At about 17:49 hrs on Monday 20 March 2017, six wagons of a freight train carrying aggregates from Merehead Quarry to Acton Yard derailed at East Somerset Junction, between Westbury and Castle Cary. The accident blocked the Up Westbury line, and the train stopped when the brakes applied automatically following the parting of a coupling. There were no injuries.
The derailment occurred due to a loss of track integrity: the fixity of the right-hand rail was lost due to progressive failure of the chairscrews under the loads from freight trains traversing the curve, leading to gauge spread. The investigation identified that the design of the track was sub-optimal, following replacement of a set of points with plain line in 2010. The signs of gauge spread were not identified during inspections of the track by staff from Westbury track maintenance depot, and the section of line where the derailment occurred had not been subject to mandatory geometry measurements.
The RAIB has made four recommendations addressed to Network Rail. These cover enhancements to the company’s procedures for plain-lining of points, mitigation of risk at locations where points have previously been plain-lined, improvements to planning the operation of track measurement trains and evaluating the delivery of key track maintenance activities in the Westbury area.
The RAIB has also made a learning point, reinforcing the importance of identifying gauge spread on sections of curved track which may be subject to high lateral loads.
Published 13 December 2017