Initial investigations into the fatal rail crash in Wales last month have found that one train slid for around a kilometre before colliding with the other train, with a system that should have assisted adhesion blocked.
The collision took place on 21 October on the Cambrian line, approximately 900 metres west of a passing loop located at Talerddig, Powys.
At around 19:26 a (westbound) Transport for Wales (TfW) passenger service from Shrewsbury to Aberystwyth collided with a Machynlleth to Shrewsbury passenger service, also operated by TfW.
One passenger died and four other people were seriously injured. Eleven more people sustained injuries which required hospital treatment.
In an update, the Rail Accident Investigation Branch (RAIB) noted that both trains were fitted with wheel slide protection systems, ‘similar in function to anti-lock braking systems on road vehicles’, and an automatic sanding system that discharges sand automatically via sanding hoses when wheel slide is detected during braking and is intended to increase the friction at the wheel/rail interface.
The RAIB also pointed out that the Cambrian line is equipped with the European Rail Traffic Management System, a form of railway signalling.
The railway approaching Talerddig from each direction consists of a single track, with a loop to allow trains to pass each other, whereby trains enter a short length of adjacent track.
Westbound trains climb an ascending gradient to enter the loop and, on exiting, rejoin the single track as it descends.
The RAIB said its preliminary examination found that the westbound train had been due to stop in the loop to allow the eastbound train to pass and that initial analysis the on-train data recorder (OTDR) shows that the driver applied service braking to slow the train as it neared the loop.
Around 40 seconds after the first braking application, the OTDR records an emergency brake demand, which remained in place until the collision, with wheel slide starting during service braking and ‘constant during emergency braking’.
The westbound rain entered the loop, slowing but not stopping, rejoined the single line and continued for around 900 metres downhill, before colliding with the other train.
The RAIB said its measurements found low levels of wheel/rail adhesion levels at various locations from the approach to the loop to the point of collision.
An inspection of the automatic sanding system fitted to the westbound train showed that the sanding hoses on the leading vehicle of this train, which would have been active at the time of the accident, were blocked and apparently unable to discharge sand.
The RAIB said its investigation will seek to identify the sequence of events which led to the accident and consider other relevant factors.
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