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| PoSA 09/07/2015 at 11:07 #74056 | |
clive
2789 posts |
" said:" said:I've just recalled a point that isn't addressed here.Entering a potentially obstructed block or a block with a possible broken rail. Calling-on and shunt moves are often signalled so that the line must be clear until just before the permissive area. For example, the last signal before a permissive platform will read over the station throat into the platform. Calling-on will require the throat tracks to be clear but the platform itself to be occupied. You can see this, for example, with the calling-on routes from signal 77 in WembleySub. Drivers will know that the calling-on aspect means the platform is occupied, not some random section of track before that. Similarly when a shunt aspect reads over complex trackwork into a yard (e.g. WS 18 to the TMD arrival road). PoSA, on the other hand, makes no guarantees about any track circuit on the route. The driver is being faced with an unusual situation, so it's a good idea to give them a different aspect. In particular, if you consider a through-station equivalent of the WS 77 example above (e.g. at Peterborough), it's a good idea to distinguish between "throat clear and train in platform" from "might be a train or a broken track in the throat or the platform". As for saying that the drivers should be taking care anyway, the whole history of signalling is about protecting the railway from mistakes made by humans who *should* have done something but got distracted, or got used to a particular way of things happening, or .... Log in to reply |
| PoSA 13/07/2015 at 06:40 #74173 | |
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clive
2789 posts |
" said:" said:Okay, a brief summary." said: All the signals were 3-aspect (later on two signals were changed to 4-aspect). At facing junctions there were two heads side-by-side (at different levels), except that the two Upminster Up Starters were each a single signal with a 4-case theatre aspect below. There were no repeater signals, no disc distants (the 3 aspects were deemed sufficient for main-line trains), and no "directing lights" signals. There was a marker light under the main aspect which was lit red when the main head was red or yellow and unlit when it was green (after a few years this was changed to only being lit when the main head was red). The marker was omitted when the next signal was a semaphore (the logic of this escapes me). If the signal was an automatic or a controlled signal in automatic mode, the same calling-on arrangement as the New Lines was used. If the signal was red, the berth TC had been occupied for 60 seconds, and the first overlap track circuit was clear, then the marker light went out and was replaced by a small yellow light (under the main red). The train could then proceed into an occupied section - possibly multiply occupied - without being tripped. At a later date the small yellow was changed to an illuminated "P" and the train *was* tripped on passing the signal. (This "P" indication was also added to the otherwise standard LU signalling between Campbell Road Junction and Barking.) My write-up of the New Lines signalling is here, though it hasn't been updated to address the points in this post. Last edited: 13/07/2015 at 06:41 by clive Log in to reply The following users said thank you: kbarber, Muzer |
| PoSA 13/07/2015 at 18:46 #74191 | |
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Jersey_Mike
250 posts |
" said:I don't think you get to play that card here. To avoid human error its best to be explicit as possible and a signal where a route is implied to be clear up to some "known" (but not marked?) point isn't very explicit. Now I know the European distinction between main and shunt movements, but I believe the cleaner system would be to collapse all such movement authorities into a single PoSA rule or add additional PoSA signals where drivers are entering potentially occupied sections. I guess it's too late to re-engineer the system, but flashing \ would be best entering low speed unoccupied blocks with a steady \ at the start of the occupied (or TC failed) area. Log in to reply |
| PoSA 13/07/2015 at 18:57 #74192 | |
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Danny252
1461 posts |
So you're suggesting a system where you're not even explicitly telling the driver whether or not his route is actually clear?
