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Signal Time Out 30/11/2023 at 09:38 #154534 | |
Giantray
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I know today's standard is four minutes for when a signal is replaced holding the route, to when the route releases. A degrogation order had to be made to lower this when London Bridge ASC was resignalled/controlled at TBROC. A four minute time-out would have crucified the service in the London Bridge area, we got it reduced to two minutes on running lines and 30 seconds at termini starting signals. Doncaster like Kings Cross PSB also had that annoying signal would time-out even with no train any where near it. Again at London Bridge so long as there was no train approaching signals in rear that would receive a change of aspect, the signal when replaced would release the route immediately. I can understand the four minute time-out in areas where trains run at 125 mph. What I do not understand is why a signal will time-out with no train anywhere? Does anyone know the history behind this? Professionalism mean nothing around a bunch of Amatuer wannabees! Log in to reply |
Signal Time Out 30/11/2023 at 10:07 #154535 | |
Javelin395
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First of all, I'm not a professional railwayman. However, I do seem to recall similar discussions elsewhere on this forum. From memory, the reason given for the annoying timeout when a train was nowhere near the signal being pulled was the extra cost of additional circuitry involved. Presumably the extra coding required adds to the cost of IECC installations. I would also postulate that a blanket four minutes timeout obviates the need for expensive, case-by-case safety assessments. Log in to reply |
Signal Time Out 30/11/2023 at 10:08 #154536 | |
Steamer
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'Looking back' to see if a train is approaching requires more design work and, in the case of relay interlocking, additional circuits. Presumably at London Bridge the cost could be justified, but not elsewhere.
"Don't stress/ relax/ let life roll off your backs./ Except for death and paying taxes/ everything in life.../ is only for now." (Avenue Q) Log in to reply The following user said thank you: Giantray |
Signal Time Out 30/11/2023 at 10:14 #154537 | |
Giantray
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Steamer in post 154536 said:'Looking back' to see if a train is approaching requires more design work and, in the case of relay interlocking, additional circuits. Presumably at London Bridge the cost could be justified, but not elsewhere.Yes money always has a hold on what is and is not achieveable. I don't know if the time-out or route release was changed when Kings Cross PSB went to York ROC. I'll have to find out. Professionalism mean nothing around a bunch of Amatuer wannabees! Log in to reply |
Signal Time Out 30/11/2023 at 10:40 #154538 | |
headshot119
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There's two types of approach locking, comprehensive which looks back to see if a train is approaching, and none comprehensive where the signal will time out regardless. Cost and complexity in relay interlockings is the usual reason for none comprehensive. The part of Kings Cross that was resignalled quite possibly now has "Comprehensive" approach locking. I believe the parts which are a straight recontrol don't have TORR on the new workstations, so I'd be surprised if they've fiddle with the approach locking. "Passengers for New Lane, should be seated in the rear coach of the train " - Opinions are my own and not those of my employer Log in to reply The following user said thank you: Giantray |
Signal Time Out 30/11/2023 at 13:02 #154541 | |
clive
![]() 2766 posts |
Giantray in post 154534 said:"Simple" approach control, where the signal just times out when the route is pulled, only requires a couple of relays and all the logic is in one place. "Comprehensive" approach control, where it only times out if a train is approaching, requires much more logic because it has to check three or four sections back, which could require lots of circuitry to deal with pointwork (is the approaching train actually heading for this signal? is track circuit DK actually occupied because a train is crossing over a diamond and again, not heading for this signal? how many different signals could change aspect if this one goes from green to red [1]). A lot more relays and a lot more cost. I've also got a vague idea that comprehensive approach locking was a relatively late addition to UK signalling, with London Bridge being the first PSB to have it. But I could be wrong there. [1] The Down Fast at Peterborough through the station has, if I recall correctly, five signals in a row that all have to have a route set before any of them will come off on a clear line. So the look-back can be a lot further than you think. Log in to reply The following user said thank you: Giantray |
Signal Time Out 30/11/2023 at 13:06 #154542 | |
clive
![]() 2766 posts |
