2007 Q6 PLATFORM STARTER SPAD

[jbrownhill]

The York study group were set question 2 plus one other from the 2007 paper. Attached are my attempts at question 2 and question 6.
Any feedback would be appreciated to discuss at the next session.

[PJW]

The York study group were set question 2 plus one other from the 2007 paper. Attached are my attempts at question 2 and question 6.
Any feedback would be appreciated to discuss at the next session.

There are 18 marks for the first bit; so at first sight presumably we are looking for
a) a list of 9 relevant factors with mitigating measures, or perhaps
b) a shorter list covering 6 in rather more detail and therefore justifying 3 marks apiece (be that 1.5+1.5 by explaining more or 1+2 by having more than one possible mitigation for a given cause). Your answer had 7 causes / mitigations set out clearly but was rather light, so doubt whether you'd have got a full mark for each of the 14 items.

A couple of specific comments re:
i). With points 5 where they are, I certainly interpret the signal to be effectively at the end of the platform- however I do think the fact that the driver may need to get very close to it to get the full train into the platform could be a salient factor, but this is really your item ii). Would i be possible to move the signal closer to the point tips; given the fact that you need a block joint then it really doesn't seem likely to be possible to me.

iii) Suggest you need to say why the sub being hard to see would cause a SPAD; presumably you mean that the driver's view may not be good and difficult to see whether or not it is off and therefore if the driver has the expectation that it would be off then they see "what they want to see". However since the red is likely to be as close to the driver as practicable, offsetting the sub would need to be the left and thus likely to be harder to see.

Otherwise what you wrote looked OK. I think however that you definitely should have stated some assumptions; apart from anything else the question EXPLICITLY asked you to do so.
I think I'd have started with the assumptions regarding the sort of SPAD which was occurring; i.e. do they occur as a train is arriving (running SPAD) or after having stopped at the station (Start Away SPAD)? I actually would have expected the latter to be the more likely.
Certainly I think it is reasonable to believe on a metro that all trains would stop at station B- even if some pass through other stations non-stop, it does seem unlikely to occur at a station where 50% of trains actually end their journey.
Metros don't necessarily only have one type / length of train running on a line, but this is typical. However given that you want to include varying stopping positions in your iv), then you better state some assumption to justify that.
Similarly an assumption could be that it is the trains destined for the turnback which are those prone to SPAD; alternatively that it is those that are due to continue to C. By exploring these as possibilities one would ask oneself why signal 2 would be at danger in each scenario as perhaps at first sight this doesn't seem particularly likely. If however we assumed that signal 3 had to be positioned to permit the rear of a train waiting at it to be just clear of points 5, then it may well be that its overlap extends into the platform of the next station C. Hence if two consecutive trains were to run through to C then the second may well encounter signal 2 at red when it had finished its platform dwell, whereas this wouldn't be a usual situation when the trains were running through and terminating in the turnback strictly alternately. In the other scenario then why wouldn't the sub to the turnback have already cleared; the most likely reason I can deduce is that points 5 may be locked normal until the train has timed to a stand at signal 2 and it is then dependent upon the signaller recognising this and then setting the route into the siding; if the workload at the signalbox is busy then on occasion may not get around to doing it before the train has unloaded all passengers and platform staff / train CCTV satisfy driver that train is empty which may perhaps provoke starting the train almost as a reflex reaction. If the locking permitted signal 1 to be routed to signal 2 simultaneously with signal 2 into the siding, then it is hard to conceive how 2 could be at red (an essential pre-requisite for a SPAD!)- hence stating an assumption about the locking is valuable as it gives you a scenario to discuss that otherwise would be improbable.

The bit of the first question you failed to address in your answer was service pattern; I think that it is important to talk about "probability that the signal is at red", "driver expectation re aspect based on previous experiences" and also "departures from the norm"; I have included some of this in the previous paragraph.

So in outline that's how I think you'd aim to get your first 18 marks; in general I'd aim for 6 different causes each with a mitigation and supported by an associated assumption which makes the SPAD scenario plausible.

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For the last part you have 6 factors, all pretty brief so you couldn't really expect to get a mark for each. Some I think you do give just enough, but I'd advise fuller explanation.

