Collision of passenger trains at Talerddig, Powys, Wales

At around 19:26 on the evening of 21 October 2024, train 1J25, the 18:31 Transport for Wales (TfW) passenger service from Shrewsbury to Aberystwyth, collided with train 1S71, the 19:09 Machynlleth to Shrewsbury passenger service, also operated by TfW. The trains collided approximately 800 metres west of the passing loop located at Talerddig, Powys on Network Rail’s Cambrian line.
Very sadly, one passenger died and four other people were seriously injured. Eleven more people sustained injuries which required hospital treatment.

In addition to emergency services carrying out rescue operations, British Transport Police, the Office of Road and Rail (ORR) and the Rail Accident Investigation Branch (RAIB) have commenced investigations. This note is based on bulletins issued by RAIB.
On the day after the collision, RAIB issued a statement reporting that its “…initial inspection of the track on approach to the point of collision found evidence that wheel/rail adhesion was relatively low, suggesting that the train may have entered into wheel slide when braking.”

On 5 November 2024, RAIB issued an update following its examination of the site and the trains involved. The trains were both two-car Class 158 diesel multiple units. These units are equipped with wheel slide protection systems and fixed rate automatic sanding systems, which discharges sand to the track when wheel slide is detected during braking, a system which aims to increase the available friction at the wheel/rail interface in poor adhesion conditions.

The railway approaching Talerddig from each direction consists of a single track. At Talerddig itself, there is a passing loop. Eastbound and westbound trains were timed to pass each other, stopping in the loop if necessary. Westbound trains climb an ascending gradient to enter the loop and, on exiting, rejoin the single track as it descends towards Llanbrynmair and Machynlleth.

The Cambrian line is equipped with the European Train Control System (ETCS), the signalling and train protection sub system of the European Rail Traffic Management System. This system has no lineside signals and transmits speed and movement authority into the train, displayed to the driver alongside the train’s speedometer. The limits of each section of track controlled by the system are signified by reflective lineside signs known as block markers. The train driver’s display would show if a train were required to stop at a block marker. The block marker itself acts as an absolute position location and back up in the event of a failure.

RAIB’s preliminary examination has found that westbound train 1J25 had been due to stop in the loop at Talerddig to allow eastbound train 1S71 to pass. Initial analysis of data from 1J25’s on-train data recorder (OTDR) showed that the driver applied service braking to slow the train as it neared the loop at Talerddig. Around 40 seconds after the first service brake application, the OTDR records an emergency brake demand being made. This emergency brake demand remained in place until the collision. OTDR data shows that wheel slide started during service braking and was constant during emergency braking.

Train 1J25 entered the loop at Talerddig and, although it slowed while passing through the loop, it did not stop before passing the block marker positioned near the exit. The train left the loop, rejoined the single line, and continued to travel for approximately 900 metres on the descending gradient, before colliding with train 1S71.

RAIB reported that there is conflicting evidence relating to the speed of the trains at the point of collision. Initial analysis indicates that train 1J25 was travelling at between 24km/h (15mph) and 39km/h (24 mph), while train 1S71 was travelling at around 10km/h (6mph) in the opposite direction (a closing speed of up to 49km/h (31mph). RAIB is continuing to analyse evidence relating to the collision speed.

Building on the earlier statement, having carried out measurements of wheel/rail adhesion levels at various locations from the approach to Talerddig loop to the point of collision, RAIB reported that levels of wheel/rail adhesion were low.

In addition, RAIB’s inspection of the automatic sanding system fitted to train 1J25 after the accident showed that the sanding hoses of the active sanders on the leading vehicle of this train were blocked and apparently unable to discharge sand.

It would be wrong to assume that the collision was caused simply by poor adhesion and blocked sander hoses. These may well be the immediate causes, but, as was seen from RAIB’s exhaustive investigation into the collision at Salisbury in 2021, there are likely to be many causal and contributory factors. The circumstances of both collisions appear to be superficially similar, but we will have to await RAIB’s report to understand all the factors that led to this tragic event.

Image credit: iStockphoto.com/ChrisHepburn