headshot119 in post 154538 said:That's what I would expect. King's Cross interlocking (which I think covered Belle Isle), in the PSB building, was scrapped and replaced by a computer-based interlocking when the layout was redone a few years ago. Comprehensive approach control is pretty simple in CBIs - a bit more design and a bit more testing, of course, but the testing can be done before installation and the design patterns are well-known; much of it is probably in their equivalent of the core code. It's probably got TORR for the same reason. The rest of KX's territory was just recontrolled to York but the interlockings haven't changed. So no approach locking and no TORR. IIRC, Cambridge doesn't have comprehensive approach locking either for the same reason, at least south of Ely (Ely onwards is all CBIs). Log in to reply |
Signal Time Out 30/11/2023 at 22:35 #154555 | |
flabberdacks
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When you say 'no TORR' for the recontrolled workstations, is it that the workstation software itself sends a route cancel command automatically once certain conditions are met, as opposed to it happening in the interlocking? NSW relay interlockings that were re-controlled to computer workstations do it that way Log in to reply |
Signal Time Out 30/11/2023 at 23:44 #154556 | |
GeoffM
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clive in post 154541 said:"Simple" approach control, where the signal just times out when the route is pulled, only requires a couple of relays and all the logic is in one place."Locking", not control! SimSig Boss Log in to reply |
Signal Time Out 30/11/2023 at 23:45 #154557 | |
GeoffM
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flabberdacks in post 154555 said:When you say 'no TORR' for the recontrolled workstations, is it that the workstation software itself sends a route cancel command automatically once certain conditions are met, as opposed to it happening in the interlocking?It's certainly been done in the UK. IIRC the safety case was "only" safety-related, not safety-critical, so it was a little easier to implement. Still requires a sequence of track occupations and clearances. SimSig Boss Log in to reply |
Signal Time Out 01/12/2023 at 12:44 #154559 | |
kbarber
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clive in post 154541 said:Giantray in post 154534 said:Interesting that the standard has become 4 minutes; used to be 2 minutes except on single lines where 4 minutes applied."Simple" approach control, where the signal just times out when the route is pulled, only requires a couple of relays and all the logic is in one place. Some of the signals on Old Oak Panel had comprehensive approach locking. Whether that was from new (1967) or retro-fitted (I saw it in summer 1979) I wouldn't like to say. Log in to reply |
Signal Time Out 01/12/2023 at 23:26 #154571 | |
clive
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GeoffM in post 154556 said:clive in post 154541 said:Oops. Sorry."Simple" approach control, where the signal just times out when the route is pulled, only requires a couple of relays and all the logic is in one place."Locking", not control! Log in to reply |
Signal Time Out 06/12/2023 at 16:08 #154616 | |
Izzy
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A very quick summary of approach locking from a retired Box T.O. / Designer..... (as always, there may be exceptions and regional differences, but as a rule of thumb.....) What i will call "Simple" approach locking was historically the norm. ie. Once the signal clears (shows a proceed aspect), cancelling a route without passage of a train will result in timing out. The correct term is "Approach Locked when Cleared" - but simple is easier to type, so i'll use that. The rules used to be (i haven't looked at them for quite a while) 120 seconds for a main route, 30 seconds for a shunt route. The 120 can be extended to 240 seconds in certain circumstances like very high linespeed, or very steep approach gradient - or indeed lowered to 30sec in very special situations like platform starters as mentioned above. This general rule of thumb means that a main signal showing a call-on or shunt aspect will time out for the full 120sec. NOT the 30 second shunt route time (as i have seen in some simulations, but not bothered posting about) - This is because the approaching train is approaching a main aspect at red, and thus the full main route timer is used. And if you want really restrictive - in the old days when Margate had it's lever frame, there was no approach lock release cicuitry or timers - if the signalman pulled off in error, then he had to get the S&T out (at least, officially). I am sure this wasn't unique in older interlockings - and every signalman i ever knew who signed Margate was very aware of this trap!!! Comprehensive approach locking was rare outside the Southern region until the advent of electronic interlockings. However, it would be provided as requested by the operating department (at extra cost), or almost always where a signal has an associated auto button. The look back circuitry in relay interlockings was extensive and could get quite complicated in places, and this is why comprehensive locking wasn't provided as standard (outside the southern) - but if an auto button is provided it