RAIB investigates incident at Chalfont & Latimer last month

Footage from the Chiltern train’s CCTV system shows how close the two trains came to colliding

The Rail Accident Investigation Branch has disclosed that the driver of a Chiltern Railways service that almost collided with a London Underground train last month had passed a red signal and then reset the Train Protection and Warning System (TPWS) after it had triggered an emergency stop.

On the evening of June 21, the Chiltern service was travelling southbound on the Metropolitan line when it passed a red signal.

This signal was protecting a junction where the route had already been set for a Metropolitan line service to travel north, creating a conflicting crossing movement.

The RAIB investigation has discovered the Chiltern driver then reset the TPWS system when their train came to a halt around 300 metres beyond the signal. The train then continued towards Chalfont & Latimer station, around 600 metres away.

As a result of the position of the points at the junction, its route towards the station took it onto the northbound line. The northbound London Underground train on this line was stationary because the signal in front of it had changed to red as a result of the southbound train passing the red signal. The two trains stopped just 23 metres apart.

There were no reported injuries but some track components were damaged as the southbound train had proceeded through a route that was not set for it.

The RAIB says its investigation will identify the sequence of events which led to the signal being passed at danger and the subsequent near-miss. It will also consider:

  • The actions of the people involved;
  • Chiltern Railways’ arrangements regarding the training, competence and fitness of its train drivers;
  • Chiltern Railways’ management of risk associated with its drivers operating on the London Underground network;
  • How risk associated with signals passed at danger by non-London Underground trains is managed on the London Underground network; and
  • Any relevant underlying factors.

“We will publish our findings, including any recommendations to improve safety, at the conclusion of our investigation,” RAIB added.

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