Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
2008 Module 2 Layout Calculation Attempt
#1
I have read that some one have made a calculation of 2008 Module 2 before, but some small errors in it, and he did not calculate headway and signal spacing for stopping trains. I attempt this calculation again, hope for your feedback!
My work is taking the attached powpoint as an example. It is my 1st work~


Attached Files
.pdf   page3.pdf (Size: 78.41 KB / Downloads: 281)
.pdf   page2.pdf (Size: 63.25 KB / Downloads: 248)
.pdf   page1.pdf (Size: 92.22 KB / Downloads: 341)
.pdf   page4.pdf (Size: 63.06 KB / Downloads: 184)
.pdf   page5.pdf (Size: 72.53 KB / Downloads: 186)
Reply
#2
(16-04-2010, 11:42 AM)greensky52 Wrote: I have read that some one have made a calculation of 2008 Module 2 before, but some small errors in it, and he did not calculate headway and signal spacing for stopping trains. I attempt this calculation again, hope for your feedback!
My work is taking the attached powpoint as an example. It is my 1st work~

For first attempt it is quite good. Certainly neat and easy to read with good diagrams. Well laid out overall.
BUT you didn't explain enough, logically messy, some dodgy parts and some bits assembled in the wrong order to impress the examiner.
I think it shows that you have studied a range of relevant material and can reproduce it but perhaps you have not yet completley understood and therefore how to fit it together into a cohesive whole.

So looking at your answer
1. Explain the conversion from km/h into m/s

2. Explain how you calculated braking distance [it is at very foot of page but should be shown the first time you use it].

3. You quoted formula for headway distance without explanation or even defining the terms used within it, You had a very good diagram on page 2 which would have been better placed here to help explain it, but you also should have marked the headway distance an (assuming you are going to use it) the distance Green to Red as well as explaining "S" (the diagram effectively does the other terms).

4.For clarity you should have said that the values you obtained for 3-aspect and 4-aspect were the "best achievable" for that form of signalling with signals placed at minimum spacing.

5. Having done these calcs then you didn't need to do the bit at the bottom of page 1 re Green to Red distance. All you needed to do was to calculate was what headway was actually needed by the train service / specified requirements and then compare to to those values calculated for the two forms of signalling. In your calc you just presented the value of 1205 without explaininng its derivation.

6. If you do wish to use distance Gren to Red instead then you do need to explain. Don't just say that 1.5<N<2 means 4-aspects; justify by explaining the significance.

7. Also you initially said D4 = 0,5BD but later that D4=1307m which is not. You must be careful to distinguish between the "best possible" headway when signals are at minimum spacing, and the "headway" that results from signals are at a certain greater spacing. I think what you were trying (quite correctly) to do was establish what was the maximum spacing that would just provide the headway you were aiming for.

8. Page 3 starts well, but beware that this calculation of the additional time taken compared with a non-stop train is not taking any account of how a driver would drive their train given the aspects that they would encounter.

9. However it then seems as you don't really understand. There was no sense in calculating what the headway would be for 3-aspects; you have already rejected this option as it is not capable of delivering the non-stop requirement. Also you based your 4-aspect value on the "best possible" headway from page 1 rather than the headway relevant to the spacing you chose on page 2.

10. As a free standing diagram, page 4 was fine, but didn't seem to tie in well with the rest. You should have explained what you were using it to calculate and why. You should also have commented whether a train starting from rest at a station really needs to see a Green; in 3-aspect signalling then the answer is yes but in 4-aspect signal a Double Yellow is generally regarded as good enough to persuade the driver to accelerate as hard and for as long.

11. Continuing onto page 5, you try to calculate headway time- BUT you can't use that equation since the train is accelerating and therefore V is not a constant. To calculate t2 you need to know how much of the distance (3D+O+L) is left and therefore you must calculate distance d1 first.
Somehow you tried to get a value of t2 and d2 first!