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| PoSA 13/07/2015 at 19:43 #74195 | |
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Hooverman
306 posts |
I thought this was all pretty simple. A subsidiary signal on a main aspect or ground level used for calling another train into an occupied section for the purpose of platform sharing or attaching, but either way draw forward as far a line is clear. A subsidiary signal either on main aspect or ground level for going into sidings, draw forward as far a line is clear. A POSA aspect which can only be used once you've used the 1st train to examine the line after passing the signal at danger in the usual way and confirming nothing untoward has been found. Is just used as a way to reduce radio coms for visual authority to pass a signal at danger do to signalling equipment failure and to drive at caution until the next signal. I can't see what is confusing about that. Log in to reply |
| PoSA 13/07/2015 at 19:45 #74196 | |
GeoffM
6377 posts |
" said:To avoid human error its best to be explicit as possible" said: I believe the cleaner system would be to collapse all such movement authorities into a single PoSA ruleContradiction much? SimSig Boss Log in to reply The following users said thank you: andyb0607, pedroathome |
| PoSA 14/07/2015 at 11:27 #74218 | |
block_operator
17 posts |
At this point, a short explanation of the situation in Germany might be interesting, since the German practice differs from most other railways. In Germany, almost every main signal is equipped with an subsidiary signal the signaller can switch on under staff responsibility to authorise a train to pass the signal at danger. In older interlocking systems (mechanical and powerframe boxes), that subsidiary signal can be switched on bypassing all interlocking functions. The operation of that signal is only automatically registered. So, the safety doesn't differ from a written order. The traditional German philosophy was that this subsidiary signal just replaces the written order to pass a main signal at danger. In modern interlocking systems, the signaller has two options to switch on a subsidiary signal for passing a signal at danger. By using the normal operation, the subsidiary signal will only clear after a locked route has been established. In contrast to a main route, it's sufficient to have all points locked the train will pass through. Locking of flank points and points in the overlap is not required, however. If a locked route cannot be set up for some reason, the signal may use a special command to clear the subsidiary signal under full staff responsibility like in the old systems. However, when doing so, the interlocking will force the signaller to switch off automatic point setting in the relevant area. To make it even more complicate, the are two types of subsidiary signals to authorise a train to pass a signal at danger: a) the replacement signal (German: Ersatzsignal) b) the caution signal (German: Vorsichtsignal) The replacement signal ('replacement' because it replaces a written order) authorises the driver to pass a signal at danger and to proceed without being required to run on sight. The signaller is in charge that all points are correctly set and that the line is clear. In the point zone beyond the signal, the driver must not exceed a speed of 40 km/h. The aspect of that signal is a flashing white light or, in older installations in the former Bundesbahn region, three small steady white lights in a triangle with top up. The caution signal authorises the driver to pass a signal at danger and to proceed cautiously on sight through the section up to the next main signal. The signaller is only in cahrge that all points are correctly set. The aspect of the caution signal is three steady yellow lights in a bottom-up triangle forming the letter V (for 'Vorsicht' = German for 'caution'). The interlocking control for both kinds of signals is the same. The interlocking doesn't 'know' whether a main signal is equipped with a) or b). A main signal may be equipped either with a) or with b) but never with both types. This is to prevent the signaller from erroneously clearing the replacement signal while he or she had to use the caution signal. Log in to reply The following user said thank you: Forest Pines |
| PoSA 14/07/2015 at 13:48 #74221 | |
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Jersey_Mike
250 posts |
In North American practice the notion of a "call on" is nothing that train crews ever have to care about because that is something that is only ever visible to the dispatcher. Any non-circuited or occupied piece of track automatically triggers a Restricting indication in the signal logic. Dispatchers or operators only request that a signal be displayed and the signaling logic provides the train crew with the best signal indication possible for the given circumstances. The one exception is where there is an occupied circuit within an interlocking. That is when a call on is requested by the dispatcher or operator. The train crew gets the same Restricting indication, it just takes an extra step to bring it up. Any complex terminal areas that were built with sufficient funds are equipped with platform entry signals so that a train can move through the points on a signal better than Restricting, even if the station track is already occupied (or not circuited). " said: " said:I'm referring to instructions to the driver. You are saying that the \ indication means different things depending on the context. Reducing everything to the same standard (expect occupied track) makes the instruction to the driver more explicit. (It also reduces the complexity of the interlocking logic). The Sweedish system of dwarf signals do a good job of being explicit in both instruction and context.To avoid human error its best to be explicit as possible" said:I believe the cleaner system would be to collapse all such movement authorities into a single PoSA ruleContradiction much? Log in to reply |
| PoSA 14/07/2015 at 14:21 #74223 | |
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Sacro
1171 posts |
" said:The Sweedish system of dwarf signals do a good job of being explicit in both instruction and context.That's a Daily Mail article about the hunting ban... :doh Last edited: 14/07/2015 at 14:21 by Sacro Log in to reply |
| PoSA 14/07/2015 at 14:33 #74224 | |
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TimTamToe
664 posts |
" said:" said:At least my cock up with having the Channel Tunnel opening 3 years earlier than it did regarding the WTT question in the other thread was at least close to the topic lolThe Sweedish system of dwarf signals do a good job of being explicit in both instruction and context.That's a Daily Mail article about the hunting ban... :doh Log in to reply |
is NOT allowed and the signaller wants the security of the route locking before allowing the movement to begin.