Potters Bar Rail Accident Investigation

The effectiveness of the guidance contained in Network Rail Company Code of Practice RT/E/C/10179, The Set Up and Maintenance of Adjustable Stretcher Bars - A Good Practice Guide, in relation to the positioning and tightening of stretcher bar nuts, should be reviewed following in-service experience. The guidance should, if necessary, be modified in the light of this review and the results of the research carried out into the tightening of nuts on adjustable stretcher bars.

A training programme based on the guidance contained in Network Rail Company Code of Practice RT/E/C/10179, The Set Up and Maintenance of Adjustable Stretcher Bars - A Good Practice Guide should be developed. All signal installation and maintenance staff, their supervisors and managers, should be trained in accordance with that programme and assessed as competent.

A system of managerial controls to mitigate the risks associated with adjustable stretcher bar assemblies should be developed and implemented.

The requirements for reporting loose and missing nuts on adjustable stretcher bars should be reviewed. This review should consider the need for fault reporting systems to distinguish between different types of stretcher bars.

Railway Group Standards relating to the maintenance and inspection of safety critical systems should require Railway Group members to assess the value of obtaining performance feedback through recording and analysis of corrected defects, and if necessary introduce appropriate measures as part of inspection and maintenance procedures.

Consideration should be given to whether the design of crank pivots should be improved, and/or whether the inspection regime should be improved to allow earlier detection of failures of Spirol pins.

Requirements for the quality control of insulating bushes procured for use on adjustable stretcher bars should be reviewed and enhanced where necessary.

Railway Group Standard GI/RT7004 and all Network Rail technical documents covering installation, inspection and maintenance of point flangeway gaps, including the opening at the switch toes, should be reviewed, and, where necessary, modified, in order to: • Use consistent terminology. • Remove ambiguities. • Be consistent with the dimensions contained in RT/E/C/11772. • Specify the depth and longitudinal position at which the flangeway gap dimensions are to be measured.

A requirement should be introduced for flangeway gaps and supplementary drive settings on points to be checked together at defined intervals as part of maintenance.

Network Rail Company Standards RT/E/C/11772, RT/E/C/11210 and/or associated drawing BRS-SM 2370/2 & /8 should be modified so that they are consistent in respect of the specification for excess motion setting and of the terminology used.

The specification of SMS PA21 should be revised to set out in more detail the checks required to be carried out under services A and B, in addition to the FPL test.

Signallers and technicians should have a common understanding of the types of work that are permissible under Clause 3.3 of Module T1A of the Rule Book GE/RT8000.

Consideration should be given to revising the requirements for setting flangeway clearances in points in order to avoid contact between the flangebacks of wheels and open switch rails over the permissible ranges of wheelset and track geometry. The revision should take into account the permissible geometry of wheelsets of vehicles operating in international traffic and the relevant implications of any emerging European Standards dealing with wheel and rail geometry.

Taking into account the outcome of the action recommended in 13 above, consideration should be given to increasing the minimum allowable flangeway gap between open switch rails and stock rails in situations where wide gauge is found in points and cannot immediately be corrected. An explanation of the relationship between wide gauge, minimum allowable flangeway gap, and the potential for flangeback impacts should be documented and briefed to maintenance staff.

Network Rail Company Standard RT/CE/S/103 should be revised to clarify the following: • Paragraph 4.4 as to how often track gauge in S&C is to be measured and by whom (ie basic inspector, supervisor or track engineer). • Paragraph 8.1.2 as to how often toe and heel openings are to be checked and by whom (ie basic inspector, supervisor or track engineer). • Paragraph 8.1.2 to prescribe where toe and heel opening should be measured in relation to the cross-section of the rails.

Network Rail Company Standard RT/CE/S/053 should be revised to remove ambiguity about whether the inspection required by paragraph 12 is to be undertaken at the same time as a detailed inspection or as part of the three-monthly/six-monthly inspection required by paragraph 7.

Consideration should be given as to whether there is a requirement for CE supervisors to inspect kicking straps during their inspections, and to whether such a requirement should be included in Network Rail Company Standard RT/CE/S/103.

Periodic monitoring procedures should be established to verify that basic visual inspections, as prescribed in RT/CE/S/103, have been carried out as recorded and signed for.

The planning, operating, and recording of basic visual inspection procedures, as prescribed in RT/CE/S/103, should be reviewed. Revised Track Inspection Sheets and Track Patrol procedure documents should be produced that: • Mandate the exact procedures that staff are required to follow. • Include instructions as to how recording and signing should be carried out, particularly in terms of recording the track in which staff walk, and the finding of no new or changed defects. • Include specific allowance for those stretches of line where the distance between tracks is greater than a standard ten-foot. If it is decided to continue using patrolmen in pairs, the recording and signing process for this method should also be prescribed.

Consideration should be given to enhancing the competence of CE patrolmen, by the provision of additional training, to enable them to recognise and report emerging problems such as loose nuts and off-centre threads on adjustable stretcher bars, during basic visual inspections.

Consideration should be given to the need for guidance to be included in training material, or in the Rule Book GE/RT8000, that specifies the width of ten-foot that is required to enable a person to stand in safety between two lines.

Reports of rough riding should be recorded systematically in order to ensure accuracy of response, and to allow the information recorded to be used to assist monitoring the condition of the infrastructure.

Consideration should be given to the use in future underbridge designs of steel fence construction rather than brickwork for filling gaps of the type found between the separate bridges at the Potters Bar site.

Consideration should be given to the reasonable practicability of securing OLE balance weights to reduce the risk of separation if they are struck during an accident.

Standards that prescribe strength requirements for body-to-bogie connections in vehicles should require that the potential modes of failure are determined at the design stage, and that action be taken to ensure that the integrity of the vehicle body structure is not compromised if the connection is overloaded.

The consequences of allowing the development, on a given axle, of an in-service wheel diameter difference which is considerably in excess of the limit imposed after reprofiling should be examined and, if appropriate, an in-service limit should be introduced.

The signallers at Kings Cross PSB should be provided with guidance to ensure that they have a clear understanding of the circumstances in which the signals-on control is to be used.

Consideration should be given to enhancing the training for RIOs to include additional guidance on priorities in the event of accidents and incidents where infrastructure failures are a predominant factor.

Network Rail should have in place adequate systems to ensure that the improvement actions listed in Section 8 are implemented effectively.