is assumed that it is very likely that route will be cancelled by the signaller for a specific reason, for example to change routing at a rarely used crossover, so to enforce a time out with no train approaching was unduly restrictive - and worth the extra cost. Comprehensive approach locking is still by no means a standard provision - Trowell interlocking in the East Mids. control centre is an example of a relatively recent interlocking with 4 minute time outs and simple approach locking. I believe this decision was made as the interlocking is quite full, and they were running out of processor time, so instead of adding another interlocking, they cut the comprhensive locking out. A relatvely low traffic route and cost considerations above what is often now considered standard. As i have said many times on this forum - there are very few hard and fast rules. As TORR crept in to the post - TORR was designed originally for the (original) London Bridge scheme, so is very rare on relay interlockings outside the Southern and even then only a few were fully provided with it. TORR is much easier to provide on CBI's (computer based interlockings), and i believe it is now a standard provision. Interestingly - the TORR relay cicuitry isn't that complicated either, it just wasn't done until somebody thought it might be handy at London Bridge. None of the early Geographical interlockings had TORR as their design pre-dated the idea, so it had to be free-wired afterwards - the later GEC Geographicals (not AGS or SGE), and Westpac Mk4 had the pre-wired necesities for TORR (whether it was used or not). And of course a bespoke free wired interlocking would be designed with it. The circuit uses already provided relays - just a little bit of extra wiring that is already needed for the interlocking to work - as opposed to comprehensive approach locking which specifically needs extra functions and thus relays to be added. So the general rule outside of the Southern is unless a signal has an auto button, it won't have comprehensive approach locking. Which brings me to the Donny station sim. I haven't visited or worked there, so i can't say for sure - but i was very surprised there is no comprhensive approach locking on the auto buttoned signals - if this is just something that got overlooked in the sim. then so be it - but i would be very surprised if that was the case in real life - as having to time out often negates or at least severely hinders the reason for providing an auto button in the first place. One other thing i have seen in SimSigland regarding auto working buttons - specifically on the Derby sim.....On the Wichnor interlocking, there 2 signals on the up main 79 and 81 that time out for 3/4 minutes at the entrance to Central Rivers. This is an error - the signals were (and still are) provided with comprehensive app locking. But, when the Simsig crowd visited, there was an interlocking fault which caused 79 signal to work simple app locking. The fault had been there for some years, and no-one had bothered reporting it, to the point that most signallers believed it was working correctly, and just lived with it. I fixed it when i worked there and became aware of it. So, if anyone wants to fix the Derby sim, feel free - or we can just live with the fault - just as they did a Derby for quite a few years. 81 never had a fault and always worked comprehensive app locking with a 3 minute timer. 79 was the signal with the fault, it should work with comprehensive app locking with a 240 sec. timer. This 4 minutes timer means you have to be pretty quick if a voyager for central rivers comes from Tamworth as you only have 1 signal section before you cause a change of aspect because of the double red provision at Wichnor. I hope this of some interest to someone out there. Any questions, feel free to ask me - but please don't expect an immediate reply, although i'll try to be timely. PS. Clive - comprehensive app locking wasn't first on London Bridge - a lot of the earlier southern power schemes had it in selected places/signals - Dartford and Feltham had it. Last edited: 06/12/2023 at 16:48 by Izzy Reason: None given Log in to reply The following users said thank you: postal, Dionysusnu, Splodge, mldaureol, broodje, Javelin395, flabberdacks, JWNoctis |
Signal Time Out 06/12/2023 at 17:14 #154617 | |
GeoffM
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Izzy in post 154616 said:So the general rule outside of the Southern is unless a signal has an auto button, it won't have comprehensive approach locking. Which brings me to the Donny station sim. I haven't visited or worked there, so i can't say for sure - but i was very surprised there is no comprhensive approach locking on the auto buttoned signals - if this is just something that got overlooked in the sim. then so be it - but i would be very surprised if that was the case in real life - as having to time out often negates or at least severely hinders the reason for providing an auto button in the first place.Thanks for the comprehensive (sorry) history on approach locking. I do have the control tables for Doncaster and can confirm the entries say "When cleared" under the approach locking columns. Also no TORR. My understanding of a call-on on a signal capable of showing main aspects was that in relay days a single timer would be used so the longest timeout required would apply to all types of routes from that signal. In CBI days this is different for the different types of route (30s for call-on/shunt; 120 or more for main aspect; 60s for a bay platform). SimSig Boss Log in to reply |
