Wrong side failure near Welshpool

At around 23:52 on 15 September 2026, a wrong side failure of the European Train Control System (ETCS) occurred near Welshpool, Powys.

RAIB’s preliminary examination into this incident found that an infrastructure monitoring train operating under Level 2 ETCS supervision stopped at the block marker which should have signified the end of its movement authority. However, despite having reached the block marker, the signalling equipment on the train indicated to the driver that there remained 610 metres further to travel before the end of the movement authority was reached. This error was attributed to the on-board ETCS equipment using incorrect wheel diameter information to calculate the train’s position.

Post-incident examination identified a component part of the on-board ETCS equipment had prevented the correct wheel diameter from being stored following routine maintenance to the train. An independent speed measurement system on the train is intended to supplement the distances generated by the wheel diameter to achieve the necessary accuracy. Track-mounted balises are also intended to reset the distance on the train, should inaccuracies occur. However, neither of these systems proved effective at correcting the inaccurate distance which was generated in this instance.

RAIB has previously investigated issues with the integrity of the ETCS system on the Cambrian lines, including an investigation into the loss of safety‑critical data (RAIB report 17/2019). In that instance, RAIB identified that a support system had caused a failure of the higher integrity signalling system and that appropriate protection against foreseeable failures had not been provided.