The UK Rail Accident Investigation Branch has published its preliminary findings concerning a railway signalling incident near Welshpool on 15 September.
A monitoring train reached the marker at which its authority to move should have ended, but its onboard European Train Control System incorrectly indicated that it could continue for another 610 metres.
Investigators linked the discrepancy to incorrect wheel-diameter information used to calculate the train’s position.
Other systems intended to correct positioning errors did not resolve the problem.
RAIB will not conduct a full investigation but has formally highlighted the safety implications to Network Rail and notified the Office of Rail and Road.
Why it matters: The Cambrian lines depend on digital train-control technology. The incident raises important questions about safety-critical software, maintenance procedures and the resilience of the signalling system.
Status: A confirmed technical safety failure; not a collision or a confirmed near miss.
