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| Setting a route over a level crossing 16/11/2024 at 14:56 #159203 | |
bugsy
1795 posts |
Am I being naughty if I set a route over a level crossing before the crossing gates are lowered?
Everything that you make will be useful - providing it's made of chocolate. Log in to reply |
| Setting a route over a level crossing 16/11/2024 at 15:28 #159204 | |
TUT
545 posts |
If you're doing your Initial Signaller Training exam, yes, they take issue with that, at least with CCTV level crossings controlled by the signaller. In reality the ARS will do it and many set-ups are designed to work that way (set the route over the crossing and then it'll auto lower).
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| Setting a route over a level crossing 16/11/2024 at 15:52 #159206 | |
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bugsy
1795 posts |
[quote=TUT;post=159204]If you're doing your Initial Signaller Training exam, yes, they take issue with that, at least with CCTV level crossings controlled by the signaller. In reality the ARS will do it and many set-ups are designed to work that way (set the route over the crossing and then it'll auto lower).[/quote) Thanks. I think that I will lower the barriers before setting the route from now onwards. Shouldn't make any difference anyhow. Everything that you make will be useful - providing it's made of chocolate. Log in to reply |
| Setting a route over a level crossing 16/11/2024 at 16:04 #159208 | |
jc92
3701 posts |
NOMINALLY you could argue it opens up the possibility of a proceed aspect over an open crossing if the route is set and somehow the crossing proving circuits fail wrong side, in much the same way that you shouldn't overset a route through a track circuit failure in case an irregularity clears the route. As TUT says though, there's loads of examples of it systematically being the case this happens anyway and I'm not aware of any specific rulebook module that prevents it. "We don't stop camborne wednesdays" Log in to reply |
| Setting a route over a level crossing 16/11/2024 at 16:19 #159209 | |
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TUT
545 posts |
Yes we were also trained not to call a route until the overlap was clear (unless specifically using a reduced overlap of course). Essentially (approach control arrangements, etc. aside) they only wanted you to try and clear a signal if all the conditions to clear it were met. So it should clear straight away. I suppose it's doing your job properly, in a way. No signaller ever wants to have to rely on the interlocking. We all make the occasional impromptu test of the interlocking from time to time, just to make sure it's still working, of course, but you try not to rely on it. On the other hand ARS will set the route when the overlap is occupied, although it will wait for the route to be clear up to the exit signal and of course use of an auto button chucks it all out of the window. I think the reasoning was basically: look, if the system does it and it goes wrong, it's the system's fault. If you do it and it goes wrong, you're the one answering the difficult questions. Last edited: 16/11/2024 at 16:20 by TUT Reason: None given Log in to reply The following user said thank you: DonRiver |
| Setting a route over a level crossing 16/11/2024 at 18:29 #159210 | |
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Stephen Fulcher
2088 posts 
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I have never been one to agree with the argument that you might cause a proceed with an overlap occupied or might cause a proceed with the barriers up etc. Interlockings are not designed to allow things that are fundamentally unsafe, and whilst nothing is impossible, that type of wrong side failure is rare. The main reason for not setting a route over a crossing before it is clear in SimSig for me is that if the crossing is blocked when lowered, you have to cancel all the routes before you can restroke the crossing. Many crossings, even CCTV, now have auto functions on their protecting signals and will lower automatically with a train approaching, the signaller only having to check the monitor and press clear. Log in to reply |
| Setting a route over a level crossing 16/11/2024 at 18:42 #159211 | |
GeoffM
6380 posts |
TUT in post 159209 said:On the other hand ARS will set the route when the overlap is occupied, although it will wait for the route to be clear up to the exit signal and of course use of an auto button chucks it all out of the window.IECC ARS and TREARS (and SimSig!) all have a form of the interlocking logic for each route/point so it shouldn't "test" the interlocking by calling something that won't set. It can't do more complicated logic though, so sometimes it'll not call a route when it could have done, or will try to call a route when it shouldn't - typically when multiple swinging overlaps or interlocking boundaries are concerned. The idea behind ARS calling a route with the overlap occupied was, I believe, to gain those precious few seconds that would otherwise be used to swing points. SimSig Boss Log in to reply |
| Setting a route over a level crossing 16/11/2024 at 21:18 #159212 | |
Steamer
3997 posts |
As a slight aside, it's worth noting that some level crossings in SimSig won't let you set a route until the crossing has been lowered and the clear button pressed. This is generally where the simulated box is a mechanical signalbox, where in reality you wouldn't be able to 'set the route', i.e. pull the signal lever, until the crossing has been closed.
