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| Standoffs and junctions without passing loops 11/01/2017 at 05:41 #91440 | |
Hawk777
386 posts |
Hello all! I have been reading through the UK signalling rulebook which someone posted a while ago, and also thinking about track layouts and designs. I was wondering something, in the context of non-fully-track-circuited working (e.g. block instruments, tokens, tokenless block, etc.): are there any examples of a signalbox that doesn’t have any passing capabilities? Perhaps it just oversees a junction in the middle of single line? If so, what provisions are made to prevent standoffs from happening? If it were only one box it would be pretty easy: once you accept a train from one side, don’t accept one from the other side until you’ve disposed of the one you have. But what if there were two non-passing-capable boxes in a row? Each one could accept a train towards itself, but as they tried to send them on down the line, the trains would come head to head and get stuck. Is this something that the UK rail network avoided by just not building track in that shape? Or did this ever happen, and were there special rules to avoid the problem?
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| Standoffs and junctions without passing loops 11/01/2017 at 08:40 #91442 | |
headshot119
4869 posts |
Pantyffynnon signalbox (south end of the Central Wales line) is such an example of this. It controls a section of single line with a junction facing to trains approaching from Port Talbot panel. If you don't follow the instructions you can in theory end up with three trains having a Mexican stand off. Before a train can be accepted from Port Talbot either the token section to Llanedeilo must be clear if it's heading towards Craven Arms, or the Gawun-cae-Gurwen branch must be clear if it's heading that way. And of course if you accept a train coming from either of these towards Port Talbot the line must be clear through. When the remote loops at Knighton and Llandovery were out of use, it was possible to accept two trains towards a loop that no longer existed! "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 |
| Standoffs and junctions without passing loops 11/01/2017 at 10:04 #91444 | |
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clive
2789 posts |
Originally the Railway Inspectorate wouldn't approve a layout like this. If there are sidings in the middle of a single line section, either an Annetts Key on the token/staff is used to unlock them, or there's a block instrument at the sidings that can be used to replace the token to allow another train through. I would expect the token instruments to be interlocked so that you can't create such a stand-off. So, suppose J is a facing junction so that trains from A can run to either B or C. The machines at B are locked whenever A has issued a token that hasn't yet been replaced, but not if J has issued a token from the A-J machine; similarly in the other direction. But no doubt it will turn out that there are real layouts that don't do this. Or the "locking" is done by Signal Box Instructions. Log in to reply |
| Standoffs and junctions without passing loops 11/01/2017 at 11:07 #91447 | |
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Danny252
1461 posts |
To go slightly off on a tangent, I can think of many examples where a box could not pass two passenger trains (loops/sidings not signalled for passenger use), but did have facilities to pass a passenger and a goods train.
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| Standoffs and junctions without passing loops 11/01/2017 at 12:36 #91450 | |
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headshot119
4869 posts |
clive in post 91444 said:Originally the Railway Inspectorate wouldn't approve a layout like this.As I've explained above it's quite possible to create a Mexican at Pantyffynon. All the prevention is by the signaller. "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 |
| Standoffs and junctions without passing loops 12/01/2017 at 03:41 #91484 | |
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Hawk777
386 posts |
OK, from what I’ve heard so far it sounds like there’s no standardized system; rather, it’s up to the SBSIs in each location to dictate procedures or the signallers to just be sensible. Thanks for the info!
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| Standoffs and junctions without passing loops 12/01/2017 at 09:30 #91486 | |
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kbarber
1742 posts |
Hawk777 in post 91484 said:OK, from what I’ve heard so far it sounds like there’s no standardized system; rather, it’s up to the SBSIs in each location to dictate procedures or the signallers to just be sensible. Thanks for the info!Or in some cases there was indeed interlocking. A Pictorial Record of LNER Constituent Signalling (A MacLean) gives the example of Brunstane Park (NBR), where the single line split into three. All sections were worked by Sykes Non-token Block and instruments were interlocked so it wasn't possible to accept from all directions simultaneously; interestingly, as I understand it you could accept on any 3 of the 4 instruments, with trains having to shunt onto the unoccupied line to clear each other if you needed to resolve a Mexican (and I've an idea that was the approved way of working the job). But I think this was also a goods-only branch, so many normal restrictions might be treated rather more lightly. Log in to reply The following user said thank you: Hawk777 |