HomeGovernanceAccident InvestigationRAIB reports on SPAD and near miss at Chalfont & Latimer station

RAIB reports on SPAD and near miss at Chalfont & Latimer station


The Rail Accident Investigation Branch (RAIB) has released its report into a signal passed at danger and subsequent near miss that occurred on 21 June 2020 at Chalfont & Latimer station on London Underground’s Metropolitan line.

At around 21:43, a southbound Chiltern Railways train passed a signal displaying a red (stop) aspect (a signal passed at danger or a ‘SPAD’). This resulted in the train being automatically stopped by the ‘tripcock’ safety system, which had applied the train’s emergency brake.

Without seeking the authority required from the service operator (signaller), the driver reset the tripcock before continuing towards Chalfont & Latimer station, where the train was routed towards the northbound platform, which was already occupied by a London Underground train.

On approaching the station, the Chiltern Railways train was routed to the right into the path of the London Underground train.

The Chiltern Railways train stopped about 23 metres before reaching the other train, which was stationary. There were no reported injuries, but there was minor damage to signalling equipment and a set of points.

RAIB’s investigation concluded that the probable cause of the SPAD was that the driver of the Chiltern Railways train was fatigued. The driver stated that he decided to proceed without authority because he did not recall passing the stop signal and believed the tripcock safety system activation had been spurious. This decision may also have been affected by fatigue.

The Chiltern train halted just 23 metres from the stationary London Underground train.

RAIB found that Chiltern Railways’ processes for training and testing a driver’s knowledge of what to do following a tripcock activation were not effective. A probable underlying factor was that Chiltern Railways’ driver management processes did not effectively manage safety-related risk associated with the driver involved in the incident. It is possible that this was a consequence of a high turnover of driver managers, insufficient driver managers in post and their high workload.

Although not causes of the incident, RAIB also found shortcomings in other aspects of these driver management processes, and in risk management at the interface between Chiltern Railways and London Underground.


As a result of its investigation, RAIB has made three recommendations and identified one learning point.

The first recommends that Chiltern Railways improves its driver management processes. The second recommends that Chiltern Railways and London Underground jointly establish an effective process for the management of safety at the interfaces between their respective operations. The third recommends that Chiltern Railways, assisted by London Underground, reviews the risk associated with resetting train protection equipment applicable to Chiltern Railways’ trains on London Underground infrastructure.

The learning point concerns the importance of considering sleep disorders during routine medical examinations of safety critical workers.


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