Case Study: Defective On-Train Equipment
Following a proposal to review the Rule Book, standard and associated guidance for operation of trains following use of the emergency bypass switch (EBS), TOMSC decided to extend the scope of the review to include the Automatic Warning System (AWS), Driver’s Safety Device (DSD) (and vigilance) and the Train Protection and Warning System (TPWS).
Using a similar risk review process to that which had recently been used to determine the arrangements for defective GSM-R, data from the Safety Risk Model and SMIS was used to assess the safety risk associated with different responses to defective on-train equipment. The initial results were reviewed and refined through a series of five risk analysis workshops with industry representatives.
For AWS, DSD and TPWS defects our work reached the same conclusion. While permission would still need to be sought from the train’s operator to facilitate decisions about the most effective means of having the train repaired, the total network risks could be minimised by allowing passengers to remain on the train for up to 100 miles and at a maximum speed of 60 mph rather than 40 mph. This recommendation was made because the resulting risk to the failed train (travelling up to 100 miles) – and to other trains on the network – is less than the secondary risks associated with passengers alighting from the defective train and joining another. With defective AWS and DSD, the higher speed allows the maximum protection from the overspeed element of TPWS to be retained.
For freight trains the maximum travelling speed with AWS, DSD and TPWS defects was changed to 50 mph following industry feedback. Industry representatives felt that 60 mph could cause additional risks for class 6 freight trains (for which 60 mph is their normal maximum speed) and at 50 mph freight trains retain the same level of TPWS protection as passenger trains do at 60 mph.
During the review there was also an aspiration from the Rail Delivery Group (RDG) to raise the present 100 mph limit for a train on which the pantograph automatic dropping device (ADD) has been isolated. RSSB’s initial view was that with the ADD isolated, a device that is meant to minimise damage to infrastructure and train in the event of an OLE defect being encountered was no longer available, so the limit of 100 mph might be too great. There was not sufficient data to come to any definitive view either way and so no change is being made. However, we have provided additional guidance that train operators may wish to impose a speed lower than 100 mph where the type of train is known to be susceptible to dewirement or where the OLE is supported by headspan construction. Any failure of the latter affects all lines at that location.
Finally, as part of the work, we revised the defective door instructions. This was done to reflect the fact that many new trains are now, internally, effectively a continuous tube, with little or no ability to secure individual vehicles out of passenger use. Consequently, the revised arrangements consider the effect of a defective door on the train as a whole and the distance an individual passenger might now be from an available emergency exit.
Together, these findings have been reflected in:
- Changes to Rule Book (GERT8000) modules TW5 and AC
- RIS-3437-TOM Defective On-Train Equipment, issue 2 which incorporates guidance previously shown in its separate guidance note GOGN3637.
These changes will be published in the September Standards Catalogue and will come into operation in December 2018.
Once fully implemented in train operators’ contingency plans, the revised arrangements are likely to reduce the number of passenger trains terminated short of their destinations and reduce overall network delays, while not adversely affecting safety risk.