Page1:
A few niggles: Green surely means more than next signal at proceed- G to Y in a 4 aspect sequence is not acceptable. Probably better not to refer to the following aspect at all but say something like "clear, no signalling restriction, continue at a maximum speed determined by forthcoming speed profile of the line whilst also respecting maximum speed of the rolling stock"[i]
This is actually quite important as it relies on driver's route knowledge in the UK; in other railway signalling systems the signal aspects oftengive the maximum speed (so a loop exit signal reading over slow speed points would give an aspect relevant to that speed whereas in the UK an unrestricted aspect would be shown).
[i] As an aside it will be interesting whether something related to this could be involved in the recent high speed derailment in Spain. It seems to have happened pretty soon having transitioned onto legacy signalling having been on a high speed line ioperated by ETCS. There is a possibility that the driver needed to brake for the restriction when in ETCS mode; the question is whether the ETCS was configured to reflect this need to brake and whether any legacy reminder that there may have been (in the UK that would be the AWI and associated AWS) had been removed when ETCS was commissioned.......It will be very interesting to find out if there was actually more to it that just "driver error"- my guess is that there will turn out to be some other factor but whether my hunch is right is another question....
Alsio being picky, the flashing aspects give advance warning of a divergence at one (single FY) and two (double FY) signals ahead- as worded could be read to be at the signal at which displayed!
The rest of it seems spot on; you could probably have got away with slightly less detail re route indics but if you could do in 7 mins then that was excellent.
Page 2:
Not convinced that your first section actually addressed the question asked. I read the question re "combining aspects and indiications" but I suppose that you might be thinking that it could mean that the overall Signalling Plan design "combines the aspect displayed at one signal with the one displayed at the next". Your strongest claim is the desire not to have one signal giving the first caution for two separate stopping places; I do have even more difficulty in stretching the question to include the regularity of signal spacing. Also UK mainline practice does not have 2 aspect signalling (although I accept it does at its boundaries with LU, Tyne & Wear metro etc); it has 2 aspect signals R/G and Y/G but these are used in conjunction with each other as "isolated 3 aspect signalling" so there is no transition consideration to 3 aspect MAS.
Hence I would have put your first heading last instead, just talked about evenness of spacing and felt the need to "sell" its applicability to the examiner by explicitly "echoing" the question wording:
"Finally it must be remembered that a driver sees a succession of signals and forms a composite mental picture by the combination of each the observed signals.....". This is powerfully saying "I have read your question and I am claiming that this is a valid interpretation- I dare you not to give me credit for this; you know that I haven't just gone off on a tangent carelessly!"
Rest was fine.
However explaining why the driver might get confused would get you better marks than just stating it. Could have added that the PLJI issue is principally a problem at night where not much ambient light- the problem is that the driver loses visual clues with which to align the PLJI compared to the lit aspect. Actually not really a problem with a 3 aspect Dorman "searchlight"; it is a conventional 4 aspect signal when displaying single yellow that is the worst case.
Page 3:
Fine.
[Personally I have never been convinced about the need to provide MARI to associate with the PL in addition to the SARI with the main aspects.
Admit to being biased, having been scarrred for life by the infamous "Bell Mods" c1996 that arrived like a deluge on the Stratford commissioning. In the month prior to major commissioning we had lots of SSI data changes, almost all the TFM plucouplers in the station area within what were partially commissioned locs had to be opened up (to add and change wiring), quite often new TFMs were also needed, occasionally even in new loc case and of course power busbar and datalink changes. Then we had to redo all the through testing that had been completed- other unrelated functions also had to get moved around just to free up the input 6's that suddenly were needed for more current proving inputs.......
And what precisely was the risk we were avoiding by doing all this? In case a driver just looked at the SARI (or ARI as it was called in those days) and thought- that means the platform is empty, I shall not bother to observe that the yellow is not lit, but the PL is lit and I will happily pass the red and not expect to find a train in the platform, just because after all I got a large route indicator like I do when the Red is off and the Yellow lit so it must mean the same!]
Page 4/5:
Actually I think this would have been a better place than the initial part to talk about the evenness of signal spacing, aspect sequence transitions from having been used to getting 2 warning signal approaching the red to then the yellow meaning full braking distance, signal being a first caution for two sepaate red aspect.
Aspect sequence anticipation confusion- could have said more re the flashing sequence (needing to see enough of the flahing yellow to realise that truly flashing aspect not just brief interruptions in sighting etc, avoidance of a failure scenario in which flashing seqence initiates, collapses, tries again ad infinitum).
Also could have talked about the inherent lie which is MAY-YY and how the introduction of better performing rolling stock can lead this to being exposed and the signal enfgineer embarassed- to an extent this is always a consideration when "attainable speed" is involved.
Overall though I think was extremely good and I guess would be "head and shoulders" above most offerings that would have been received.
I think that you probably spent too long on the middle portion compared to the last portion which had 50 percent more marks; I guess that you didn't complete this in 30 mins and it would have been a shame to have lost anything from pages 4 & 5 because you ran out of time having spent too much on the section before.
However if you could do this in the time in exam conditions, I am pretty sure that this would have been a Distinction.
