Practitioner viewpoint - October 2024

ON 5 OCTOBER 1999, 31 people lost their lives and a further 417 people were injured when two passenger trains collided head on at Ladbroke Grove just outside Paddington in central London. One of the trains had passed a signal at danger, a red traffic light, causing it to be on a collision course with an oncoming train. The combined speed on impact was approximately 130mph, causing significant damage to the carriages and a massive fire.

The resulting investigation identified multiple contributory factors, but the immediate cause was human error. The driver of one of the trains failed to acknowledge the red light ahead and to bring his train to a stop. In fact this wasn’t the first time that this had occurred. Worryingly there had been eight instances of trains passing this particular signal at danger in the six years preceding the incident, and this was also a fairly common occurrence right across the railway network.

A programme of work followed to fit mechanical protection at signals on the passenger train network which would activate and initiate emergency braking should a train pass the signal at danger. There was some controversy at the time, as this system, known as TPWS, did not completely prevent signals being passed at danger (SPADs). However it did significantly reduce the likelihood of a collision following a SPAD, it was readily available, affordable and could be fitted fairly swiftly across the network. It was initially seen as an interim solution, but is widely considered to have outperformed expectations, and remains the primary protection against collisions following SPADs even today. However TPWS was only fitted to the mainline passenger railway, signals on local lines and much of the freight network remain unprotected

The number of SPADs which occur on the UK railway remains pretty constant at around 300 per year. This sounds alarming, but when you normalise this by the number of trains, the miles travelled or the number of signals approached, the resulting number is actually tiny. Today, the UK is widely viewed as one of the safest in the world, but there is no doubt that potential still exists for a SPAD to result in a collision. So should more be done?

It’s always really difficult to build a business case for investment to address the risk of low likelihood, high impact events. The mitigation afforded by fitting of TPWS to the mainline passenger network has already significantly reduced the risk, expansion to cover the every signal on the railway or replacement with upgraded systems to prevent SPADs completely would come at significant cost to the taxpayer, and the question remains whether this investment is warranted by the level of residual risk remaining with TPWS in operation.

Safety professionals grapple with this risk ‘v’ cost balance on a daily basis. The better we get at safety, the harder it is to justify investment in ongoing improvement. What is ‘enough’ protection? Can any system ever be risk free? And how can we prevent human error resulting in catastrophic incidents? 

The debate goes on, and there is no ‘right’ answer. Anniversaries such as this serve as a timely reminder that we need to continue to learn and innovate to maintain proportionate management of risk in every sector.

Louise Ward is safety & sustainability director at G&W UK – Safety. For more information, visit www.gwrr.co.uk