"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) Last edited: 16/11/2024 at 21:19 by Steamer Reason: None given Log in to reply |
| Setting a route over a level crossing 17/11/2024 at 13:03 #159213 | |
lazzer
636 posts |
jc92 in post 159208 said:NOMINALLY you could argue it opens up the possibility of a proceed aspect over an open crossingOn this point, there are several signals "protecting" AHBCs that I drive trains over which display a green aspect with the barriers up. Athelney on the Down is a good example of this. You sight E12 signal at green with the barriers up, and they only lower as you approach the signal. The other day I was stopped short of Hele and Bradninch crossing on the Up, due to a trespasser incident. The signaller cleared the signal to green with the barriers still raised. I waited until I saw the barriers were down before I moved. Why is the signalling set up this way at certain crossings? If the barriers fail to lower when my train triggers the sequence, will the signal stay green? I ask because I'm not sure I've ever been told what exactly would happen in those circumstances. I should know, shouldn't I? :-) Last edited: 17/11/2024 at 13:03 by lazzer Reason: None given Log in to reply |
| Setting a route over a level crossing 17/11/2024 at 14:23 #159214 | |
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Jan
907 posts |
Because in order to minimise barrier closure times, AHBCs aren't interlocked with the signalling by design. (With a conventional level crossing, the crossing needs to be down before the train reaches the first cautionary aspect, which could be a mile or more away – with an AHBC it only needs to be down a few seconds before the train reaches the crossing itself.) I'm not sure how it is in the UK, for the German equivalent for example the design of the level crossing controls instead includes some additional redundancy in order to minimise the probability of a wrong-side failure. The one exception to "no interlocking between AHBC and signal" is when there's a signal between the strike-in point and the crossing. In order to prevent the barriers from unnecessarily closing if the signal is still at danger (because e.g. the block section ahead is still occupied, or no route has been set from the signal), in that case the crossing sequence will be delayed until the time that the signal could finally clear. The only problem with that is that if the signal is situated relatively close to the level crossing, the remaining distance between the signal and the crossing isn't long enough to ensure that the complete crossing sequence can always elapse before a train accelerating away from the signal would reach the crossing. Therefore, in that constellation once the signal could clear, it will actually be kept at danger for a few seconds longer until enough of the crossing sequence has operated. Two million people attempt to use Birmingham's magnificent rail network every year, with just over a million of them managing to get further than Smethwick. Log in to reply The following user said thank you: TUT |
| Setting a route over a level crossing 17/11/2024 at 14:37 #159215 | |
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TUT
545 posts |
AHBCs are not interlocked with signals. That's one of their many flaws. They were a cheap way to close signal boxes and gate boxes. If an AHBC fails to operate correctly an alarm will sound in the signal box and it will be necessary to take the crossing under local control and provide an attendant until the crossing has been fixed. Until an attendant arrives the driver of each train must be told to approach the crossing at caution and pass over it only if they are sure that it is safe to do so. However if it is known that the road-traffic signals are not working and the barriers have failed to lower then no train may pass over the crossing until an attendant has arrived. Of course the problem with that and the crossing not being interlocked with signals is that it will be necessary to replace the protecting signal to danger using the replacement switches. Sometimes however the train may be well within the protecting signal when the crossing should activate so the first train would have to be contacted by radio. What they would have done before radio I don't know. Shrug and console themselves that at least they had saved themselves the wages of a few signalmen I suppose. Log in to reply |
| Setting a route over a level crossing 17/11/2024 at 14:44 #159216 | |
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lazzer
636 posts |
The interesting point is if the crossing fails with a train approaching, the train passes the green signal before the alarm goes off (or before the signaller can revert it to danger or send an emergency broadcast on the GSM-R), and you have a train approaching a crossing at 100mph with the barriers up. That's the thing we don't like to think about ... Log in to reply |
| Setting a route over a level crossing 17/11/2024 at 15:05 #159217 | |
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TUT
545 posts |
