ABSTRACT
In the absence of a train protection system, signals passed at danger (SPADs) ie when a train passes a red signal, would be one of the main contributors to train accident risk on UK railways. The major train accident at Ladbroke Grove in 1999, inwhich 31 peoplewere killed, was due to a signal passed at danger and a subsequent head on collision between a suburban passenger train and a high speed passenger train. Following Ladbroke Grove there was a public inquiry into the accident. One of many recommendations made by the head of the investigation, Lord Cullen, was to roll out the Train Protection and Warning System (TPWS) across the UK rail network (Cullen, 2001). If TPWS had been installed at the signal that was passed at danger at Ladbroke Grove, the collision would have been avoided. The TPWS acts to:
1) Initiate a brake application on a train that approaches a signal showing a danger aspect at excessive speed, and
2) Initiate a brake application on a train that passes a signal at danger without authority from the signaller.