In particular for example,
expand "signalling faults" to read: "technical SPADs occurring following aspect reversion resulting from a signalling fault such as track circuit showing occupied when clear, a loose link in aspect relay circuit etc".
Similarly "in cab ergonomics" is too vague- back it up with an example such as "cab sight line restricting view of close signals" or "lack of control over heating and ventilation leading to driver drowsiness".

To make up your 7th then what about "braking difficulties created by poor adhesion conditions resulting from wet/icy rails or contaminants such as leaves/ oil".

Overall given the fact that you gave an answer in less than a page then you'd have scored pretty well as almost all what you wrote was pertinent; however it was too sketchy for 30 minutes work so you do need more flesh on the bones.

[jbrownhill]

Thanks for the feedback. I do agree I need to start expanding on the points I make a lot more. With regards to the signal in question 6, it does look to me that the signal is noticeably within the lenght of the platform when compared to the starters at the other end. I took this as a hint that this is where some of the marks were to be awarded. Otherwise, why not just draw it after the end of the platform?

[PJW]

Thanks for the feedback. I do agree I need to start expanding on the points I make a lot more. With regards to the signal in question 6, it does look to me that the signal is noticeably within the length of the platform when compared to the starters at the other end. I took this as a hint that this is where some of the marks were to be awarded. Otherwise, why not just draw it after the end of the platform?

Personally I think they have effectively done this, leaving enough space to prevent the diagram being too cluttered, although I agrree that they could have shown sightly better and I'd have been tempted to put the signal more clearly at platform end, even if that meant showing the points a little further away

My interpretation of the diagram is that it depicts points 5 positioned as close to the platform end as possible. The points certainly have to be beyond the platform as else it would be foul of trains routed into the siding. My assumption would be that, to maximise usable platform length (it looks very much the same length as the turnback siding and, by implication, the fixed formation train I am assuming is used), the signal would be as close as practicable - say 2m from switch tips to block joint and another 3m to the signal, certainly I don't see this total length to be as much as 10m. However such a portion of platform beyond this signal is pretty much useless, as do need to be able to get a whole length of train in when it is at danger- therefore I believe that it could only be as a nice-to-have in order to position the train more conveniently for passenger exit, it has little benefit operationally.

I am not saying your interpretation is definitely wrong; only that I judge differently, as per rationale above. Provided that you state your assumption and it is reasonable, then I am sure examiner wuld mark answer on the basis of that assumption.

[Hort]

Hi

I attempted this question. I felt my answer to i) had a bit of repetition since i could not think of many risks!

[Peter]

Hi

I attempted this question. I felt my answer to i) had a bit of repetition since i could not think of many risks!

I remember this one being discussed at the exam review for the year in question, but I cannot find the notes from that meeting to see if there were any examiners comments published on that discussion. I do however recall that, consistent with your difficultly in listing items, the room was quite quiet when the discussion was started, so you are not alone!

You have majored on that fact that, given the described service pattern, most of the SPAD risk is with SAS SPADs because all trains are planning to stop there anyway. The question does not say one way or another whether this is the case and I think that you were therefore correct to put the bits about reading time and braking in section 2 because that is asking for things that are not apparent from the service pattern description.

One item that I think probably would better be included in part 1 is about the visibility of the signal at the normal stopping position (ie can the driver see it properly). You talked about it part 2 so you would probably get credit for it even if the examiner thinks it is in the wrong place - they are usually OK like that.

I think that you would have got reasonable marks on this, but not outstanding. You got the balance of amount of writing correct - the second was probably looking for less than half that of the first. Depending on how much detail that you put into the points from item 1, given the 18 marks, one would expect there to be 6 (3 marks each in a lot of detail) or 9 (two marks each with less detail). Assuming that all of the items are relevant, I think the way the examiner was talking at the review, you would have got somewhere near half the available marks. That said, I was struggling to come up with more items to add to the discussion.

One minor point. You mentioned AWS at one point. I'm no metro expert and hence not sure whether any metros use AWS in the form that the main line people would know about. Perhaps more consideration of ATP setup would be useful here.

Peter