We don't do we? The word 'monstrous' plays about the lips, what? However the good news is they can't be used if the speed of the train is more than 100 mph if that comes as any comfort, or if there are more than 2 lines over the crossing. I believe it also depends on the road, you wouldn't have an AHBC on a really major road and I believe you need decent visibility on the approach to the crossing as a road user. They are also, I believe, obsolescent: no new AHBCs will be provided, only replacements for existing ones and obviously routine maintenance on existing ones. Log in to reply |
| Setting a route over a level crossing 17/11/2024 at 21:55 #159218 | |
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clive
2799 posts |
TUT in post 159217 said:From memory, it's no more than 2 running lines but you're also allowed to have up to 2 sidings as well. TUT in post 159217 said: It's not the quality of the road. You're right that you need decent visibility for road users, but that's visibility of the warning lights, not visibility of approaching trains. Road users are expected to obey the road signals. What is required is that there is no reasonably chance of a queue of cars forming on the exit side of the crossing that could extend back over the tracks. So there has to be a clear exit route for cars; you can't have one of those chicanes you get at the entrance to some villages. You can't have an AHB right before a T-junction or a place where people might stop before turning right into a side road. There are other requirements for situating an AHB, but I think those are the key ones. Log in to reply The following user said thank you: TUT |
| Setting a route over a level crossing 18/11/2024 at 09:20 #159219 | |
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clive
2799 posts |
TUT in post 159215 said:AHBCs are not interlocked with signals.No, they aren't. But that doesn't automatically make them unsafe. The strike-in arrangements are duplicated. The crossing will start working if *either* the relevant track circuit is occupied *or* a treadle at the strike-in point is depressed. So it would require both a wrong-side failure of the track circuit *and* a broken treadle for the crossing to fail to strike in. If there's a second track circuit before the crossing, then occupation of that TC without the first one immediately starts the red lights to road traffic and the barriers descending without the 10 second delay followed by the 3 seconds of amber light. Each road approach to the crossing has two separate "wig-wags", so four lamps would have to fail for road users to get no warning that the barriers were about to descend. And even if all four fail, the barriers still descend and they have their own lights on them. I believe (I'm not certain of this) that the crossing has batteries to deal with a power cut from the mains supply. Again, I'm not sure, but I believe that if all the power to the barrier mechanism fails, the barriers will fall. Failure of the wig-wags or loss of power supply both cause an alarm at the signal box. Yes, it's possible for everything to go wrong. But the probability of this is extremely low. I can't think of any accident report where the cause was a wrong-side failure of the AHB itself. Log in to reply |
| Setting a route over a level crossing 18/11/2024 at 09:21 #159220 | |
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Late Turn
699 posts |
TUT in post 159215 said:Of course the problem with that and the crossing not being interlocked with signals is that it will be necessary to replace the protecting signal to danger using the replacement switches. Sometimes however the train may be well within the protecting signal when the crossing should activate so the first train would have to be contacted by radio. What they would have done before radio I don't know. Shrug and console themselves that at least they had saved themselves the wages of a few signalmen I suppose. I'd have thought that any failure mode that could result in a crossing failing to operate *at all* would also result in the "failed" indication not showing, because the approach of the train wouldn't have been detected. In other words, the crossing can't indicate failed if it doesn't know that it's meant to be operating! Yes, you could have lamps out in the road traffic signals or one or both barriers could fail to lower, but it's unlikely that this would immediately create a dangerous situation and there'd be even less time to stop the train by then (I have experienced the barriers failing to lower for my train, but S&T were present for a fault and I suspect – although it was never confirmed – that they'd incorrectly taken some action to disable the barriers. I managed to stop just short of the crossing in time to see an S&T bod literally hanging off one of the barriers trying to pull it down!). Log in to reply |
| Setting a route over a level crossing 18/11/2024 at 09:22 #159221 | |
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clive
2799 posts |
I'll add that I don't like AHBs, but that's because too many road drivers don't handle them properly.
