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Post by dave1 on Jul 6, 2016 6:56:41 GMT
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Post by Nortube on Jul 6, 2016 9:54:34 GMT
A1004 is an example of a four digit auto draw-up. It is the only one that I can think of on the Northern line and is a relatively new thing. It is a draw-up for Mill Hill East, added as part of the terminal protection arrangements. Despite being near the end of a long stretch of straight track and this clearly visible, it also had a fixed yellow repeater - R1004. A1004 is the only NB running signal between Finchley Central and MHE. A1004 has a 4.5 second timer (20mph). An 18mph policemen was also added just over halfway down the platform. I think the policeman was added first in 1976 as initial protection after Moorgate and A1004 was added later in 1980. A1004 was a PITA. Because it was clearly visible from a long way away, the reaction was to slow down for it sooner than necessary, especially at night. Alternatively, sometimes drivers left it too late to slow down and consequently SPADded it. The addition of A1004 spoilt what used to be a good run to MHE, although of course it served the purpose of ensuring the train slowed down for the platform. Any references to Northern line signalling in my posts refers to when there were actually signals on the Northern line
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Post by railtechnician on Jul 7, 2016 2:52:15 GMT
A1004 is an example of a four digit auto draw-up. It is the only one that I can think of on the Northern line and is a relatively new thing. It is a draw-up for Mill Hill East, added as part of the terminal protection arrangements. Despite being near the end of a long stretch of straight track and this clearly visible, it also had a fixed yellow repeater - R1004. A1004 is the only NB running signal between Finchley Central and MHE. A1004 has a 4.5 second timer (20mph). An 18mph policemen was also added just over halfway down the platform. I think the policeman was added first in 1976 as initial protection after Moorgate and A1004 was added later in 1980. A1004 was a PITA. Because it was clearly visible from a long way away, the reaction was to slow down for it sooner than necessary, especially at night. Alternatively, sometimes drivers left it too late to slow down and consequently SPADded it. The addition of A1004 spoilt what used to be a good run to MHE, although of course it served the purpose of ensuring the train slowed down for the platform. Any references to Northern line signalling in my posts refers to when there were actually signals on the Northern line It is usual to suppress a red signal when it can clearly be seen well in rear of its sighting point, such a suppressed red exists in the T4 loop on a very long straight section of tunnel, you can just imagine how the headway would be extended and thus impacting the timetable were it not suppressed. Perhaps MHE being a terminal site made it more of a special case in terms of TETS safety, the fact that the signal has a repeater re-inforces that idea.
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Post by railtechnician on Jul 7, 2016 3:23:22 GMT
Thanks everyone I am learning some more about signalling. I have the diagram for my original question. So it looks as though A 4011 is an auto draw up signal allowing trains to pass at 30 mph or less. It would be interesting to see exactly how the note denoted by the asterisk at A395, 30MPH sign and A4011/R395 is worded. I note that no overlap is shown for A4011 and that there is little more than a train's length between A4011 and A395 and also that A395 is situated far enough in rear of the Regent's Park platform for a train tripped at 30mph to come to an emergency stop before reaching it. The way I see it a driver approaching A4011 with a train berthed in Regent's Park platform would have to see a red signal. Providing the train approached at 30 MPH or less passing the speed limit sign would change from red to green and yellow as a draw up, otherwise I expect the train would come to a halt and have to wait 4.5 seconds for a time relay to wind up before seeing the draw up green and yellow.
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Post by Ivory Tower on Jul 7, 2016 6:54:00 GMT
The asterisk denotes existing equipment. I don't think that A4011 is a draw up signal as the signal has to be clear to enable BM5 to clear and therefore a driver will never normally see it at danger. The only time a driver will see it at danger would be if he was authorised to leave Baker St under rule. The signal only has 2 aspects red/green.
