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Post by edwardfox on Feb 8, 2011 23:23:47 GMT
At LU stations, the signal changes to red while the departing train is still only halfway out of the station. This seems to be the normal thing.
I have noticed on one or two shared stations on the DC line that it takes a full 8-10 seconds from the back end of the departing train passing the signal for it to change from green to red. I was thinking this could be potentially dangerous in conditions of severe fog
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Deleted
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Post by Deleted on Feb 8, 2011 23:57:17 GMT
No danger. The signal behind will not go green until this signal goes red.
The actual signalling system design is probably more complex, but this is the essential point.
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Post by 21146 on Feb 9, 2011 0:00:35 GMT
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Post by edwardfox on Feb 9, 2011 0:06:19 GMT
Exactly, although the train was a little further away when the signal finally changed. |
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Colin
Advisor
My preserved fire engine!
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Post by Colin on Feb 9, 2011 1:11:29 GMT
If you stand at the bridge outside Wimbledon Park you'll see exactly the same effect with C & D stocks on the up/eastbound. This is quite normal on Network Rail metals and it's because they have fixed overlaps at 183 metres whereas LU uses calculated overlaps and replacement block joints at signals. Have a look at this thread and let us know if it answers your nagging doubts about the safety of signalling..... |
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Deleted
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Post by Deleted on Feb 9, 2011 1:40:20 GMT
ooo the 183m is a bit of a generalisation - But the 'standard' is 200 yds or 183m in european.
With automatic signals, such as those found on the DC Lines out of Euston each signal usually will only have 1 TC (track circuit), which covers both the berth and the overlap. As automatic signals are operated purely on occupation of track circuits (the signaller can elect to hold one at red individually, if the signal is so equipped) It won't fall back to red until the next TC after the overlap is occupied, and as this is ~183m from the signal the train will often be out of sight before it reaches this point. But you can rest assured as the previous signal will also be being held at red until the train clears the TC.
If you want to see it in operation in context, take a look at Wembley Suburban Simsig - it covers the DC Lines and you can see the operation of the signals in relation to the Track Circuits.
HTH
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Deleted
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Post by Deleted on Feb 9, 2011 9:49:20 GMT
On LU it is considered 'dangerous' to show anything other than the most restrictive aspect to the rear of a train. Some overlaps on the higher speed sections of lines will be greater than a train's length, hence you could show a green aspect behind a train. Repeater signals also have a replacement track circuit, unless they are part of a stop signal arrangement. This is because of the 2-minute rule, with trainstops; it's to give maximum safety whilst working under SCAT.
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