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| Setting a route over a level crossing 18/11/2024 at 12:06 #159222 | |
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lazzer
636 posts |
clive in post 159221 said:I'll add that I don't like AHBs, but that's because too many road drivers don't handle them properly.That, of course, is the one thing that the railway cannot legislate for - people who drive around the barriers ... Log in to reply |
| Setting a route over a level crossing 18/11/2024 at 13:25 #159223 | |
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clive
2799 posts |
lazzer in post 159213 said:Yes, that's what you would expect with an AHB. The signals don't protect the crossing in normal operation, though the last signal before the crossing - if it isn't controlled - will have an emergency replacement button. lazzer in post 159213 said: You were lucky. The last signal could have been before the strike-in point, in which case the barriers will stay up until you pass the signal or (if it's double track) a train comes in the other direction. lazzer in post 159213 said: Yes, the signal will stay green. They're not connected unless the signal is less than 27 seconds running time from the crossing. Also note that, on double track, the barriers don't start to lower until 16 seconds after you've struck in (on single track it's 6 seconds). You should be able to see the treadles that are part of the strike-in point to work out where it is. Log in to reply |
| Setting a route over a level crossing 18/11/2024 at 13:35 #159224 | |
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clive
2799 posts |
clive in post 159219 said:Sorry, two broken treadles: there's one on each rail, I think. Log in to reply |
| Setting a route over a level crossing 18/11/2024 at 13:40 #159225 | |
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bill_gensheet
1431 posts |
clive in post 159224 said:clive in post 159219 said:Are the two not so that both need to be down to activate - as a precaution against outside interference ?Sorry, two broken treadles: there's one on each rail, I think. Kids, animals etc Log in to reply |
| Setting a route over a level crossing 18/11/2024 at 14:47 #159226 | |
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clive
2799 posts |
Let's consider a double track with a 100 mph (44.7 m/s) limit on it. Strike-in happens at a distance of 1654 metres, 37 seconds running time from the crossing. At this point any failure is purely internal to the crossing logic. After 10 seconds the amber road lights come on. We're now 1207 metres away. This is the first time an external observer can detect that there's been a failure. They stay on for another 3 seconds (134 metres) before switching to the red flashing lights. After another 5 seconds, putting us 849 metres away, the barriers start to fall. The descent time is required to be between 6 and 10 seconds, so typically I'd expect the motion to become visible two seconds later, so 760 metres (17 seconds running time) from the crossing. At 9%g (typical maximum service braking) you will reach the crossing at 57 mph some 22 seconds later. At 12%g (typical emergency braking) that becomes 32 mph and 26 seconds. That assumes no reaction time on the part of the driver. Log in to reply |
| Setting a route over a level crossing 18/11/2024 at 17:20 #159227 | |
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clive
2799 posts |
bill_gensheet in post 159225 said:clive in post 159224 said:Good question. I don't have detailed enough circuit diagrams to answer it, I'm afraid.Are the two not so that both need to be down to activate - as a precaution against outside interference ? I also tried using Google Maps to look at the treadles. The only ones I could find were strike-out treadles (i.e. front of train has passed the crossing) and those were only on one track. Log in to reply |
| Setting a route over a level crossing 19/11/2024 at 08:32 #159233 | |
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clive
2799 posts |
Late Turn in post 159220 said:The only scenario I can think of that would cause that is both a wrong-side failure on *all* the track circuits between the strike-in point and the crossing *and* a broken treadle. I presume somebody has determined that that is rare enough not to worry about. The failure alarm is raised for a number of possible reasons (for example, mains power failure or crossing down for more than 4 minutes). The SimSig AHB is based on the typical circuits found in the IRSE Red Book so you can experiment with it to get an idea of what can happen. Log in to reply |
| Setting a route over a level crossing 19/11/2024 at 09:07 #159234 | |
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kbarber
1764 posts |
clive in post 159233 said:<snip>I think it's accepted that absolute safety is impossible. I read somewhere that when SSI was being developed, the BR CS&TE (or perhaps the Railway Inspectorate) required the developers to show that the system would not give a wrong-side failure more than once in a million years. I imagine a simultaneous wrong-side TC failure (even more so if there was more than one TC between strike-in and crossing) and wrong-side treadle failure (given that treadles also will be designed to fail safe) was viewed as having a similar level of probability. Log in to reply |