The accident at Sheffield station on 11 November 2020, in which several cement wagons derailed, was due to gauge widening caused by broken track screws, a report by the Rail Accident Investigation Branch (RAIB) has revealed.
The freight train, which was made up of a Class 66 locomotive hauling 34 wagons conveying cement powder from Hope, Derbyshire, to Dewsbury, West Yorkshire, derailed at the north end of Sheffield station at 02:44 on Wednesday 11 November 2020. A number of wagons were damaged, 16 of them derailed with one ending up on its side, and there was significant damage to the track, resulting in a partial closure of the station. No one was injured.
The accident partially closed Sheffield station for five days while investigations took place, the damaged wagons recovered and track and signalling equipment repaired.
The RAIB investigation determined that the train was coasting through the station at a constant speed of around 12mph (19km/h) when the leading right-hand wheel of the twelfth wagon dropped into the space between the two running rails (the ‘four-foot’). At this point, the rails were too far apart – a problem known as gauge widening.
The train stopped when the signaller observed a number of signalling equipment failures indicated on a display screen and alerted the driver to a problem.
The track gauge had widened because a number of track screws, which secured the rails and baseplates to the wooden bearers, had broken, allowing the rails to spread apart under the loads from passing trains.
Having examined the failed items, the RAIB concluded that the track screws had failed several weeks, or perhaps months, before the derailment, but the failures had not been identified by Network Rail’s maintenance inspection activities. The report notes that, although this was a location with a potentially high risk of derailment, it had not been recognised as such because Network Rail’s guidance for identifying such risk had not been applied. Additional mitigation had therefore not been considered.
In its conclusions, the RAIB has made four recommendations to Network Rail concerning the implementation of processes for identifying high derailment risk locations, the implementation of safety-critical changes to its processes, standards governing fitment of check rails, and track geometry data formats.
It has also identified three learning points for track maintenance staff alerting them to the need for effective management of track gauge in tightly curved track, the limitations of geometry alerts provided by static measuring equipment, and the importance of monitoring track geometry trends for the identification of track deterioration.
- Network Rail should review its processes for the application of site- specific derailment risk assessments, such as those implemented by track work instruction TWI 3G130 and make and brief any necessary changes so that they are fully and consistently implemented by track maintenance staff.
- Network Rail should review its arrangements for how safety-critical changes to the management of track maintenance are incorporated into its processes and procedures, including consideration of management assurance of compliance. In particular, this review should include consideration of how Network Rail determines whether such changes should be implemented as standards or as guidance. Network Rail should make and brief any revisions necessary to facilitate appropriate, consistent and
- Network Rail should review, and update and brief as necessary, its standards and processes relating to the fitment of check rails to clarify their applicability, or otherwise, to tight track radius locations inside switches and crossings as a means of managing derailment risk.
- Network Rail should review, and change as necessary, the format of the data produced by its MPV track recording unit, geometry recording trolleys and other measurement systems, and analysis tools, so that track maintenance staff can routinely and easily identify fault locations and perform trend analysis of track geometry. This recommendation reinforces recommendation 1 from RAIB’s investigation into the freight train derailment at Willesden High Level junction on 6 May 2019, and could be incorporated into the work resulting from it.
- The importance of track maintenance staff implementing effective management of track gauge, particularly in locations of high curvature with no check rail, where this is not monitored by track recording trains.
- The importance of track maintenance staff using static geometry measurement equipment, such as recording trolleys, recognising that, although pre-programmed to generate alerts related to dynamic gauge intervention limits, they only record static measurements. Users need to assess dynamic movement by alternative means and take this into account when assessing whether maintenance intervention is necessary.
- The importance of routinely gathering and analysing dynamic geometry data, and its trends, to identify potential deterioration of track and its fixings.