2009 Q3 - Aspects and indications

[dorothy.pipet]

An attempt for comments please.

[PJW]

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.

An attempt for comments please.

[dorothy.pipet]

Amazingly I spent about 30 mins on this, although there was an interuption which probably equates to extra thinking time! I had my notes open to check a few things but the question would have been a gift for me in an exam.

I became aware later that the signal spacing bit was in the wrong section. In an exam would it gain any marks for part 3, perhaps if I added a note indicating I realised it was in the wrong place?

The definition of a green aspect came directly from err.... something I read somewhere. Probably the IRSE Green or Red text books. I do see your point, it needs rephrasing.

[PJW]

I think that the examiners would, provided of course they noticed it initially, give some credit for something that they realised was absent when later reviewing the last section. Howeverif you as the candidate notice, then it would be wish to ring portion, annotate with # and arrow downwrds.......then in the last section can put: "# from section 1". Maximises your chances of getting the credit.

Instead in that first section could possibly have mentioned splitting distants, Preliminary Route Indicators and even banner signal.

Amazingly I spent about 30 mins on this, although there was an interuption which probably equates to extra thinking time! I had my notes open to check a few things but the question would have been a gift for me in an exam.

I became aware later that the signal spacing bit was in the wrong section. In an exam would it gain any marks for part 3, perhaps if I added a note indicating I realised it was in the wrong place?

The definition of a green aspect came directly from err.... something I read somewhere. Probably the IRSE Green or Red text books. I do see your point, it needs rephrasing.

[asrisaku]

Hi

Another attempt with a friend review. Any review is welcome

Best regards, Arnut

[PJW]

I think 2009 was the first year of the non-appearance of the aspect sequence chart that had become an established exam favourite.
I remember that the examiners said that very many candidates almost completely ignored the initial part of the question and so your good presentation would have been viewed very favourably and may actually have scored 4.5 or even 5/7.
However I do agree with the comments given
a) state the railway's practice being described,
b) you didn't really "describe"- particularly the GPL / LOS needed some words re colour and aspects displayed
c) were weak re the "meaning to the driver". Y means "be prepared to stop at next signal"; "YY means "be prepared to find ext signal at Y", Whereas to a signal engineer then the aspect sequence diagram depicts this, it is not how a driver would think of it.

I agree also that you did poorly on the next part. The sort of things that you should have mentioned

1. A PLJI can be misread particularly at night, partly because of its vertical separation from the Y (or the G of a 4 aspect signal); a PLJI pos1 can seem to be a PLJI pos6 and similarly pos2/pos5 and pos3/pos4 since the angles are the same. Hence we do try to avoid using both of a pair at any one signal whenever we can, thus effectively limiting to 3 PLJI on a signal.

2. Until some 20 years ago we would utilise a SARI provided for a main aspect also for the PL to the same destination on the basis that the aspect declared the class of route and the SARI just giving the destination. However it was found that there was some drive confusion as if expecting a Y plus SARI then on seeing that SARI that was the aspect that they remembered getting even when actually the signal was at R with PL. Nowadays we provide a separate MARI to utilise with the PL to avoid this.

3. When a driver has to look at many different elements of a signal to determine the full meaning then it is a harder cognitive task; we need to give a greater time (and therefore distance) for the driver to do this for "complex" signals- it increases the Minimum Reading Time.

4. You certainly need to mention the relative visibility of all elements of a signal's display. If PLJI comes into sight after the main aspect (it is higher and may be obstructed due to a road over-bridge on the approach to the signal) then the driver may see a Green and therefore not brake yet only later become aware that it is qualified by a PLJI needing them to slow to respect a diverging route speed. Hence we need to take this into account and where necessary impose more restrictive Approach Release.

5. The other factor re mixing can be the relative brightness / range of the various elements- for example the SARI is only readable over a range of about half of that of a main aspect and the SARI much less so. Therefore the SARI is well paired with the PL and the SARI can only be used with a main aspect when the approach speed for the diverging route is reasonably low whereas a PLJI is used for the maximum range and thus best for the highest speed divergences.

6. You could talk about a "splitting distant" signal- it has two heads side by side to reflect the diverging junction one signal section ahead. It is theoretically very good at conveying the info that the driver needs to know, BUT it is wide and so hard to position wrt structure gauge and also if the visibility of one of the heads becomes obstructed (perhaps by the overhead line vertical masts if there is a curved approach) then there is a risk that it can be misread / misinterpreted.

The last section did need more in the way of risks and you should have explicitly related at least one to "driver anticipation", one to "confusion", one arising from "imposition of signalling controls" and one resulting from "movement of other trains".
Definitely should have talked about approach release for junctions (MAR particularly but if you know about MAY-YY then that is an even better example of a "lie" to the driver). Certainly you were on the right lines when talking about repeated double yellows- this can just be the result of one train following another at broadly similar speed and driver getting so used to it that not actually braking at the YY but just anticipating that the next one will be YY by time they arrive at it- up until the day when of course it is still at Y the 2nd train still doing almost maximum speed and there only being half braking distance to the train ahead that may be stationery. However we still in extremis design a sequence having "consecutive double yellows" and that also can give similar result.

Could also have mentioned flashing yellows and the precautions we take to make sure that the driver is given a long enough time to observe that the signal really is flashing properly rather than just a steady yellow suffering from interrupted sighting whilst being approached.

Hence I largely agree with the marks; it was a pass but only just. What you wrote was good as far as it went being very largely accurate and very neatly and well presented, but suffered by not always fully addressing the core of the question asked.

If you haven't looked at already then I also suggest you look at the previous attempt at this question higher up this thread and the comments made on it.

PJW

Hi

Another attempt with a friend review. Any review is welcome

Best regards, Arnut

[asrisaku]

Thanks for your time and your advice. To be honor with you, I am building up the knowledge and somehow cannot think through and because of insufficient knowledge of experience operation, maintenance and etc. The given comments will probably help trigger my mind to rethink the way to answer and develop my thinking process.

[PJW]

It certainly appears that you have a pretty good grasp of UK mainline railway signalling; there are many in the UK signalling industry who have far worse knowledge. This indeed is essential underpinning information needed for the IRSE Exam, but it deliberately goes beyond that and requires candidates to demonstrate a fuller understanding that can really only be built up by experience. This is where a significant number of years undertaking a variety of roles is extremely useful. However you are right and part of it is critically examining the question to determine precisely what it means and to work-out why it has been asked in the way it has and this is certainly a skill that gets honed with practice.

Thanks for your time and your advice. To be honor with you, I am building up the knowledge and somehow cannot think through and because of insufficient knowledge of experience operation, maintenance and etc. The given comments will probably help trigger my mind to rethink the way to answer and develop my thinking process.