Report 07/2020
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Rail Accident Report Freight train derailment at Willesden High Level Junction, north-west London 6 May 2019 Report 07/2020 August 2020 This investigation was carried out in accordance with: l the Railway Safety Directive 2004/49/EC l the Railways and Transport Safety Act 2003 l the Railways (Accident Investigation and Reporting) Regulations 2005. © Crown copyright 2020 You may re-use this document/publication (not including departmental or agency logos) free of charge in any format or medium. You must re-use it accurately and not in a misleading context. The material must be acknowledged as Crown copyright and you must give the title of the source publication. Where we have identified any third party copyright material you will need to obtain permission from the copyright holders concerned. This document/publication is also available at www.gov.uk/raib. Any enquiries about this publication should be sent to: RAIB Email: [email protected] The Wharf Telephone: 01332 253300 Stores Road Website: www.gov.uk/raib Derby UK DE21 4BA This report is published by the Rail Accident Investigation Branch, Department for Transport. Preface Preface The purpose of a Rail Accident Investigation Branch (RAIB) investigation is to improve railway safety by preventing future railway accidents or by mitigating their consequences. It is not the purpose of such an investigation to establish blame or liability. Accordingly, it is inappropriate that RAIB reports should be used to assign fault or blame, or determine liability, since neither the investigation nor the reporting process has been undertaken for that purpose. RAIB’s findings are based on its own evaluation of the evidence that was available at the time of the investigation and are intended to explain what happened, and why, in a fair and unbiased manner. Where RAIB has described a factor as being linked to cause and the term is unqualified, this means that RAIB has satisfied itself that the evidence supports both the presence of the factor and its direct relevance to the causation of the accident or incident that is being investigated. However, where RAIB is less confident about the existence of a factor, or its role in the causation of the accident or incident, RAIB will qualify its findings by use of words such as ‘probable’ or ‘possible’, as appropriate. Where there is more than one potential explanation RAIB may describe one factor as being ‘more’ or ‘less’ likely than the other. In some cases factors are described as ‘underlying’. Such factors are also relevant to the causation of the accident or incident but are associated with the underlying management arrangements or organisational issues (such as working culture). Where necessary, words such as ‘probable’ or ‘possible’ can also be used to qualify ‘underlying factor’. Use of the word ‘probable’ means that, although it is considered highly likely that the factor applied, some small element of uncertainty remains. Use of the word ‘possible’ means that, although there is some evidence that supports this factor, there remains a more significant degree of uncertainty. An ‘observation’ is a safety issue discovered as part of the investigation that is not considered to be causal or underlying to the accident or incident being investigated, but does deserve scrutiny because of a perceived potential for safety learning. The above terms are intended to assist readers’ interpretation of the report, and to provide suitable explanations where uncertainty remains. The report should therefore be interpreted as the view of RAIB, expressed with the sole purpose of improving railway safety. Any information about casualties is based on figures provided to RAIB from various sources. Considerations of personal privacy may mean that not all of the actual effects of the event are recorded in the report. RAIB recognises that sudden unexpected events can have both short- and long-term consequences for the physical and/or mental health of people who were involved, both directly and indirectly, in what happened. RAIB’s investigation (including its scope, methods, conclusions and recommendations) is independent of any inquest or fatal accident inquiry, and all other investigations, including those carried out by the safety authority, police or railway industry. Report 07/2020 August 2020 Willesden High Level Jn This page is intentionally left blank Report 07/2020 4 August 2020 Willesden High Level Jn Freight train derailment at Willesden High Level Junction, north-west London, 6 May 2019 Contents Preface 3 Summary 7 Introduction 8 Definitions 8 The accident 9 Summary of the accident 9 Context 11 The sequence of events 17 Background information 19 Analysis 30 Identification of the immediate cause 30 Identification of causal factors 30 Identification of possible underlying factor 48 Observations 49 Previous occurrences of a similar character 50 Summary of conclusions 52 Immediate cause 52 Causal