Lack of adhesion between the wheels of a Virgin train and the track caused it to crash into the buffers at Chester Railway Station.
This is the preliminary finding of an investigation by the Rail Accident Investigation Branch (RAIB) into the November 20 incident which left two passengers slightly injured.
The RAIB’s full investigation will examine the train’s braking system, adhesion conditions at the time and the condition of the rails.
An initial report says the 10.10am service from London Euston to Chester was approaching the station when the driver applied the brakes to reduce the speed in line with the 20mph speed limit into the platforms.
The weather had been dry but a rain shower was just starting and the RAIB says “adhesion between the wheels and rails was reduced”.
The report adds: “The train’s wheel slide protection system detected the wheels were sliding on the rails, regulated the application of the brakes, and the train was able to achieve a rate of deceleration sufficient to bring its speed down to within the speed limit as it approached the station.
“As the train approached the platform the driver lightly applied the brakes again but the wheels immediately started to slide. Despite the immediate automatic activation of the wheel slide protection system, the train’s deceleration was insufficient to bring it down to a safe speed as it moved along the platform.
“Consequently, the emergency brakes were applied by train protection and warning system and the driver pressed the emergency stop button very shortly afterwards. The combination of emergency braking and the detection of wheel slide triggered the automatic sanding system on the leading vehicle to drop sand onto the rail head.
“The presence of the sand improved adhesion for the wheels that ran over it and the speed was reduced before the train collided with the buffer stop at the end of the platform.”
The RAIB says the old-style buffer stop had only minimal capacity to absorb energy and was destroyed by train which mounted the platform.
Investigators will look at similar events; notably a series of low adhesion events in autumn 2005.
RAIB’s inquiry is independent of any investigation by the Office of Rail Regulation. It will publish its findings, including any recommendations to improve safety.