Post by railtechnician on Sept 17, 2013 8:20:24 GMT
Sept 16, 2013 22:24:19 GMT @amershamfast said:
I have explained why it is necessary to have a fixed point! As things are and as the event was explained a train was sent towards the single track section trapping the train that was already in the section. Think of the track as a wishbone, one road in and the other road out with the points at the junction of the two, when a train is too close to the points on the in road it fouls the out road because there is not room for a train to pass or as in this particular case locked the points. Thus an exceptional move (setting back) had to be made to free the points.
Proper signalling would have halted the approaching train before it trapped the one in the platform.
As long as the TBTC system knows that it must not route a train towards Mill Hill East if one is already on the branch, and that the operator may only initiate such a move after confirming their intention then it is simply not an issue IMHO and I'm yet to be dissuaded from that view.
In an ideal world there would never be a need for exceptional moves and IMHO upgrading signalling is about working towards that goal by continued improvement.
Using your logic there was never a need to spend vast amounts of money on SPAD mitigation because LT signalling was intrinsically safe. Had such existed before 1975 Moorgate would not have happened. Just because TBTC appears to be safe does not make it so and most catastrophes on the system are the result of a chain of failure. In the Mill Hill event the action of the signaller is a single failure, but if something else were to fail you could end up with a collision. Of course the devil is in the detail but there is always a need for continued improvement as opposed to blind complacency.