Deleted
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Post by Deleted on Aug 2, 2014 21:02:47 GMT
Today, my friend asked me why LU generally uses 2-aspect signals with repeaters, rather than simply cutting out the middle man and using 3-aspect signals. I started waffling about the low line speeds, the short distances between signals, the need for repeaters in tunnels with bends and curves and the general good braking distances of tube stock. However, I wasn't able to give a really neat, polished, complete answer. Obviously, out on the extremities of the Met 3- and 4-aspect signalling is used, where line speed is quite high and the signals are therefore quite far apart. Also, on the national rail tracks, obviously signalling is predominantly 3-aspect. But I was wondering if anybody on here could provide me with a more complete, more accurate answer as to why london underground employs (and has done for quite some time now) 2-aspect signalling on the majority of its manually operated railway. Thanks  |
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North End
Beneath Newington Causeway
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Post by North End on Aug 2, 2014 21:22:17 GMT
Today, my friend asked me why LU generally uses 2-aspect signals with repeaters, rather than simply cutting out the middle man and using 3-aspect signals. I started waffling about the low line speeds, the short distances between signals, the need for repeaters in tunnels with bends and curves and the general good braking distances of tube stock. However, I wasn't able to give a really neat, polished, complete answer. Obviously, out on the extremities of the Met 3- and 4-aspect signalling is used, where line speed is quite high and the signals are therefore quite far apart. Also, on the national rail tracks, obviously signalling is predominantly 3-aspect. But I was wondering if anybody on here could provide me with a more complete, more accurate answer as to why london underground employs (and has done for quite some time now) 2-aspect signalling on the majority of its manually operated railway. Thanks Basically, there's no need for anything different. Also, the green of a 3-aspect signal conveys a particular meaning, namely that the next signal is *not* red. Where signals are close together, for example in multi-home layouts, this wouldn't work as the distance between yellow and red would vary greatly between signals. Network Rail has 4-aspect signals on the Electric lines in to Liverpool Street which are more closely spaced than elsewhere, in order to get the required braking distances some of the sequences are arranged G YY YY Y R. On LUL, with signals even more closely spaced, trains would be forever running on yellows at certain times! |
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Deleted
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Post by Deleted on Aug 8, 2014 4:58:58 GMT
On LUL, with signals even more closely spaced, trains would be forever running on yellows at certain times! As opposed to running on reds as seems to be the case more often than not? Interestingly the New York subway uses 3 aspect signalling |
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roythebus
Pleased to say the restoration of BEA coach MLL738 is as complete as it can be, now restoring MLL721
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Post by roythebus on Sept 5, 2014 7:54:17 GMT
It works, it ain't broke, why try to fix it?
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Deleted
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Post by Deleted on Sept 5, 2014 18:34:48 GMT
Space in tube tunnels? 2 aspect signal is smaller.
I'll look in to it and see what the history books say.
I have a suspicion that roythebus is right though.
In the early days red/green was enough and its stayed that way since.
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