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Post by spsmiler on Oct 25, 2021 9:55:30 GMT
Someone asked me this:
I guess that the lines which still have fixed size blocks have the signals whilst the others (which use moving blocks) do not because there are no fixed stopping points. (apart from junctions and stations)
But am I correct here?
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Colin
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Post by Colin on Oct 25, 2021 12:46:12 GMT
In simple terms yes, there's perhaps some truth in the fixed block versus moving block comparison.
The actual answer though is simply that ATO (Automatic Train Operation) lines which have some colour light signals are an older technology whereas the more recently converted ATO lines (ie, Jubilee, Northern and the current Sub Surface Railway's ongoing conversion) are a much newer technology employing in cab signalling thus negating the need for lineside signalling outside of the train cab.
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Tom
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Post by Tom on Oct 25, 2021 19:26:07 GMT
One could argue there are signals in the Thales product - the RM Hold boards and Route Secure signs are both authorities to proceed and passing one without authority is, as I understand it, treated the same as a SPAD.
It's a similar situation to the white aspect on the Central line; if you are in either ATO or Coded Manual you can pass it. The difference between Central Line ATP and Seltrac is that the movement authority is being constantly updated with Seltrac, whereas it's more fixed with the Central (and to a lesser extent, the Victoria) and there is much less provision for degraded working on the T/CBTC lines.
That said in the Zone 1 section of the Central line there is little other than starters or signals protecting points; the rest is all trackside signage.
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Post by North End on Oct 25, 2021 21:40:05 GMT
One could argue there are signals in the Thales product - the RM Hold boards and Route Secure signs are both authorities to proceed and passing one without authority is, as I understand it, treated the same as a SPAD. It's a similar situation to the white aspect on the Central line; if you are in either ATO or Coded Manual you can pass it. The difference between Central Line ATP and Seltrac is that the movement authority is being constantly updated with Seltrac, whereas it's more fixed with the Central (and to a lesser extent, the Victoria) and there is much less provision for degraded working on the T/CBTC lines. That said in the Zone 1 section of the Central line there is little other than starters or signals protecting points; the rest is all trackside signage. Passing an RM Hold board without authority is indeed a SPAD, though by definition only in RM. The main likelihood for it happening is either getting mixed up when carrying out a move in RM, or putting the train into RM by mistake. Both have happened, and it is potentially quite nasty as there’s nothing to stop the train so it could carry on for some distance if no one notices. An RS board isn’t an authority, it’s merely an indication to give added confidence. This is no different to how things were under signals. The authority to move will come from the signaller - he should ask the driver “are you standing at XXXboard, and can see a route secure visual illuminated with a number 2?”, and if the response is yes then authority to move would then be given. The driver would never move just on authority of an illuminated RS, in so doing this would also involve passing an RM Hold board, against which the SPAD would then be recorded. The original purpose of RS was to give the driver confidence that points didn’t need to be manually secured, with TBTC it is also acceptable for verbal authority subject to confirmation from the VCC Operator in the room - if for whatever reason an RS can’t be obtained, or if the train isn’t standing at one (or perhaps if there isn’t an RS for the move desired - this has happened a few times when they’ve wanted to bring a defective train out of Kennington siding straight onto the southbound in order to run it down to Morden without having to faff around). |
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Post by North End on Oct 25, 2021 21:43:38 GMT
In simple terms yes, there's perhaps some truth in the fixed block versus moving block comparison. The actual answer though is simply that ATO (Automatic Train Operation) lines which have some colour light signals are an older technology whereas the more recently converted ATO lines (ie, Jubilee, Northern and the current Sub Surface Railway's ongoing conversion) are a much newer technology employing in cab signalling thus negating the need for lineside signalling outside of the train cab. It’s a matter for debate whether Seltrac TCTC/CBTC is a newer technology than the Victoria Line’s DTG-R, bearing in mind London has been running Seltrac since the early 90s on the DLR. The presence of signals is more to do with the system architecture, which is simply different between the systems. I seem to recall there was once some inference that the Central Line had signals as part of a very aspirational idea to allow non-ATP-fitted engineers trains to run, presumably during a possession or whatever. This did actually happen for the overnight Central Centenerian rail tour using the 1960 stock. There doesn’t seem any other obvious reason for why the longer sections on the Central Line do have occasional signals - the Victoria Line Upgrade generally didn’t bother with this. |
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Tom
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Post by Tom on Oct 26, 2021 7:56:57 GMT
An RS board isn’t an authority, it’s merely an indication to give added confidence. Good point - what I should have said was an RM Hold board has the same authority as a red aspect in the old days. It’s a matter for debate whether Seltrac TCTC/CBTC is a newer technology than the Victoria Line’s DTG-R, bearing in mind London has been running Seltrac since the early 90s on the DLR. Oh that's easy - it's not. I've been looking through some old issues of Underground News recently and Seltrac was being considered for the Northern line as far back as 1990! DTG-R is the more modern product, though elements of it are based on the failed attempt at Westinghouse Moving Block on the Jubilee Line Extension. |
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Colin
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Post by Colin on Oct 26, 2021 8:56:27 GMT
To clarify, when I said "newer technology" I was thinking more about the in cab signalling element than the whole ATO set up as the original question was specifically asking about colour light lineside signals.
