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+----- Thread: 2006 Q5 - Permissive terminal platforms (/showthread.php?tid=1436)
2006 Q5 - Permissive terminal platforms - dorothy.pipet - 22-07-2013
Attempt for comments please.
I think I may not have put enough in the diagram to cover the 12 marks allocated, any suggestions on what I've missed?
RE: 2006 Q5 - Permissive terminal platforms - PJW - 22-07-2013
I think your diagram was good- to be honest I agree 12 marks seems a lot to allocate to just to a diagram, but I don't feel you missed anything essential off it. However I think I'd interpret "diagram" to include the "route box" style info as well within that allocation. hence ironically it might have been the "written" part that was too light.
Being picky I might have expected-
a) the subsidiary aspect (very old teminology- has been called PL for at least 20 years!) to have been drawn correctly- one dot should be in the right angled corner (bottom right when viewing the signal as a driver would) and and at 45 degrees up from that position - you have depicted at 90 degrees;
b) the smaller indicator is a "Miniature Alphanumeric Route Indicator" rather than a miniature aspect as you have stated;
c) although not strictly relevant to the answer, given you have drawn signals 1 & 3, it would have been good to have equipped signal 3 with a route indicator (even though only 1 route, it could appear to have one straight on and so I'd play safe);
d) I think I'd generally expect the incoming signal to have a Standard Alphanumeric Route Indicator for both platforms in this scenario- given that these are terminal platforms I would rather assume a blanket speed restriction in the station thoat area so no need for main aspect approach release.
You interpreted "controls on the incoming signal" more widely than I think I would have done- I think it was only really meaning the differences in track circuit proving within the route and the approach release strictly relevant to the differences, rather than the full controls- however you may well be correct, certainly as you gave less detail re the Lime St than might have been expected.
Couldn't find where you defined your note #1 for a long time when looking for it and gave up looking; it was only later when I looked at your part 2 that I found it, rather hidden in the text. The fact that it was considerably after #2 confused!
As you correctly identified, this queston is really about Lime Street Control; I think you are also right that it is rarely used in new work nowadays or indeed for many years. I can't think of a real project on which I have worked that has utilised, although to be fair I haven't worked on that many terminal ststions with permissive working at all.
I don't think it is anything to do with SSI; I think it does reflect the more or less total "multiple unit" railway that arose, similarly to SSI, in the mid / late 1980s, The original Lime Street controls were about distinguishing between a light loco being added to carriages and a complete short train and thus really associated with the "locomotive and carriages" railway. Slow speed multiple units had been around for quite a time, but I suppose that it wwas the introduction of the HST in the mid 1970s which was the start of fixed formation mainline express trains.
Similarly the whole idea of measuring tracks breaks down a bit, nowadays since drivers are instructed to stop a defensive driving distance back from a signal so that they can view it clearly- this tends to place the back of the train over the very joint placed with the intention of detecting it was short enough and thus defeats the purpose!
Hence whereas you didn't give all the detail that I think the examiners might have been expecting re full Lime Street controls, given both the context of the question and your stated rationale, then I think you gave plenty of info to justify good marks. You certainly demonstrated your knowledge and experience in the context of the question set and have answered it according to practices with which you are familiar, so despite it not being what I think they expected, it should still have scored very well.
You are right that the signaller is nowadays given the responsibility; you could have pointed out that computer systems such as TRUST allow them to find out precisely what rolling stock (down to actual vehicle numbers) are forming that service. Provided that the information input was accurate (and I am afraid that it isn't always) then at least they have the facts to determine whether a train will fit in a particular place- I think this is another reason why from the late 1980s such interlocking controls were no longer considered the best way of achieving as more sophisitcate information systems were being produced.
I am not sure if they have now solved it, but a few (perhaps 6) years ago Chiltern Railways had a problem at Marylebone- I think that they regularly needed to fit 3 short trains into the terminal platforms. Although I neither wrote the data nor tested it, I do feel that this may have been given Lime St controls originally- if so it would be one of the few SSIs to feature this I suspect. They seem to run a right mixture of 2-car, 3-car and 4-car units of two different classes but often paired up in a very adhoc mix-and-match way as available from the depot and not always accurately recorded. It seems that quite often what the signaller thought was coming from Aylesbury turned out to be something rather different when actually trying to get into the platform. Certainly there were various ideas of how to meaure a train on the move when it was still some miles out at Neasden so that the signaller could be given some aid when working out how to platorm it efficiently when it arrives a few minutes later. Not sure if it ever happened, but certainly would have been a "standalone" advisory system rather than an interlocking control.
All in all I am surprised that this question was asked as late as 2006; I'd have thought it would have been beyond its "sell-by date" by then.
(22-07-2013, 08:14 AM)dorothy.pipet Wrote: Attempt for comments please.
I think I may not have put enough in the diagram to cover the 12 marks allocated, any suggestions on what I've missed?