Accidents

Cambrian Line Data Loss

Speed restriction data failed to be passed to trains, placing pedestrians on level crossings at risk.

In the United Kingdom, railway signalling is primarily implemented through trackside signals. In 2011, a trial  system was installed in the Machynlleth signalling control centre, which enabled suitably equipped trains  travelling over the part of the rail network that it controlled (the Cambrian lines) to acquire data relating to  speed restrictions and display these to the driver. The Cambrian lines are a collection of rail tracks which  run along the Welsh coast and as far inland as Shrewsbury. On 20th October 2017, a driver reported that  his train had failed to display speed restriction data.

The initiating event was just after 23:00 hrs on 19th October 2017, when a train automatically requested a  movement authority (permission to travel on a specified part of the rail network) which had already been  allocated to another train. This error condition is known to occur several times per year and causes an  automatic software reset to be invoked. A well established set of processes are used by the signalling  centre staff to return the rail system to normal operation. The staff followed their processes, and once the  system was functional, allowed the final three trains of the day to complete their journeys. On the following  day, it was the driver of the fourth train of the day who noticed the error and reported the failure.

Subsequent investigation revealed that speed restriction data had been unavailable since the software  reset, resulting in six trains completing their journeys without that data, before the driver of the seventh  train observed the problem.

The most significant risk identified thus far by the Rail Accident Investigation Board is that a number of the speed restrictions which were in place on the Cambrian lines had been invoked to allow pedestrians at  level crossings sufficient time to take action, when observing an approaching train. Luckily the failure did  not result in an accident — but this was due to luck, not failsafe systems on the railway.

This incident highlights the importance of the availability Data Property, as the data had been silently unavailable to trains. In addition, much of the digital audit trail relating to the failure was lost during  repeated attempts to correct the problem and get the rail network running again, a loss of the historyInter Data Property.

Links 

• Interim report: https://assets.publishing.service.gov.uk/media/5bc871d5e5274a0956564a41/  IR012018_181018_Cambrian_TSRs.pdf
  (accessed 31 December 2018).
• Final report: https://www.gov.uk/government/news/report-172019-loss-of-safety-critical-signalling-data-on-the-cambrian-coast-line (accessed14 January2020).