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Post by mandgc on Feb 17, 2006 8:46:02 GMT
I have been looking through some recent posts and it seems that over the years the 'X Signal' now serves a number of purposes.
I believe it was originally used to prevent a train from passing an Auto. signal in rear of a Controlled (Semi Automatic) signal where there was a risk of the train backlocking the Controlled signal. It now appears to be used at certain Platform Starting signals to hold the train for various reasons.
How are these Starting signals controlled and for what purpose are they used ?
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Post by c5 on Feb 17, 2006 9:32:12 GMT
The X signals for at both Paddingtons on the SSR are controlled by the Edgware Road signalman. There are switches used that simply put the signal back to danger. They are used if you need to contact a train operator, though trains shouldn't be held there for topo long, as trains will block back behind, in the tunnel - something to avoid.
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Deleted
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Post by Deleted on Feb 17, 2006 12:41:05 GMT
The original reason for X signals was due to the primitive nature of lock releasing on old signal frames in use on the Underground - instead of individual releases being able to release part of a backlocked route, there was only a single global release that released all of the routes, thus bringing the whole site to a stand and livelocking the entire frame for the release timeout.
Nowadays they are of course used for all sorts of fascinating things: station starters, gauging alarms, floodgates, etc...
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Colin
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Post by Colin on Feb 17, 2006 12:48:09 GMT
Essentially, the whole point of an X signal is to prevent a driver from adopting the 'stop and proceed' rule - not just on the approach to controlled areas, but also for possesions and floodgates.
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Deleted
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Post by Deleted on Feb 17, 2006 17:07:47 GMT
Plus there are anomalies like ECX691...
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Post by mandgc on Feb 18, 2006 23:09:57 GMT
London Bridge and Waterloo were, I think, mentioned as having X Signals. What is the reason for having them there?
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towerman
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Post by towerman on Feb 19, 2006 1:32:12 GMT
I think there were floodgates at Waterloo and London Bridge was a controlled area as it had an crossover before the modernisation.
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