Rail safety concerns raised after signalling failure near Welshpool

Rail safety investigators have raised concerns after a train near Welshpool was incorrectly told it could travel another 610 metres when it had already reached the end of its permitted route.

The incident happened at around 11.52pm on September 15, when a specialist train used to monitor railway infrastructure experienced a signalling failure.

The Rail Accident Investigation Branch (RAIB) has revealed that the train had stopped at a marker indicating the end of the distance it was authorised to travel.

However, the signalling system inside the driver’s cab incorrectly showed that the train could continue for another 610 metres.

Investigators traced the problem to incorrect information about the diameter of the train's wheels, which was being used by its computerised signalling equipment to calculate its position.

The train was operating under the European Train Control System (ETCS), a modern signalling system designed to monitor train movements and help prevent accidents.

Unlike traditional railway signalling, ETCS provides information directly to drivers through equipment inside the train’s cab.

Investigators discovered that a faulty component had prevented the correct wheel measurements from being saved following routine maintenance.

This meant the train’s computer was calculating how far it had travelled using inaccurate information.

More concerningly, two separate safety systems designed to correct such errors also failed to resolve the problem.

One uses independent speed measurements to help calculate the distance travelled, while the other relies on electronic devices installed along the railway track to update the train's position.

Neither system successfully corrected the inaccurate reading.

The RAIB described the incident as a “wrong side failure”, a railway term used when signalling equipment fails in a way that could compromise safety rather than automatically protecting against danger.

Although the incident did not result in an accident or near miss, investigators believe it has highlighted potential weaknesses in the safety arrangements of the signalling equipment.

The RAIB has previously investigated problems involving the ETCS system on the Cambrian railway lines, including a 2019 report concerning the loss of safety-critical signalling information.

That investigation identified weaknesses in the protection provided against certain equipment failures.

Following its initial examination of the latest incident, the RAIB has decided not to launch a full investigation.

However, it has written to Network Rail urging it to examine the potential weaknesses identified in the train’s signalling equipment as part of its own investigation.

The rail safety watchdog has also sent copies of its findings to the Office of Rail and Road, which regulates railway safety, and the operator of the monitoring train.

While no accident occurred, the incident has raised questions about why several layers of technology designed to ensure trains know their precise location failed to prevent such a significant error.

We have contacted Network Rail for comment.

What is a wrong-side signalling failure? 

A wrong-side signalling failure is described by the industry as a dangerous railway system malfunction where the equipment fails into an unsafe state - such as showing a false clear or green/proceed aspect when the track is actually occupied, obstructed, or broken.

Unlike standard right-side failures (where a system breaks safely by defaulting to a red ‘stop or danger aspect and causing delays), a wrong-side failure removes the safety protections meant to keep trains from colliding or derailing.