A few niggles: Green surely means more than next signal at proceed- G to Y in a 4 aspect sequence is not acceptable. Probably better not to refer to the following aspect at all but say something like "clear, no signalling restriction, continue at a maximum speed determined by forthcoming speed profile of the line whilst also respecting maximum speed of the rolling stock"[i]
This is actually quite important as it relies on driver's route knowledge in the UK; in other railway signalling systems the signal aspects oftengive the maximum speed (so a loop exit signal reading over slow speed points would give an aspect relevant to that speed whereas in the UK an unrestricted aspect would be shown).
[i] As an aside it will be interesting whether something related to this could be involved in the recent high speed derailment in Spain. It seems to have happened pretty soon having transitioned onto legacy signalling having been on a high speed line ioperated by ETCS. There is a possibility that the driver needed to brake for the restriction when in ETCS mode; the question is whether the ETCS was configured to reflect this need to brake and whether any legacy reminder that there may have been (in the UK that would be the AWI and associated AWS) had been removed when ETCS was commissioned.......It will be very interesting to find out if there was actually more to it that just "driver error"- my guess is that there will turn out to be some other factor but whether my hunch is right is another question....
Alsio being picky, the flashing aspects give advance warning of a divergence at one (single FY) and two (double FY) signals ahead- as worded could be read to be at the signal at which displayed!
The rest of it seems spot on; you could probably have got away with slightly less detail re route indics but if you could do in 7 mins then that was excellent.
Page 2:
Not convinced that your first section actually addressed the question asked. I read the question re "combining aspects and indiications" but I suppose that you might be thinking that it could mean that the overall Signalling Plan design "combines the aspect displayed at one signal with the one displayed at the next". Your strongest claim is the desire not to have one signal giving the first caution for two separate stopping places; I do have even more difficulty in stretching the question to include the regularity of signal spacing. Also UK mainline practice does not have 2 aspect signalling (although I accept it does at its boundaries with LU, Tyne & Wear metro etc); it has 2 aspect signals R/G and Y/G but these are used in conjunction with each other as "isolated 3 aspect signalling" so there is no transition consideration to 3 aspect MAS.
Hence I would have put your first heading last instead, just talked about evenness of spacing and felt the need to "sell" its applicability to the examiner by explicitly "echoing" the question wording:
"Finally it must be remembered that a driver sees a succession of signals and forms a composite mental picture by the combination of each the observed signals.....". This is powerfully saying "I have read your question and I am claiming that this is a valid interpretation- I dare you not to give me credit for this; you know that I haven't just gone off on a tangent carelessly!"
Rest was fine.
However explaining why the driver might get confused would get you better marks than just stating it. Could have added that the PLJI issue is principally a problem at night where not much ambient light- the problem is that the driver loses visual clues with which to align the PLJI compared to the lit aspect. Actually not really a problem with a 3 aspect Dorman "searchlight"; it is a conventional 4 aspect signal when displaying single yellow that is the worst case.
Page 3:
Fine.
[Personally I have never been convinced about the need to provide MARI to associate with the PL in addition to the SARI with the main aspects.
Admit to being biased, having been scarrred for life by the infamous "Bell Mods" c1996 that arrived like a deluge on the Stratford commissioning. In the month prior to major commissioning we had lots of SSI data changes, almost all the TFM plucouplers in the station area within what were partially commissioned locs had to be opened up (to add and change wiring), quite often new TFMs were also needed, occasionally even in new loc case and of course power busbar and datalink changes. Then we had to redo all the through testing that had been completed- other unrelated functions also had to get moved around just to free up the input 6's that suddenly were needed for more current proving inputs.......
And what precisely was the risk we were avoiding by doing all this? In case a driver just looked at the SARI (or ARI as it was called in those days) and thought- that means the platform is empty, I shall not bother to observe that the yellow is not lit, but the PL is lit and I will happily pass the red and not expect to find a train in the platform, just because after all I got a large route indicator like I do when the Red is off and the Yellow lit so it must mean the same!]
Page 4/5:
Actually I think this would have been a better place than the initial part to talk about the evenness of signal spacing, aspect sequence transitions from having been used to getting 2 warning signal approaching the red to then the yellow meaning full braking distance, signal being a first caution for two sepaate red aspect.
Aspect sequence anticipation confusion- could have said more re the flashing sequence (needing to see enough of the flahing yellow to realise that truly flashing aspect not just brief interruptions in sighting etc, avoidance of a failure scenario in which flashing seqence initiates, collapses, tries again ad infinitum).
Also could have talked about the inherent lie which is MAY-YY and how the introduction of better performing rolling stock can lead this to being exposed and the signal enfgineer embarassed- to an extent this is always a consideration when "attainable speed" is involved.
Overall though I think was extremely good and I guess would be "head and shoulders" above most offerings that would have been received.
I think that you probably spent too long on the middle portion compared to the last portion which had 50 percent more marks; I guess that you didn't complete this in 30 mins and it would have been a shame to have lost anything from pages 4 & 5 because you ran out of time having spent too much on the section before.
However if you could do this in the time in exam conditions, I am pretty sure that this would have been a Distinction.
(31-07-2013, 12:39 PM)dorothy.pipet Wrote: An attempt for comments please.
PJW