An avoidable accident

 - and an environmental catastrophe narrowly and expensively avoided.

The report into the Llangennech derailment has been published, and it makes depressing reading. Not only does it highlight poor maintenance:

The derailment occurred because one set of wheels on the third wagon in the train stopped rotating during the journey. The wheelset had become locked, probably because of a defect in the braking system on the third wagon, arising from deficiencies in the design and maintenance of components. The sliding of the locked wheel along the railhead caused damage to the profile of the wheel treads. This meant that the wheels were unable to safely negotiate Morlais Junction, near Llangennech, damaging the pointwork and causing the third wagon to become derailed. The following wagons derailed on the damaged track. Some of the derailed tank wagons were ruptured in the accident, and the spilling fuel ignited.

- but also points out that technology (hot axle box detection) was able to detect the trouble when the train passed through Pembrey station. However, it seems that the reporting software had been disabled because there had been false positives in the past.

Had the wheelset detection technology within the Pembrey HABD system been connected and capable of identifying and discriminating between the two conditions, it would have been capable of triggering an alarm. The distance to the next junction, and the speed of the train involved in the accident, means that there would have been time, after the train passed Pembrey HABD, for the signaller or control room to have been alerted and the train stopped before the damaged wheelset was able to cause a derailment. Since this is likely to have prevented the accident from occurring it is considered to be a probable causal factor.

The details of the report incidentally expose how much the railway system has become compartmentalised since its privatisation under the Major government. This does not seem to be a large factor in the Llangennech report, where all the companies involved are thanked for their cooperation, but it surely cannot help.