factors 52 Underlying factor 53 Additional observations 53 Previous RAIB recommendations relevant to this investigation 54 Actions reported that address factors which otherwise would have resulted in a RAIB recommendation 57 Other reported actions 58 Recommendations and learning points 59 Recommendations 59 Learning points 61 Appendices 62 Appendix A - Glossary of abbreviations and acronyms 62 Report 07/2020 5 August 2020 Willesden High Level Jn This page is intentionally left blank Report 07/2020 6 August 2020 Willesden High Level Jn Summary Summary At around 21:30 hrs on 6 May 2019 a single wagon in a freight train derailed on a curve approaching Willesden High Level Junction in north-west London. The wagon re-railed as it passed over the junction. Although no-one was injured, a derailment like this has the potential to foul lines that are open to passenger traffic or strike structures. The track was supported by an earth embankment that Network Rail had been monitoring since October 2016, and which was showing signs of progressive seasonal movement. The empty two-axle wagon derailed where the track cross-level had been changing. Derailment occurred because the wagon encountered a significant track twist and had an uneven wheel load distribution. This combination resulted in there being insufficient load at the leading left-hand wheel to prevent the wheel flange climbing over the railhead. A check rail would have prevented the derailment. Network Rail had completed a risk assessment that had concluded this safeguard was not necessary on the small-radius curve. The track twist had developed rapidly. This was because of the poor condition of the earth embankment and the loss of ballast support from under the sleepers. The measures that Network Rail had in place for inspection, maintenance and mitigation were not effective in detecting this risk and protecting the safe running of trains. The wagon had a diagonal wheel load imbalance. This arose because the suspension adjustment arrangement was susceptible to introducing an imbalance of this type and routine maintenance had not detected that it was present. Within Network Rail, separate teams are responsible for track maintenance and earthwork management. RAIB has identified the lack of sharing of information between these teams as a possible underlying factor. RAIB has made four recommendations: l Three are directed to Network Rail and concern: • the use, and limitations, of information from its track geometry measurement trains for understanding the condition of the track and problems with the track bed and/or supporting earthwork structures, and how this may affect the safe running of trains • measures to mitigate the risks arising from known defects in supporting earthwork structures. l One is directed at DB Cargo, the owner and maintainer of the derailed wagon, relating to the maintenance of this and similar two-axle wagons. RAIB has additionally identified learning points concerned with indications of poor track bed condition, the importance of good liaison between track maintenance and earthwork management teams and the management of wagon diagonal wheel load imbalance. Report 07/2020 7 August 2020 Willesden High Level Jn Introduction Introduction Definitions 1 Metric units are used in this report, except when it is normal railway practice to give speeds and locations in imperial units. Where appropriate the equivalent metric value is also given. 2 All mileages in the report are taken from a datum at Mitre Bridge Junction. Left and right orientations relate to the direction of travel of the train. 3 The report contains abbreviations. These are explained in Appendix A. Report 07/2020 8 August 2020 Willesden High Level Jn The accident Summary of the accident The accident 4 At around 21:30 hrs on 6 May 2019, a single wagon, within freight train 6L36,1 derailed on elevated curved track approaching Willesden High Level Junction in north-west London (figure 1). Train 6L36 was the scheduled 19:45 hrs service from Hoo Junction Up Yard, in Kent. It was carrying material from an engineering worksite, near Lewisham, to Network Rail’s recycling facility and marshalling yard at Whitemoor, in Cambridgeshire. 5 The 21-wagon train had been routed from the down West London line to the up High Level line at Mitre Bridge Junction and was stopped at NL1048 signal, on the approach to Willesden High Level Junction (figure 2). The 20th wagon on the train derailed to the left around 30 seconds after the train started to move again. The train was travelling at 7.8 mph (12.6 km/h). The wagon re-railed as it crossed over the switch and crossing layout at Willesden High Level Junction. No other wagons derailed. The driver was unaware of the derailment. However, signallers observed an axle counter2 failure at the junction after the train had passed and brought it to a stand at Hampstead Heath to check that the train had not divided. The driver was given permission to continue once this had been confirmed.