12. So as an examiner I am left confused what value you are going to use for your signal spacing because on page 2 you seem to say 1307m whereas on pade 5 you seem to say 1966m and you don't have any summary to bring things together.

So as I said initially you seem to have got all the right bits and most of the separate elements are fine, but you don't completely convince me that you understand.

Pay a bit more attention to explanation, what values are minima, which are maxima. You are certainly on the right lines, but not quite there yet- not a bad first attempt though
PJW
Reply
#3
Quote:Dear Sir,
I have attempted 2004 mod-2 paper as per indian practice & to my knowledge. Kindly have a look at it & tell me what improvements can i make. I also tried to attach it at IRSEEXAM site but was unable to attach because of the attachment prompt does not open. Waiting for your reply.

Amit Kumar Srivastava

I think it was a high resolution scan and therefore over the 1 MB file size limit. I have printed, commented on it and rescanned and attach here as a pdf

It was extremely good presentation in many ways; however I am afraid that you didn't actually read the question carefully enough as it was a bit different in 2008 than in other years.

a) Determine minimum braking distances for the permissible speeds and braking characteristics of the traffic on offer.
b) Determine graphically, or by calculation, the headway at minimum signal spacing and the
given speed for:
i) A fast passenger train following another fast passenger train; AND
ii) A fast passenger train following a stopping passenger train.
All calculations and graphs must be shown [20 Marks]


For part a) you only calculated for one type of traffic- passenger on the mainline.
You reproduced extremely well an explanation of how to determine the best form of signalling for the layout- but they didn't actually ask for that!

In part b) ii) (that you did first rather confusingly) again you gave a very good presentation but this was for a STOPPING train following another STOPPING train- this was not that which was asked.

In part b) i) you calculated non stopping headway for 4 aspects spaced at 1100m. The question asked for the headway at minimum spacing which is surely the braking distance- there is no hint that you should have utilised 4 aspects. This comment also applies to b) i)

When I first looked at your answer it was without having read the question paper and I then thought it was extremely good. However then I looked at the question paper.
Although you would certainly pick up a lot of marks, you'd also lose a lot for having answered the questions you wanted to answer, not the ones that the exam had set.

As always READ THE QUESTION
DON'T ASSUME


Attached Files
.pdf   2008 calcs.pdf (Size: 354.68 KB / Downloads: 278)
PJW
Reply
#4
In part b2, why do you think it means 3 aspect at 2010m spacing?
According to the calculation, 3 aspect can not fit for the requirement. Min signal spacing means the distance between any two signals, or between Red and Green signal? If take 4 aspect and signal spacing as 0.5*BD, isn't it the min spacing?

Reply
#5
(16-09-2010, 09:26 AM)greensky52 Wrote: In part b2, why do you think it means 3 aspect at 2010m spacing?
According to the calculation, 3 aspect can not fit for the requirement. Min signal spacing means the distance between any two signals, or between Red and Green signal? If take 4 aspect and signal spacing as 0.5*BD, isn't it the min spacing?

I agree that 3 aspects would not meet the headway requirement specified on the notes of the layout. It depends if you read the question paper itself literally. I think that you could perhaps make a case for interpreting "at minimum spacing" to be "at minimum spacing that not only respects the braking but also the headway requirement" but you did not state that as an assumption.
The wording of the question referred to the categories of traffic and speed but certainly did not mention capacity / headway and therefore I read into the wording is that this was deliberately not to be included within the consideration.

The fact that other bits of your answer seemed to be following the pattern of an approach which was suitable to other years rather than what was requested on this occasion, adds to the view that the examiner is likely to form. That is why you need to be very careful to state your interpretation when a question seems a bit ambiguous- apart from anythhing else it demonstrates that you have read carefully and are trying to answer
PJW
Reply
#6
Then even if 3 aspect is avaliable in some layout, but signal spacing of 4 aspect is 0.5*B.D, which must be smaller than 3aspect--B.D. So if the question asked like this one, we should choose 4 aspect to calculate headway?

