25-09-2012, 09:27 PM
Overall these were quite good, certainly easy to read and easy to follow- however I think that they would have taken you far too long to do within exam conditions, so do need to abbreviate somewhat. Certainly some of what you included was never actually utilised- you do not need the braking distance for the speed limit over the turnouts for example.
Having determined the maximum spacing of signals that will give required headway, you should round DOWN not up!
Using your numbers I still don't quite agree re the "DGR figure", but that is minor. More important is to emphasise that this approach is not very popular with the examiners and if you utilise you MUST make it clear that you know the relevance of N=2. You have drawn diagram but you should have stated that unless can fit two min braking distances within the max headway distance that 3 aspect signals cannot meet the capacity requirements.
The question asked for:
a)Determine the minimum braking distances for the permissible speeds and braking characteristics of the traffic specified on layout 1.
b) Determine graphically or by calculation the theoretical best headway (without any allowances) at minimum signal spacing and the given speed
By this point you had already done a) or rather you had for the 160km/h but not for the 100km/h as far as I could see; it would have been good for you to have dawn attention to these figures in your answer.
I then got a little confused whether you were attempting to consider, having ruled out 3 aspects, the next most economical approach (i.e. 4 aspects spaced at 150% BD, note not BD+150%) or instead 4 aspects at minimum spacing. As I read the words of the question you did need to do the latter which in fact you did at the bottom of page 4. The info above this was actually relevant to the solution you need to adopt on your layout so was not superfluous but it would have helped had you been clearer when you were doing the exercise requested by the question paper and when you were justifying the solution to be used when actually placing signals on the layout. This presentation could also have been clearer that you were determining which of the maximum (i.e. capacity / overbraking) was the more onerous; again when you calculate the maximum do ensure you round DOWN rather than up.
For the stopping headway, it would have been better to have drawn your diagram on page 8 instead of the one on page 5. Also did not need to define all the symbols in Newton's equations of motion a second time around- you can't spare the time!
All was going well, if somewhat labouriously, until half way down page 6 where you compare the stopping train travelling 3084m with a non-stop train that you seem to claim covers 3716m (which happens to be the headway distance) in the same time. I rather lost you after that.
I also quibble with your last diagram as I can't rationalise the gradient of the crve with some of the annotations and also you seem to have marked some distances vertically although this is the time axis.
However overall you did show reasonable proficiency with the majority of the calculations and came up with a sensible range for placing the signals on the mainline. Given how close the exam now is I wouldn't worry about the finer points of the stopping calculations; better to spend the effort slimming down and speeding up your presentation and learning from some of the minor items above.
Similarly you need to leave yourself enough time to score the easy marks in all categories when doing the layout so I suggest that just showing how you'd start off the stopping calcs but then cutting your losses and moving on may well be a good policy.
Having determined the maximum spacing of signals that will give required headway, you should round DOWN not up!
Using your numbers I still don't quite agree re the "DGR figure", but that is minor. More important is to emphasise that this approach is not very popular with the examiners and if you utilise you MUST make it clear that you know the relevance of N=2. You have drawn diagram but you should have stated that unless can fit two min braking distances within the max headway distance that 3 aspect signals cannot meet the capacity requirements.
The question asked for:
a)Determine the minimum braking distances for the permissible speeds and braking characteristics of the traffic specified on layout 1.
b) Determine graphically or by calculation the theoretical best headway (without any allowances) at minimum signal spacing and the given speed
By this point you had already done a) or rather you had for the 160km/h but not for the 100km/h as far as I could see; it would have been good for you to have dawn attention to these figures in your answer.
I then got a little confused whether you were attempting to consider, having ruled out 3 aspects, the next most economical approach (i.e. 4 aspects spaced at 150% BD, note not BD+150%) or instead 4 aspects at minimum spacing. As I read the words of the question you did need to do the latter which in fact you did at the bottom of page 4. The info above this was actually relevant to the solution you need to adopt on your layout so was not superfluous but it would have helped had you been clearer when you were doing the exercise requested by the question paper and when you were justifying the solution to be used when actually placing signals on the layout. This presentation could also have been clearer that you were determining which of the maximum (i.e. capacity / overbraking) was the more onerous; again when you calculate the maximum do ensure you round DOWN rather than up.
For the stopping headway, it would have been better to have drawn your diagram on page 8 instead of the one on page 5. Also did not need to define all the symbols in Newton's equations of motion a second time around- you can't spare the time!
All was going well, if somewhat labouriously, until half way down page 6 where you compare the stopping train travelling 3084m with a non-stop train that you seem to claim covers 3716m (which happens to be the headway distance) in the same time. I rather lost you after that.
I also quibble with your last diagram as I can't rationalise the gradient of the crve with some of the annotations and also you seem to have marked some distances vertically although this is the time axis.
However overall you did show reasonable proficiency with the majority of the calculations and came up with a sensible range for placing the signals on the mainline. Given how close the exam now is I wouldn't worry about the finer points of the stopping calculations; better to spend the effort slimming down and speeding up your presentation and learning from some of the minor items above.
Similarly you need to leave yourself enough time to score the easy marks in all categories when doing the layout so I suggest that just showing how you'd start off the stopping calcs but then cutting your losses and moving on may well be a good policy.
(24-09-2012, 08:49 AM)Nagasri.Jonna Wrote: Hi PJW,
we are attaching calculations for 2011 mod2 layout. please find and comment on the same.
Regards,
Nagasri.J
PJW