Signal Time Out 06/12/2023 at 18:04 #154618 | |
Izzy
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Thanks for that Geoff. I must say i am surprised they bothered to put auto buttons on approach locked when cleared signals - but i didn't say it couldn't happen, LOL. As for the shunt timeout associated with main aspect.....i can't say for sure,as i am a bit out of date - but i always understood that the longer timeout was used because of the poosible approach speed from the signal in rear. A 30 second timeout for a train that could have passed a single yellow at 50 - 60 mph seems a little short to prove the train at a stand before route release (which is the timer's raison d'etre), so the type of interlocking is irrelevant. But, i could be wrong ![]() Last edited: 06/12/2023 at 18:09 by Izzy Reason: None given Log in to reply |
Signal Time Out 06/12/2023 at 19:14 #154619 | |
GeoffM
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Izzy in post 154618 said:Thanks for that Geoff. I must say i am surprised they bothered to put auto buttons on approach locked when cleared signals - but i didn't say it couldn't happen, LOL.I must admit I'd never heard of that before. I don't actually recall seeing any control tables where there was a correlation between auto buttons and comprehensive approach locking - usually it's either nearly all signals have it, or none. But again, I'm not saying it didn't happen, it's just that I haven't seen it! Izzy in post 154618 said: As for the shunt timeout associated with main aspect.....i can't say for sure,as i am a bit out of date - but i always understood that the longer timeout was used because of the poosible approach speed from the signal in rear. A 30 second timeout for a train that could have passed a single yellow at 50 - 60 mph seems a little short to prove the train at a stand before route release (which is the timer's raison d'etre), so the type of interlocking is irrelevant. But, i could be wrong :)Different timeout values seems to have been normal on CBIs since at least the late 1980s. Bethnal Green, for example, has 60s for warner routes and 120s for main routes which I think dates from 1989 if memory serves. Recent re-signalling seem to have anywhere from 2 to 4 minutes for main routes, for example 3 minutes is reportedly common on the forthcoming Colwich re-interlocking. SimSig Boss Log in to reply |
Signal Time Out 06/12/2023 at 19:28 #154620 | |
Izzy
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"Different timeout values seems to have been normal on CBIs since at least the late 1980s. Bethnal Green, for example, has 60s for warner routes and 120s for main routes which I think dates from 1989 if memory serves. Recent re-signalling seem to have anywhere from 2 to 4 minutes for main routes, for example 3 minutes is reportedly common on the forthcoming Colwich re-interlocking." Yes, but my point is that a sub signal associated with a main aspect should have the main aspect time off - as it is a main signal. That is why it is called a subsidiary, and not a shunt signal head. For similar reasons we used to get loads of trains appraoching cat's eyes getting TPWS overspeed applications - the signal is a main signal, even if it dispalys a "shunt" aspect...the driver was expecting to be able to brake down to shunting speed by the time he reached the signal, but the design was treating the main signal at danger - even if the cat's eyes were lit (it technically is at danger - a sub aspect is one of the authorities listed in the rules to pass a signal at danger). So, although the trainstop grids were suppressed, the overspeeds were still active. I'd be interested to know of somewhere where the sub route of a main signal only times for 30 seconds - it goes against the principle of making sure an approaching train is at a stand before releasing the onward route. The timeout value is designed with approach speed in mind, not only what class of route is set. Or at least that's how i was taught to do it. Last edited: 06/12/2023 at 20:03 by Izzy Reason: None given Log in to reply |
Signal Time Out 06/12/2023 at 23:45 #154628 | |
clive
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GeoffM in post 154617 said:That's my understanding as well, from the Big Green Book. To have multiple times would require not just more than one timing relay but several other relays to select which timing relay to use. There's almost certainly not enough benefit to do that. GeoffM in post 154617 said: Surely it should be the route class for the approaching train, not for the route set for the signal, that matters. I can see Izzy's point that if a train is approaching a red at main-line speeds and braking, you want the full 120 seconds even if it's a calling-on route that's been pulled. But equally, if the train is coming out of a siding on two whites, 30 seconds should be enough even if it's a main route that's been pulled. Log in to reply |
