An infrastructure monitoring train stopped at the marker marking the end of its movement authority, despite its onboard equipment telling the driver it could travel another 610 metres. The safety system failure happened near Welshpool in Powys on 15 September 2026. The Rail Accident Investigation Branch (RAIB) published its preliminary findings on 21 October.
According to RAIB’s statement, the onboard European Train Control System (ETCS) used incorrect wheel diameter information to calculate the train’s position. The branch identified potential weaknesses in the system’s safeguards which it says should be considered as part of Network Rail’s investigation.
The train stopped in the right place, but the display was wrong
The train was operating under ETCS Level 2 supervision. A movement authority defines how far a train is permitted to travel. In this case, the train reached the marker indicating that limit and stopped there, while the onboard display suggested the limit was still 610 metres ahead. The statement describes a safety system failure, not a collision or derailment.
Examination after the incident found that a component of the onboard ETCS had prevented the correct wheel diameter from being recorded following routine maintenance. The system therefore used an incorrect value when calculating the train’s position. RAIB said neither the independent speed measurement system nor the track-mounted balises — devices that transmit information to passing trains — effectively corrected the resulting distance error.
RAIB refers its findings to Network Rail
RAIB has decided not to carry out a full investigation into the incident. It has, however, written to Network Rail, Britain’s railway infrastructure manager, highlighting potential weaknesses in the onboard ETCS safeguards for consideration during its investigation. Copies of the letter were also sent to the rail regulator, the Office of Rail and Road, and the operator of the infrastructure monitoring train.
The published findings come from RAIB’s preliminary examination, rather than a final investigation report. The statement does not set out the outcome of Network Rail’s investigation or confirm that technical changes have been introduced. It also does not establish that the same fault affects all ETCS equipment.
