1997 aspect sequence

[interesting_signal]

I have attempted the 1997 paper. There's a model answer in the study pack for the Up direction, but not the Down, so I'm submitting my attempt (copy of the layout also attached). I'd appreciate any comments on the transitions as I'm a bit unsure of these. Thanks in advance.

[Zaphod]

I have a couple of comments on your answer:

You seem to have neglected the call-on route from signal 107.

I don't think the 'branch' routes from signal 111 are represented correctly. For instance, when 111 is at red, 107 would be at yellow and there would be no need for BG or BH to be occupied, as you have shown. BG or BH occ is only required for the approach release of 111 to show Y+pos1 or G+pos1 so should be indicated as a condition for these, as you have with "BD occ" on 107.

I would suggest that this condition is also relevant when the warning route has been set from 107.

[PJW]

I have a couple of comments on your answer:

You seem to have neglected the call-on route from signal 107.

Whereeas I am aware that some modern aspect sequence charts do show PL aspects, this isn't traditionally required. To me (and the IRSE examiners have also regularly stated) these are not required. However a statement on the diagram that these are deliberately omitted would be wise.

I don't think the 'branch' routes from signal 111 are represented correctly. For instance, when 111 is at red, 107 would be at yellow and there would be no need for BG or BH to be occupied, as you have shown. BG or BH occ is only required for the approach release of 111 to show Y+pos1 or G+pos1 so should be indicated as a condition for these, as you have with "BD occ" on 107.

The problem to me is really how the approach release has been represented. I feel that it is actually best to show the most restrictive aspect of each signal at the bottom so that the "better aspects" are above and thus the approach release is represented by a vertical line rising to the Y / YY / G etc. This is not 100% necessary (presentations vary) but makes most logical sense to me. The important thing as Zaphod has pointed out that the "default" aspect of 111 should be shown as R and therefore joined by a horizontal line to 107 at Y. The "BG or BH occ" should be written adjacent to the vertical line as the "trip condition" which initiates the change to the Y or G- you have seemed to have applied the comment to the horizontal line that relates to all aspects, so it rather begs the question what aspect 107 would display when that condition isn't satisfied!

You depicted the aspect sequence up yto the ROL beyond 111 correctly, but I'd certainly prefer the transition initiated by BD occupied as a vertical line; it is a form of (more restrictive than usual) approach release. I think it is good practice to differentiate these "step changes" from general sequence (indeed a dotted line can be useful) although in these days of CAD diagrams everyone seems to produce angular presentations that actually I find hard to assimilate at a glance which is surely one of the main reasons fro an aspect sequence chart in the first place. Since you have followed the practice of diagonal lines for "G reading up yo YY or G" then it rather detracts by using the diagonal line here for the (W) approach release.

I would suggest that this condition is also relevant when the warning route has been set from 107.

In general a (W) route will only give a Y up to a R with ROL. However it is possible that after signal 107 has cleared then 111 is set and clear to some higher aspect. With CBI 107 would then be permitted to display the appropriate aspect as determined by that displayed by 111, although with RRI this may not always be the case and it might remain displaying Y whatever the aspect ahead. I don't see that there is any need to show this on an aspect sequence chart- we don't mention classes of routes, just aspects.

I have made some amendments to the diagram and attach here, without however redrawing to place the R consistently at the bottom as is my preference as stated.

Also see another attempt which does follow this approach and is generally a good example of neat and clear presentation.
However
a) it rather leaves the question of YY at 107 undefined and
b) by suggesting that there is braking distance between 113 and 115 (perhaps 915m is enough but if so why is the spacing of the other 4 aspect signal on the plan that which is shown?) then makes one wonder why 111 is shown as displaying YY to 115 at R.

[interesting_signal]

Thanks for the comments. Yes, I messed up the approach release on 111 because of where I had shown the R aspect. I'll take on board the suggestion to put the R at the bottom and less restrictive aspects at the top for future attempts. (I had put the red on top, in keeping with the notes in the study pack).

I had deliberately not shown the call-on route, but will add a note next time to clarify. However, referring to the 2010 exam paper, question 10, it says 'Draw an aspect sequence chart for all signals, routes, and classes of routes shown'. In this case, I would expect to have to show the PL aspects. Do you agree?

[PJW]

Thanks for the comments. Yes, I messed up the approach release on 111 because of where I had shown the R aspect. I'll take on board the suggestion to put the R at the bottom and less restrictive aspects at the top for future attempts. (I had put the red on top, in keeping with the notes in the study pack).

There are different standards all of which are acceptable; I have mentioned my personal preferences where I believe that I have a rational reason for adopting them in order to try to be helpful. It is perfectly possible to put the red on top and show the approach release downwards, or as I have done to do the minimum alteration to your diagram, to put aspects in the order R/G/Y- but you can see that this is a little bit illogical and therefore perhaps more prone to human error- I prefer to keep things simple where I can!

I had deliberately not shown the call-on route, but will add a note next time to clarify. However, referring to the 2010 exam paper, question 10, it says 'Draw an aspect sequence chart for all signals, routes, and classes of routes shown'. In this case, I would expect to have to show the PL aspects. Do you agree?

Definitely given that wording then I would certainly say that you should show ALL signals including GPLs and EVERY route from EACH signal including call-ons and shunts. To me, the examiners intended this instruction to be unambiguous, although it is indeed unexpected given their comments in previous years re the regular aspect sequence chart question. I expect that they were deliberately testing who was actually reading the specific question asked and trying to get away from the "painting by numbers" that is often evident.

We should of course get definitive answer regarding the examiners' expectations on Thursday.

[Zaphod]

Also see another attempt which does follow this approach and is generally a good example of neat and clear presentation.
However
a) it rather leaves the question of YY at 107 undefined and
b) by suggesting that there is braking distance between 113 and 115 (perhaps 915m is enough but if so why is the spacing of the other 4 aspect signal on the plan that which is shown?) then makes one wonder why 111 is shown as displaying YY to 115 at R.

There should be no YY shown at 107 as the signal is not capable of displaying that aspect. Admittedly I would have expected to see the unused aspect head blacked out rather than just left white.