Signal Time Out 07/12/2023 at 00:05 #154629 | |
Izzy
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Quote:Yes, but the route class in rear is lost as the train enters that route, the entry route "class relay" (MER, SER, MER(C), (M,S,W or C) NLR, amnogst others depending on interlocking type (not exhaustive) ) begins to release that route behind the train as soon as it replaces the entry signal. So, the signal that you pull the button on in many cases has no way of knowing what class route was set up to it. Hence we use the longest, worst case, timer length. In theory, it is possible to register this info in a CBI (or even if a turnback move is being made and therefore has an approach speed of 0) - but this is all extra work for little benefit, you shouldn't be pulling buttons in front of trains anyway (in most cases), so we make do with the longer time penalty. Quote: GeoffM in post 154617 said:Yep, this is exactly how it is done. My doubt is about whether a main signal with subsidiary cat's eyes will have a 30s timeout in any shunt or call-on route set from it - it should be the full main signal timeout value, at least 60s upto a maximum of 4 minutes. Last edited: 07/12/2023 at 00:30 by Izzy Reason: None given Log in to reply |
Signal Time Out 07/12/2023 at 00:39 #154630 | |
Izzy
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To sum up - Main signal (with or without subsidiary head) = 60s - 240s timeout (normally 120s, but up to 240s depending on maximmum permissible approach speed). Shunt signal = 30s timeout A main signal with warning class route can have 2 timer values - the main 60-240s value. Or a warning route reduced timout - this is justified by the fact we can guarantee any approaching train has been slowed down before the delayed yellow aspect is displayed, so we don't need the full 120, 180 or 240 second timeout for maximum permissible speed. This could the case in relay interlockings as well if it were specified as part of the design. Why provide a short overlap with all the extra circuitry involved, but not take advantage of the shorter timeout allowed by it? After all, the extra flexibility has already been justified enough to provide a waner route in the first place. This main signal will never have a 30s timer, as it will never be used - because a main signal at red (with ir without cat's eyes) has an absolute minimum timeout of 60s regardless of approach speed or type of route set up to it. This is a bit beyond what giantray originally asked, but i think my first post covered that. I hope i have cleared up the misunderstandng that seems to have crept in to the latter bits. Last edited: 07/12/2023 at 01:02 by Izzy Reason: speelig mistrake Log in to reply |
Signal Time Out 07/12/2023 at 01:18 #154631 | |
TUT
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clive in post 154628 said:Surely it should be the route class for the approaching train, not for the route set for the signal, that matters. I can see Izzy's point that if a train is approaching a red at main-line speeds and braking, you want the full 120 seconds even if it's a calling-on route that's been pulled. But equally, if the train is coming out of a siding on two whites, 30 seconds should be enough even if it's a main route that's been pulled.I don't really follow this logic at all to be honest. The train should have been timed at or nearly at a stand for the calling-on to clear anyway, so if the cat's eyes have come off the system has already satisfied itself that the train isn't doing 50-60 mph hasn't it? And if the subsidiary route hasn't even cleared yet there shouldn't be any issue with cancelling the route that never came off should there. But even if the white lights came off without any approach control whatsoever I still don't see the reason why one would positively want the full timeout to be applied. I can see why one might not go to the trouble of applying a different timeout if it adds to the complexity, but I don't see why one would positively choose that as the standard because a driver will pass a single yellow and then see the big bright red clearly before the little white cat's eyes enter the picture and then the driver knows what they mean doesn't he? If it's safe for them to come off at all, if you can trust a driver to continue slowing for them at all, well then you don't need a full 120 or 240 second timeout if you take them back from him do you? He hasn't seen a main aspect come off, he hasn't stopped reducing his speed so as to 'proceed at caution towards the next train, signal or buffer stop, and be prepared to stop short of any obstruction', he hasn't started taking power because he's seen the next signal clear to a main aspect and is now getting ready to continue on at speed. If you think he might then you shouldn't be allowing the calling-on to come off in the first place, should you? The reason for the long timeouts on main signals is because you have cleared the main signal, you have given a train stopped at that signal permission to start away under