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
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
(25-08-2014, 03:34 PM)asrisaku Wrote: Hi
Another attempt with a friend review. Any review is welcome
Best regards, Arnut
PJW