I think that most of it is very good.
A few quibbles:
a) I think that 1000/(60 x 60) is a clearer way of showing the conversion of km/h imto m/s than 5/18
b) Having decided to round up the speed to 2 significant figures, you shouldn't quote to the precision you have when you square to get the distance.
Must admit that I think question wording is poor regarding whether need to show best headway for both 3 aspects and 4 aspects. One could say the best implies 4 aspects, hence don't worry re wasting time on 3 aspects; alternatively one could read it as signals at braking distance and therefore it is the 4-aspects calculation which is not needed. Therefore I think like you I'd have done both to be sure.
You didn't quite do the stopping headway bit, although most of what you did was ok and going in the correct direction. The issues that I have with it:
1. You have assumed that driver does not brake at all when passing the signal prior to the station but continues at headway speed until last possible moment to brake to a stand. This would not be how a driver would be expected to drive in the UK if that signal had been showing a cautionary aspect. It is not clear from your explanation what aspect you are expecting that driver to have received.
2. What you have actually calculated is the TOTAL time for a stopping train to travel the distance of two signal sections (188.2 sec). You then add this to the non-stop headway time without any explanation relating to how this gives the result you were asked for; you are supposed to be calculating the timetabled allowance between train 1 and train 2 when leaving their origin such that after train 1 has stopped and train 2 has not that they are then at minimum headway. I think you have nearly done what was needed, but not quite.
3. You have done the maths purely on the basis of decelerating and accelerating of trains, yet really have not related this to signalling at all. We need to be sure that the signalling we provide does not prevent the trains being driven in such a manner that the required headway can be achieved; your aswer does not address this element as far as I can see.
4. You haven't done much to explain how the results determines your choice of signalling; perhaps you intend to do that determination next, but don't forget to explain it to the examiner- it is part of the question so I guess there may be some 4 or 5 marks reserved for it.
Overall thought was neat, clear, well presented, suitable level of detail so a very respectable effort. It is the stopping calcs which demand more attention; see also my comments on a recent attempt at 2011 in which the same fundamental question is being addressed.
A few quibbles:
a) I think that 1000/(60 x 60) is a clearer way of showing the conversion of km/h imto m/s than 5/18
b) Having decided to round up the speed to 2 significant figures, you shouldn't quote to the precision you have when you square to get the distance.
Must admit that I think question wording is poor regarding whether need to show best headway for both 3 aspects and 4 aspects. One could say the best implies 4 aspects, hence don't worry re wasting time on 3 aspects; alternatively one could read it as signals at braking distance and therefore it is the 4-aspects calculation which is not needed. Therefore I think like you I'd have done both to be sure.
You didn't quite do the stopping headway bit, although most of what you did was ok and going in the correct direction. The issues that I have with it:
1. You have assumed that driver does not brake at all when passing the signal prior to the station but continues at headway speed until last possible moment to brake to a stand. This would not be how a driver would be expected to drive in the UK if that signal had been showing a cautionary aspect. It is not clear from your explanation what aspect you are expecting that driver to have received.
2. What you have actually calculated is the TOTAL time for a stopping train to travel the distance of two signal sections (188.2 sec). You then add this to the non-stop headway time without any explanation relating to how this gives the result you were asked for; you are supposed to be calculating the timetabled allowance between train 1 and train 2 when leaving their origin such that after train 1 has stopped and train 2 has not that they are then at minimum headway. I think you have nearly done what was needed, but not quite.
3. You have done the maths purely on the basis of decelerating and accelerating of trains, yet really have not related this to signalling at all. We need to be sure that the signalling we provide does not prevent the trains being driven in such a manner that the required headway can be achieved; your aswer does not address this element as far as I can see.
4. You haven't done much to explain how the results determines your choice of signalling; perhaps you intend to do that determination next, but don't forget to explain it to the examiner- it is part of the question so I guess there may be some 4 or 5 marks reserved for it.
Overall thought was neat, clear, well presented, suitable level of detail so a very respectable effort. It is the stopping calcs which demand more attention; see also my comments on a recent attempt at 2011 in which the same fundamental question is being addressed.
(09-03-2012, 11:56 AM)vedprakash Wrote: Hi
I did calculation for 2010 layout but I lost the plot somewhere, please have a look and bail me out.
Ved
PJW