I'm well aware that the base of the Seltrac product dates back to the 1970's
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Post by Deleted on Oct 26, 2021 15:06:20 GMT
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Post by principlesdesigner on Oct 26, 2021 21:06:10 GMT
There was (is?) a rule that there had to be a signal every 1.1km
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Tom
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Post by Tom on Oct 26, 2021 21:19:13 GMT
Was that a Central Line specific thing? I don't recall it in the standards. (And it's been several years since I've had access to a copy of the CLP Signalling Contract.)
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Post by spsmiler on Oct 27, 2021 12:15:28 GMT
An RS board isn’t an authority, it’s merely an indication to give added confidence. Good point - what I should have said was an RM Hold board has the same authority as a red aspect in the old days. I assume that these RM Hold boards are white with a red slash (top right to lower left)? Why do I ask? I am currently editing my next YouTube video and it will include a train stopping at one of these boards. The train had just left Roding Valley station and joined the main line from Epping,* and in the distance the back of the train in front can be seen passing a red signal immediately prior to arriving at Woodford station. *Although just outside Roding Valley station I think this is called Woodford Junction. |
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Post by Dstock7080 on Oct 27, 2021 14:25:08 GMT
I assume that these RM Hold boards are white with a red slash (top right to lower left)? Why do I ask? I am currently editing my next YouTube video and it will include a train stopping at one of these boards. The train had just left Roding Valley station and joined the main line from Epping,* and in the distance the back of the train in front can be seen passing a red signal immediately prior to arriving at Woodford station. *Although just outside Roding Valley station I think this is called Woodford Junction. what you describe on the Central Line are ATP marker boards. CBTC SSR (and Northern/Jubilee TBTC are similar) RM Hold board:  |
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Post by principlesdesigner on Oct 27, 2021 16:24:17 GMT
Was that a Central Line specific thing? I don't recall it in the standards. (And it's been several years since I've had access to a copy of the CLP Signalling Contract.) I seem to recall that it was also a requirement on the VLU |
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Post by spsmiler on Oct 29, 2021 10:53:42 GMT
what you describe on the Central Line are ATP marker boards. Thanks, I've been reading Clive's Underground guide on this signalling system and he calls them block section markers. It is indeed at one of these that I saw a train come to a halt. www.davros.org/rail/signalling/articles/central.html
As an aside, he also says that for westbound trains ATP was introduced between West Acton and Ealing Broadway on 2002-03-04 and withdrawn 2002-03-11. I wonder why? I would be surprised if it has not now been reinstated (he does not say this has happened).
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North End
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Post by North End on Oct 29, 2021 15:58:57 GMT
what you describe on the Central Line are ATP marker boards. Thanks, I've been reading Clive's Underground guide on this signalling system and he calls them block section markers. It is indeed at one of these that I saw a train come to a halt. www.davros.org/rail/signalling/articles/central.html
As an aside, he also says that for westbound trains ATP was introduced between West Acton and Ealing Broadway on 2002-03-04 and withdrawn 2002-03-11. I wonder why? I would be surprised if it has not now been reinstated (he does not say this has happened).
