations in both wheel-set diameter and track alignment. This resulted in a typical "waddling", lateral oscillation of "CemFlo" tank wagons. Furthermore, it was a number of other accidents involving suspected poor riding of CemFlo wagons that resulted in progressively more severe speed restrictions being placed on any trains containing this type. At the Thirsk crash, the oscillation built up to such a state that it eventually threw the rear wheel-set of one wagon off the rails, even though the train was travelling below the maximum 45 m.p.h. (72 km/h) permitted for four-wheeled wagons. Indeed the pronounced waddling of this very train was noted by the signalman at Pilmoor in his log as he recorded its passing about 6 minutes before the derailment. Also at Pilmoor, two men were watching the trains pass. One of them had noted that the leading wheel-set of a wagon "somewhere just forward of the halfway point" had dropped heavily into the gap on a cross-over then rebounded higher than the rest. At the time, although he noted it, he thought little of it, but on hearing of the accident he felt compelled to bring this to the attention of the authorities.

Following the accident, wagon LA201 was selected for rolling-road tests at Doncaster having been judged to be in an almost identical condition to LA223 - the first vehicle to derail in the crash. As speed increased, flange-to-flange hunting (moving from side to side) was noted to set in under both laden and unladen conditions. Critical speed was noted as between 24 and 27 m.p.h. (38.4 and 43.2 km/h).

Following the accident, British Rail imposed a maximum speed of 35 m.p.h. (56 km/h) for loaded CemFlo Wagons and 50 m.p.h. (80 km/h) unloaded.