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Post by jammers on Jan 2, 2011 13:01:24 GMT
I notice that on the westbound platform there is a signal two thirds of the way down the platform - more often than not trains entering the platform actually stop just before the signal goes green and then they crawl to the end of the platform.
I assume this signal is here to stop trains entering the station too quickly. However, at Moorgate the trains have just come round a rather sharp bend and aren't going particularly fast anyway. From the eastbound direction trains enter the platform much quicker and there is no signal to slow them down.
Can someone explain please, thanks.
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metman
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Post by metman on Jan 2, 2011 14:55:48 GMT
I believe it is part of the protection for the juction ahead. There is a similar situation at Baker Street heading East (Plat 3 and 5). It is to ensure that if a train does overrun it is within the safe overrun distance.
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mrfs42
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Post by mrfs42 on Jan 2, 2011 15:25:18 GMT
OE 260 is there to provide protection when there is something going in or out of the bays as a crawler signal.
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Colin
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Post by Colin on Jan 2, 2011 18:23:42 GMT
Or more properly known as a draw up signal - as stated though, it'll be there to help protect the junction ahead [which is closer than ideal].
Generically speaking, a draw up signal works by showing a red and yellow aspect together to indicate to the driver that their speed is being checked.
When their speed is proved to be low enough (usually 10mph), the signal will "clear" to single yellow. Should the starter be green, or become green, the speed check becomes irrelevant and the draw up will also show green.
Of course there are variations of how exactly each draw up works all over the combine, depending very much on the local requirements and reasons for installing such signals; but they are very much a part of a drivers route knowledge so there should be no excuse whatsoever for not knowing the signal is there or how it works.
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rincew1nd
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Post by rincew1nd on Jan 2, 2011 18:26:54 GMT
So are draw-up signal the exception to the rule where the repeater signal is lit when the stop/go signal is showing stop?
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Colin
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Post by Colin on Jan 2, 2011 18:33:30 GMT
Repeater? There can be a repeater before the draw up, but that will only show red or green - more often than not it'll usually be red but it depends on how a particular given draw up works and/or what it's protecting, and whether or not it's associated starter is cleared.
Draw up's have three aspects and can show two aspects together routinely as part of their operation (red & yellow only).
Is that what you are asking? Does that make sense?
EDIT: I suspect a series of diagrams may be required.....
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Post by jammers on Jan 2, 2011 18:34:49 GMT
Thanks for the interesting replies - at the weekend when the other Moorgate platforms out of use would it not make more sense for it to just show green?
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Colin
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Post by Colin on Jan 2, 2011 18:36:21 GMT
You'll need someone like Harsig or MetControl to see this thread and reply as they know exactly how the Moorgate area signalling is set up...
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mrfs42
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Post by mrfs42 on Jan 2, 2011 18:54:53 GMT
Is the ∆ still in track 240B or is it now a PD as part of the S stock enabling works?
IIRC some of the TCs around that area were coded to get round any induced spikiness from the OHLE next door; single code only.
WRT to jammers second question I'd have thought it'd be a waste of a lot of peoples time in modifying the circuit, as draw-ups (sorry for using the ancient name upthread) are generally sited where trains are braking to a stand - they aren't used as headway splitters: if there is a current nstance of a draw-up used in that sense I'd be interested to know.
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rincew1nd
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Post by rincew1nd on Jan 2, 2011 19:10:10 GMT
Draw up's have three aspects and can show two aspects together routinely as part of their operation Sorry, my bad I was forgetting draw-ups are different to the usual two aspect malarky. |
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Post by citysig on Jan 2, 2011 20:24:32 GMT
You'll need someone like Harsig or MetControl to see this thread and reply as they know exactly how the Moorgate area signalling is set up... And I have seen it - although I'm more the "simply speaking" side of things. For anything more in depth like relay set ups and whether the blue wire connected to the green wire makes everything tick, you'll still have to see someone of the calibre of Harsig or one of the many signal technical side people here... In the case of the example at Moorgate and at other locations, Colin more or less summed up how it all works in his first reply. Signal OE260 does indeed protect the junction in advance of the station - that junction being where the lines to/from the bay platforms 3 & 4 join the main. The reason it is there is due to the fact that should a train pass the station starter - OE26 - there is the risk that although the train will be "tripped" it could still foul the junction once it has come to a stand. Regardless of whether a train is arriving/departing one of the bay platforms or not, if signal OE26 (starter) is at danger, then OE260 will operate as a "draw-up" and will force a train's speed to be reduced before it clears to yellow. If signal OE26 is cleared to green, then signal OE260 will also show a green aspect and no speed reduction will be necessary. At Baker Street, provided the junction ahead is set for a train to depart platform 5, then the draw-up will clear to yellow much sooner - in fact as early as when the train has just left Edgware Road. This is based on the fact that the junction and therefor the overlap is available to the approaching train, and the need to protect the junction by reducing the speed of the train is less. To be honest I cannot recall if Moorgate has this facility - from memory I don't think it operates any quicker even if the junction is clear. Someone will need to confirm. As we've mentioned draw-up and speed controlled signalling in general, some of you will be very interested in what Edgware Road is to get under the S7 project. Put simply, a whole series of variable speed limits, variable overlaps and signals that will enable some of the old flexibility that Edgware Road once had to return - whilst being able to accommodate S7 trains. |
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Post by North End on Jan 2, 2011 21:40:16 GMT