Whilst block section marker is a decent description, “block marker board” (BMB) is the correct term. |
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Post by t697 on Oct 29, 2021 16:27:33 GMT
I assume that these RM Hold boards are white with a red slash (top right to lower left)? Why do I ask? I am currently editing my next YouTube video and it will include a train stopping at one of these boards. The train had just left Roding Valley station and joined the main line from Epping,* and in the distance the back of the train in front can be seen passing a red signal immediately prior to arriving at Woodford station. *Although just outside Roding Valley station I think this is called Woodford Junction. what you describe on the Central Line are ATP marker boards. CBTC SSR (and Northern/Jubilee TBTC are similar) RM Hold board: Seems quaint to describe an RM Hold board as 'Co-Acting' considering they are completely inert unlike a traditional signal which can change aspect, but what do I know...! |
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Post by jimbo on Oct 29, 2021 18:49:37 GMT
They are signs acting as signal replacements? Two provided for sighting problems at this site? Need to distinguish between the two for reporting purposes.
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Tom
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Post by Tom on Oct 29, 2021 19:20:11 GMT
As an aside, he also says that for westbound trains ATP was introduced between West Acton and Ealing Broadway on 2002-03-04 and withdrawn 2002-03-11. I wonder why? I would be surprised if it has not now been reinstated (he does not say this has happened). It wasn't ATP, it was ATO. It was found that the stopping tolerances in Ealing Broadway platforms were such that the last set of doors could be off the platform if the train stopped short of the stopping position but still within tolerance. There was a small (c.2m) platform extension to address the risk and ATO was subsequently reinstated once this was built. As an aside (and probably for another thread if anyone wasnts to raise it); there are a couple of errors in the article you mention. |
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Tom
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Post by Tom on Oct 29, 2021 19:21:52 GMT
They are signs acting as signal replacements? Two provided for sighting problems at this site? Need to distinguish between the two for reporting purposes. Two for sighting purposes, replacing the previous signal and co-acting signal at this location. I'm not sure how necessary the second set of RM Hold boards was, bearing in mind the Co-acting signal was provided for the differences in sighting between C and S stock, but none the less that's what was provided. |
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Post by jimbo on Oct 29, 2021 21:15:02 GMT
Perhaps easier to put up a co-acting sign than to negotiate that it is no longer necessary?
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Post by greggygreggygreg on Oct 29, 2021 21:39:29 GMT
Perhaps easier to put up a co-acting sign than to negotiate that it is no longer necessary? Or, if the co-acting is removed, and there's an incident, then the person who authorised its removal is at fault |
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Tom
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Post by Tom on Oct 30, 2021 8:23:40 GMT
Perhaps easier to put up a co-acting sign than to negotiate that it is no longer necessary? I was thinking a bit more about this. The berth at Hammersmith is particularly tight, and with the cab pillars ion S stock being the way they are, it might be that an under/overstop, even if within tolerance, would place the sign out of view. Knowing how much all LU projects are expected to be cost-conscious, I cannot believe it was simply because someone didn't negotiate (or didn't negotiate well enough) - there must be a reason for it. Unfortunately, the Signal Sighting Project Manager at the time is no longer working for TfL, so I can't ask them! |
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Post by t697 on Oct 30, 2021 8:58:25 GMT
I wasn't doubting that the two signs were necessary under sighting rules, probably due to cab pillars and stopping tolerances as described. I was just noting that 'co-acting' seems an odd description of a completely inert object!
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Post by alpinejohn on Oct 30, 2021 11:33:58 GMT
If the image posted above by Dstock7080 is fairly recent it is rather worrying. Black plastic bin liners do not last forever and presumably were installed at some stage during the switchover from Conventional light signalling. As a short term (potentially reversible) fix this makes sense but this late in the day I rather doubt the covered up signals will ever be considered for reinstatement.
Hopefully the signal lights have all been powered down by now or there is a risk that once those plastic bags degrade after many years in sunlight then it must only be a matter of time before drivers may encounter an unexpected signal aspect light despite being told by the onboard kit that he is cleared to proceed.
Is there a programe to remove these potentially distracting legacy signalling?
