Delayed rail treatment train likely cause of Salisbury collision

RAIB’s interim report finds rail treatment was delayed due to engineering work.

THE Rail Accident Investigation Branch has published an interim report about the cause of a collision between two passenger trains on the outskirts of Salisbury on October 31, 2021.

The services concerned were the 1L53 17.20 hours London WaterlooHoniton and the 1F30 17.08 hours Portsmouth Harbour-Bristol Temple Meads which collided at Salisbury Tunnel Junction where the lines on which they were travelling converged.

The route had been set and signals cleared for 1F30, a four-car train made up of two Class 158 units, with the junction being protected by the signalling system controlled from Salisbury Signalbox, but 1L53, a three-car Class 159 set, passed the protecting stop signal SY31 at danger.

The on-train data recorder (OTDR) showed that after leaving Andover the train from Waterloo accelerated to the permitted line speed of 90mph and continued at this speed until power was cut off for the falling gradient as Salisbury was approached. An

AWS warning was acknowledged as a double yellow was displayed at signal SY29R, indicating that the route was not clear to reach the station.

After passing the double yellow a brake application was made with the intention of being able to stop at the signal protecting the junction which was a little under a mile away. It was immediately evident that the wheels were sliding and although the wheel slip/slide prevention system was operating, speed reduced only slowly.

As the stop signal SY31 was approached, the Train Protection and Warning System detected there was an over speed above the required 34.5mph and this instituted an emergency brake application which had no effect, as it had already been applied by the driver. As a result, the train was travelling at 52mph when the collision occurred at the junction with 1F30, which was travelling at 20mph.

The weather on the day in the area had featured strong winds and heavy rain and the railhead was wet and, in addition, there was found to be a deposit of crushed leaf material which resulted in low friction that compromised braking.

Network Rail has procedures for the management of low adhesion risk using railhead treatment trains (RHTT), and in the area concerned the process was for the track to be treated by a Multi Purpose Vehicle providing high pressure water jetting and a gel that is intended to break up any remaining leaf film on the railhead once every 24 hours.

On the day in question the track was due to be treated by an RHTT before the time the accident occurred but this had been put back because of planned engineering work, which meant that the interval for treatment was extended to 36 hours as it had been rescheduled to take place at approximately 23.00.

The final report from the RAIB will look in more detail at the train braking characteristics, the processes when trains are operating in situations where there could be low rail adhesion and the management of risk by Network Rail covering the regulation of trains at high-risk locations and vegetation control.