a main signal, line clear to the next signal (generally + overlap), you have given a train on approach to the signal permission to keep it rolling on to the next signal, or shown the driver a sequence that tells them they can take or maintain power. Therefore if you take it back you need to allow plenty of time to make sure the driver has seen the change, responded to it and stopped or that the TPWS has had time to stop the train, or if not then you need to wait for the results of your actions to pan out, the SPAD to occur and you can't go changing junctions etc. until you can be reasonably sure there's no danger in doing so. If all you've given the driver is authority to 'to proceed at caution towards the next train, signal or buffer stop, and be prepared to stop short of any obstruction' and you should only have given them such authority when they're at or nearly at a stand anyway, I really don't see why you need 240 or even 120 seconds as a timeout. Last edited: 07/12/2023 at 01:19 by TUT Reason: None given Log in to reply The following user said thank you: GeoffM |
Signal Time Out 07/12/2023 at 01:38 #154632 | |
TUT
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I do of course appreciate that you wouldn't want to lose or override the normal timing out of the overlap (which should be getting pretty close to having timed out, if it hasn't already, when the cat's eyes come off anyway). But if we take for example Aylesbury on the Marylebone sim. ME383 on the Down Main at Aylesbury has a calling-on aspect. No points in advance of that signal are in the overlap at all and can be moved at any time with a train approaching the signal. If the calling-on were to come off I see no reason why any of them should become locked for 240 or even 120 seconds. On the other hand if we look at ME159 at Princes Risborough the facing mains crossover in advance of that signal is in the overlap. If the calling-on comes off I fully agree that those points should not be free to move straight away the signal is cancelled, but it still doesn't need 240 seconds does it?
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Signal Time Out 07/12/2023 at 02:48 #154633 | |
clive
![]() 2766 posts |
Izzy in post 154616 said:The Big Green Book says (IIRC) that signal engineers were concerned about false releases caused by a bobbing track circuit and so nobody was willing to install it for many years. It wasn't in boxes of later vintage as London Bridge, such as Cambridge or King's Cross. Izzy in post 154616 said: Okay, thanks. I was obviously mis-remembering. Log in to reply |
Signal Time Out 07/12/2023 at 03:23 #154634 | |
GeoffM
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Izzy in post 154620 said:"Different timeout values seems to have been normal on CBIs since at least the late 1980s. Bethnal Green, for example, has 60s for warner routes and 120s for main routes which I think dates from 1989 if memory serves. Recent re-signalling seem to have anywhere from 2 to 4 minutes for main routes, for example 3 minutes is reportedly common on the forthcoming Colwich re-interlocking."I was adding on to my previous comment about different values - 30s for a call-on, 60s for a warner, 120s for a main - for the same signal head. In fact, perusing through my collection of control tables, signal BK172 at Basingstoke has a 180s timeout for the A(M) route (straight), 120s timeout for the B(M) route (diverging), 60s for the B(W) route, and 30s for both the A(C) and B(C) routes! This particular signal is on plain line for the 4 signal sections prior to it, with the B(M) route approach controlled from red, 90mph approach and straight beyond; 20mph diverging. Izzy in post 154620 said: I'd be interested to know of somewhere where the sub route of a main signal only times for 30 seconds - it goes against the principle of making sure an approaching train is at a stand before releasing the onward route. The timeout value is designed with approach speed in mind, not only what class of route is set. Or at least that's how i was taught to do it.Maybe it once did but it does not appear to be the way these days. As for where main+sub signals have different timeouts, well, to be blunt, it's everywhere where there is a CBI, which means large chunks of the country these days! SimSig Boss Log in to reply |
Signal Time Out 07/12/2023 at 03:28 #154635 | |
GeoffM
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Izzy in post 154630 said:A main signal with warning class route can have 2 timer values - the main 60-240s value. Or a warning route reduced timout - this is justified by the fact we can guarantee any approaching train has been slowed down before the delayed yellow aspect is displayed, so we don't need the full 120, 180 or 240 second timeout for maximum permissible speed.But earlier you stated that a sub route on a main aspect head should have the full timeout, same as the main head, because of the approach speed. Whether it's a warner route or a call-on/sub is the same: the driver must be expecting to stop at that red signal, and the aspect sequence up to that signal is the same for both. SimSig Boss Log in to reply The following user said thank you: TUT |