Or more properly known as a draw up signal - as stated though, it'll be there to help protect the junction ahead [which is closer than ideal]. Generically speaking, a draw up signal works by showing a red and yellow aspect together to indicate to the driver that their speed is being checked. When their speed is proved to be low enough (usually 10mph), the signal will "clear" to single yellow. Should the starter be green, or become green, the speed check becomes irrelevant and the draw up will also show green. Of course there are variations of how exactly each draw up works all over the combine, depending very much on the local requirements and reasons for installing such signals; but they are very much a part of a drivers route knowledge so there should be no excuse whatsoever for not knowing the signal is there or how it works. Locations where the red/yellow illuminate together are very rare. I believe the only such examples are Whitechapel, Camden Town, and possibly Golders Green. (Also A.325 Lambeth Nth - Elephant & Castle, different setup there though). In the case of Moorgate, when the site was controlled by Farringdon signal cabin, I believe Moorgate was normally left in automatic through working and so the draw up would clear as soon as the section ahead was clear. When control was transferred to Baker Street, the route became set by computer, therefore the draw up now stays at red until the route from the starter is called. |
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Tom
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Post by Tom on Jan 2, 2011 23:24:26 GMT
Is the ∆ still in track 240 B or is it now a PD as part of the S stock enabling works? IIRC some of the TCs around that area were coded to get round any induced spikiness from the OHLE next door; single code only. I believe it's now a PD. All the tracks from Moorgate platforms and west therof towards King's X are of the 1978 Coded Variety. In the case of Moorgate, when the site was controlled by Farringdon signal cabin, I believe Moorgate was normally left in automatic through working and so the draw up would clear as soon as the section ahead was clear. When control was transferred to Baker Street, the route became set by computer, therefore the draw up now stays at red until the route from the starter is called. That's my understanding too. What I can't remember is if a Platform Timing Section was provided for OE26 at the same time as computer control was introduced which would account for OE260 often only stepping up to yellow most of the time. I knw a number of other sites gained platform timers as part of or around the same time as the Met City project. |
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North End
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Post by North End on Jan 2, 2011 23:44:23 GMT
Is the ∆ still in track 240 B or is it now a PD as part of the S stock enabling works? IIRC some of the TCs around that area were coded to get round any induced spikiness from the OHLE next door; single code only. I believe it's now a PD. All the tracks from Moorgate platforms and west therof towards King's X are of the 1978 Coded Variety. In the case of Moorgate, when the site was controlled by Farringdon signal cabin, I believe Moorgate was normally left in automatic through working and so the draw up would clear as soon as the section ahead was clear. When control was transferred to Baker Street, the route became set by computer, therefore the draw up now stays at red until the route from the starter is called. That's my understanding too. What I can't remember is if a Platform Timing Section was provided for OE26 at the same time as computer control was introduced which would account for OE260 often only stepping up to yellow most of the time. I knw a number of other sites gained platform timers as part of or around the same time as the Met City project. I'm fairly sure OE.26 doesn't have a timing section, but I could be misremembering. Shouldn't be too hard to find out! |
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mrfs42
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Post by mrfs42 on Jan 2, 2011 23:51:03 GMT
I'm fairly sure OE.26 doesn't have a timing section, but I could be misremembering. Shouldn't be too hard to find out! OE 26 doesn't IIRC; OE 260 has a 4.5sec ∆/PD. I've always been a wee bit puzzled by the requirement for OE 28 and OE 29 (Bay starters) to have been at danger - not for the other one, for themselves; a change from the 'not normal' note, I suppose. |
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Tom
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Post by Tom on Jan 3, 2011 0:58:35 GMT
At Baker Street, provided the junction ahead is set for a train to depart platform 5, then the draw-up will clear to yellow much sooner - in fact as early as when the train has just left Edgware Road. This is based on the fact that the junction and therefor the overlap is available to the approaching train, and the need to protect the junction by reducing the speed of the train is less. To be honest I cannot recall if Moorgate has this facility - from memory I don't think it operates any quicker even if the junction is clear. Someone will need to confirm. It does, OE260 can clear by the following means: To yellow with a short starter overlap available and ∆ 240 B operated for 4.5 secs or to yellow with a full speed overlap available and 26 lever reverse or to green with OE26 clear. I suspect because OE26 route call will require 'Control Tracks Clear' (ie. everything except the overlap of the next signal clear), we don't see the second method of clearing to yellow under normal circumstances. However, working the frame manually it is still achieveable, or at least it was last time I was down there in 2008. |
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Post by Harsig on Jan 3, 2011 10:08:31 GMT
It does, OE260 can clear by the following means: To yellow with a short starter overlap available and ∆ 240 B operated for 4.5 secs or to yellow with a full speed overlap available and 26 lever reverse or to green with OE26 clear. If traffic on the westbound from Aldgate is heavy I often manually select the route for OE26 as soon as the previous train has departed. This in turn allows OE260 to clear to yellow with a full speed overlap because 26 lever is reverse. Thus a following train can enter the westbound platform at higher speed. This in turn allows the starter at Liverpool St to clear a bit sooner, allowing a third train to get away from that station a bit sooner, so that the fourth train can move forward into Liverpool St and thus allow me to signal another train away from Aldgate at the earliest possible moment. |
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PGtrips
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Post by PGtrips on Mar 4, 2011 14:26:48 GMT
There is a very interesting accident report here www.railwaysarchive.co.uk/docsummary.php?docID=1402 pertaining to a collision at Faringdon in 1939 which clearly illustrates how the process of signalling development, including draw up signals, has been influenced by the need to guard against adverse operating incidents being repeated. It serves to illustrate how the overlap on a starting signal was inadequate for a train starting halfway down the platform - obviously not a problem that could occur now, but running in at too high a speed could without the aforementioned protection. A most interesting read. |
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