(16-09-2010, 06:01 PM)PJW Wrote:
(16-09-2010, 09:26 AM)greensky52 Wrote: In part b2, why do you think it means 3 aspect at 2010m spacing?
According to the calculation, 3 aspect can not fit for the requirement. Min signal spacing means the distance between any two signals, or between Red and Green signal? If take 4 aspect and signal spacing as 0.5*BD, isn't it the min spacing?

I agree that 3 aspects would not meet the headway requirement specified on the notes of the layout. It depends if you read the question paper itself literally. I think that you could perhaps make a case for interpreting "at minimum spacing" to be "at minimum spacing that not only respects the braking but also the headway requirement" but you did not state that as an assumption.
The wording of the question referred to the categories of traffic and speed but certainly did not mention capacity / headway and therefore I read into the wording is that this was deliberately not to be included within the consideration.

The fact that other bits of your answer seemed to be following the pattern of an approach which was suitable to other years rather than what was requested on this occasion, adds to the view that the examiner is likely to form. That is why you need to be very careful to state your interpretation when a question seems a bit ambiguous- apart from anythhing else it demonstrates that you have read carefully and are trying to answer

Reply
#7
(19-09-2010, 08:11 AM)greensky52 Wrote: Then even if 3 aspect is avaliable in some layout, but signal spacing of 4 aspect is 0.5*B.D, which must be smaller than 3aspect--B.D. So if the question asked like this one, we should choose 4 aspect to calculate headway?

I obviously do not know what the examiners would expect; all I can say is what I would do if a candidate.

My logic is that
part a) says: Determine minimum braking distances for the permissible speeds and braking characteristics of the traffic on offer.
Therefore I would do that for the various speeds / braking rates mentioned.
part b) then says: b) Determine graphically, or by calculation, the headway at minimum signal spacing and the given speed for........
Since this makes no reference to the layout and its headway requirements but only asks what the headway would be at minimum signal spacing, it seems logical to me that 3 aspects are assumed . Potentially could cover yourself by also calculating for 4 aspects spaced at 0.5 BD- I suppose it would not take long to do so and therefore probably worth it. Of course, in the exam always have to decide whether any time spent would be better employed doing smething different that may get more marks per minute......

PJW
Reply
#8
Oh, I see... Thanks......

(19-09-2010, 08:24 AM)PJW Wrote:
(19-09-2010, 08:11 AM)greensky52 Wrote: Then even if 3 aspect is avaliable in some layout, but signal spacing of 4 aspect is 0.5*B.D, which must be smaller than 3aspect--B.D. So if the question asked like this one, we should choose 4 aspect to calculate headway?

I obviously do not know what the examiners would expect; all I can say is what I would do if a candidate.

My logic is that
part a) says: Determine minimum braking distances for the permissible speeds and braking characteristics of the traffic on offer.
Therefore I would do that for the various speeds / braking rates mentioned.
part b) then says: b) Determine graphically, or by calculation, the headway at minimum signal spacing and the given speed for........
Since this makes no reference to the layout and its headway requirements but only asks what the headway would be at minimum signal spacing, it seems logical to me that 3 aspects are assumed . Potentially could cover yourself by also calculating for 4 aspects spaced at 0.5 BD- I suppose it would not take long to do so and therefore probably worth it. Of course, in the exam always have to decide whether any time spent would be better employed doing smething different that may get more marks per minute......

Reply
#9
I am inviting guidance and correction on the attached attempt on the calculations part of the 2008 paper; especially with a view to make it achievable within 18 minutes for a novice practising to finish the paper in 90 minutes.


Attached Files
.jpg   2008 CALCS 001.jpg (Size: 538.65 KB / Downloads: 200)
Reply
#10
It seems a very reasonable attempt. I've not checked the maths but I do have a couple of comments.

1) equations need to be derived and show what each of the symbols mean.
2) assumptions need to be stated.
3) explination of what is being written is always helpful.

Else, well done.
Jerry

Le coureur
Reply


Forum Jump:


Users browsing this thread: 1 Guest(s)