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Post by Dstock7080 on Oct 30, 2021 11:50:55 GMT
Hopefully the signal lights have all been powered down by now . . . . Is there a programe to remove these potentially distracting legacy signalling? Legacy signalling is powered down and there is no programme to remove them. |
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Post by bpk on Oct 30, 2021 12:34:32 GMT
As an aside, he also says that for westbound trains ATP was introduced between West Acton and Ealing Broadway on 2002-03-04 and withdrawn 2002-03-11. I wonder why? I would be surprised if it has not now been reinstated (he does not say this has happened). It wasn't ATP, it was ATO. It was found that the stopping tolerances in Ealing Broadway platforms were such that the last set of doors could be off the platform if the train stopped short of the stopping position but still within tolerance. There was a small (c.2m) platform extension to address the risk and ATO was subsequently reinstated once this was built. As an aside (and probably for another thread if anyone wasnts to raise it); there are a couple of errors in the article you mention. This goes some way to explaining why entering Ealing Broadway in Coded Manual can be slightly tricky. ATP gives you 10 seconds or so to traverse the last signalling block. If you take more than a couple of seconds to berth your train than the ATP allows (ie you're ever so slightly slower) you get code tripped just as you reach the stopping mark, bringing you to a rather sudden stop than desired! |
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Post by Deleted on Oct 30, 2021 13:44:50 GMT
Hopefully the signal lights have all been powered down by now . . . . Is there a programe to remove these potentially distracting legacy signalling? Legacy signalling is powered down and there is no programme to remove them. Not all of it is powered down but certainly the track circuits and the aspects are |
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Tom
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Post by Tom on Oct 30, 2021 15:14:35 GMT
Black plastic bin liners do not last forever and presumably were installed at some stage during the switchover from Conventional light signalling. As a short term (potentially reversible) fix this makes sense but this late in the day I rather doubt the covered up signals will ever be considered for reinstatement. Hopefully the signal lights have all been powered down by now or there is a risk that once those plastic bags degrade after many years in sunlight then it must only be a matter of time before drivers may encounter an unexpected signal aspect light despite being told by the onboard kit that he is cleared to proceed. Is there a programe to remove these potentially distracting legacy signalling? The fuses to the legacy signal aspects are all removed shortly after commissioning, in line with LU's standards. The 4LM project team is only too aware that the bin liners degrade after a period of time and there is a project team within the 4LM portfolio dedicated to redundant assets. The problem is the availability of staff to undertake the removal works, as the same members of staff are also engaged in Earthing and Bonding alterations following the removal of the legacy track circuits, and the removal of redundant capactitors in order to comply with an Environmental Agency directive placed upon TfL. As I'm sure you'll understand, their effords need to be focussed on meeting the organisation's Health and Safety obligations before the removal of anything else. |
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Tom
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Post by Tom on Oct 30, 2021 15:18:50 GMT
This goes some way to explaining why entering Ealing Broadway in Coded Manual can be slightly tricky. ATP gives you 10 seconds or so to traverse the last signalling block. If you take more than a couple of seconds to berth your train than the ATP allows (ie you're ever so slightly slower) you get code tripped just as you reach the stopping mark, bringing you to a rather sudden stop than desired! One for another thread, I think, but you should have a minute to correct your stopping position before the code is taken away from you. |
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Post by North End on Oct 30, 2021 15:49:08 GMT
This goes some way to explaining why entering Ealing Broadway in Coded Manual can be slightly tricky. ATP gives you 10 seconds or so to traverse the last signalling block. If you take more than a couple of seconds to berth your train than the ATP allows (ie you're ever so slightly slower) you get code tripped just as you reach the stopping mark, bringing you to a rather sudden stop than desired! One for another thread, I think, but you should have a minute to correct your stopping position before the code is taken away from you. I can attest to it being as previously described - I’ve been “got” by it, probably thanks to having spent time becoming used to the excessively gentle open-air brake rates on certain other ATO lines. Too gentle down on the mark and it loses code. Unlike those certain other ATO lines, at least on the Central this can be sorted pretty readily. This is with the caveat that this is for platform 6. No idea if same applies for platform 5. |
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