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Post by Nortube on Jul 7, 2016 16:32:21 GMT
I noticed that A4011 doesn't have an overlap which, to me is another reason to suspect it serves no purpose as a running signal in the normal sense of things. There is no timer section with it either, so it's not a speed-controlled type signal. One interesting thing is that the overlap for B5 is 190m, whereas B2 route 2 (SB Jubilee starter to Bakerloo line) overlap is 748m, ending at the same place as the end of the overlap for A395. This means that a train coming from the Jubilee line would still be in the overlap until it had almost berthed in Regent St platform.I assume that the reason for such a long overlap is to do with trains transferring from one line to another. As I had to go into the loft, I thought I'd look for How the Underground works. The print is yellow on an olive background (not green as I frst thought), although I suppose it could look grey in a different light. The scan below appears to be a bit brighter (on my monitor) than the colours actually are. The date is 1968
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Post by railtechnician on Jul 8, 2016 13:28:26 GMT
The asterisk denotes existing equipment. I don't think that A4011 is a draw up signal as the signal has to be clear to enable BM5 to clear and therefore a driver will never normally see it at danger. The only time a driver will see it at danger would be if he was authorised to leave Baker St under rule. The signal only has 2 aspects red/green. As I said auto draw up signals are rare and I have never seen a circuit for one nor seen one in situ as far as I recall. Thus I had no way of knowing for sure if such would be a 3 aspect signal. It was only supposition and I was already aware that the driver of an approaching train would normally never see a red. For some reason we got off the idea that it was a 'round the bender' signal. Clearly it is a 'round the bender' signal.
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Post by railtechnician on Jul 8, 2016 13:31:45 GMT
I noticed that A4011 doesn't have an overlap which, to me is another reason to suspect it serves no purpose as a running signal in the normal sense of things. There is no timer section with it either, so it's not a speed-controlled type signal. One interesting thing is that the overlap for B5 is 190m, whereas B2 route 2 (SB Jubilee starter to Bakerloo line) overlap is 748m, ending at the same place as the end of the overlap for A395. This means that a train coming from the Jubilee line would still be in the overlap until it had almost berthed in Regent St platform.I assume that the reason for such a long overlap is to do with trains transferring from one line to another. As I had to go into the loft, I thought I'd look for How the Underground works. The print is yellow on an olive background (not green as I frst thought), although I suppose it could look grey in a different light. The scan below appears to be a bit brighter (on my monitor) than the colours actually are. The date is 1968 Your copy is identical to mine, grey/yellow !
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Post by dave1 on Jul 8, 2016 13:49:11 GMT
The asterisk denotes existing equipment. I don't think that A4011 is a draw up signal as the signal has to be clear to enable BM5 to clear and therefore a driver will never normally see it at danger. The only time a driver will see it at danger would be if he was authorised to leave Baker St under rule. The signal only has 2 aspects red/green. As I said auto draw up signals are rare and I have never seen a circuit for one nor seen one in situ as far as I recall. Thus I had no way of knowing for sure if such would be a 3 aspect signal. It was only supposition and I was already aware that the driver of an approaching train would normally never see a red. For some reason we got off the idea that it was a 'round the bender' signal. Clearly it is a 'round the bender' signal. We did go off the idea of a round the bend signal but that now makes me think why did they put such a signal in all those years after Stratford and resignalling was in 1977, why not just a normal numbered signal. After all as has been said no one will see it at red.
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Post by railtechnician on Jul 9, 2016 2:28:05 GMT
It was obviously a signalling standard to install a round-the-bend signal at the time (indeed they were installed on the west end of the Picc around the same time, there being quite a few between Hounslow West and Hatton Cross) the year such were added to signalling standards is somewhat irrelevant in terms of a subsequent installation, signalling evolves over time and the current standards at the time are what any resignalling is based upon. AFAIK round-the-bender signals would still be a standard for new work in terms of 'standard' LT signalling today if such were still being installed. I have no idea what signalling standards were applied when the Central line was resignalled but there would be many detail differences as it was not standard LT signalling. Underlying signalling principles will be much the same all over the world but the standards appropriate to any given signalling system will determine what functions are required and what equipment is necessary to achieve them. For my part I am scratching my head with regard to the removal of delta BL and no replacement, then again perhaps the renumbering of tracks and the new signalling layout enabled the dropping and subsequent pickup of BL track to perform the same function in the new layout. As with many such questions the answers lay in the bookwirings and strip prints, becoming evident when the circuitry is closely examined.
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