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calcs for 2013
#1
Hi All,
Please could anyone provide feedback for the calculation section of the 2013 mod 2 paper.

Regards

TF


Attached Files
.pdf   Mod 2_2013_ptA.pdf (Size: 703.58 KB / Downloads: 11)
.pdf   Mod 2_2013_ptB.pdf (Size: 724.19 KB / Downloads: 6)
.pdf   Mod 2_2013_ptB cont...pdf (Size: 587.57 KB / Downloads: 6)
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#2
Afternoon TF,

The question paper for 2013 asks you to:
"Determine the minimum braking distances for the permissible speeds and braking characteristics of the traffic specified on layout 1". You've only detailed the headway braking distance.

I used a table to record all the permissible line speed braking distances using the same calculations you've applied to get the headway minimum braking. You don't necessarily have to demonstrate the working out each time for each line speed, just perhaps once so that you demonstrate the underpinning maths.

Your uniform minimum signal spacing will therefore be different for the branch and main lines and will be based on the permissible line speed braking distance rather than headway braking.

You might want to consider a simple diagram for the HT3 and HT4 calculations to show how the BSOL applies. The principles of the HT3 and HT4 calculations looks fine, however the minimum spacing should be PSR based rather than headway based.

I've attached the paper and layout for anyones reference.

Hope that helps


Attached Files
.pdf   Exam 2013 Mod 2 Paper.pdf (Size: 64.31 KB / Downloads: 2)
.pdf   Mod 2 2013 Layout.pdf (Size: 344.9 KB / Downloads: 2)
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#3
Hi there, thanks for the reply. I have calculated minimum braking, (top of page one), based on the top line speed, braking characteristics which is given as 0.5 and the laws of momentum. This was then input into headway calcs to define the minimum headway time.TFREMBrum Wrote:Afternoon TF,

The question paper for 2013 asks you to:
"Determine the minimum braking distances for the permissible speeds and braking characteristics of the traffic specified on layout 1". You've only detailed the headway braking distance.

I used a table to record all the permissible line speed braking distances using the same calculations you've applied to get the headway minimum braking. You don't necessarily have to demonstrate the working out each time for each line speed, just perhaps once so that you demonstrate the underpinning maths.

Your uniform minimum signal spacing will therefore be different for the branch and main lines and will be based on the permissible line speed braking distance rather than headway braking.

You might want to consider a simple diagram for the HT3 and HT4 calculations to show how the BSOL applies. The principles of the HT3 and HT4 calculations looks fine, however the minimum spacing should be PSR based rather than headway based.

I've attached the paper and layout for anyones reference.

Hope that helps
Reply
#4
Hi TF,

The top line speed for this layout is 160km/h for non stopping passenger trains, rather than the 140km/h for the headway speed.

Part 1A of the paper is asking you to work out the braking distances for all of the line speeds detailed on the layout, i.e:
Non stop passenger trains 160km/h
Stopping passenger trains 100km/h
Freight trains – main line and branch line 100km/h

Your principles look sound, but you need to use the minimum spacing distances based on the highest permissible line speed.

This is why a table might help as it can let you show your detail quite simply and make sure you don't miss anything out.

Once you've calculated the braking distances in question 1A, you can then use the minimum spacing to help you work out the 3 and 4 aspect headways for part 1B.
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#5
Ah yes I see what you mean now, I was working from the layout - doing all my calculations and answering the questions from the left hand column rather than looking at the paper, so I must have got drawn to that 140kmh figure in bold. A classic "read the question" properly moment. Thanks for highlighting that for me. Have you looked at part B&C, would like any opinions on that part, as a little uncertain if I have used the right methods to calculate the desired headway.TF Wrote:REMBrum
Hi TF,

The top line speed for this layout is 160km/h for non stopping passenger trains, rather than the 140km/h for the headway speed.

Part 1A of the paper is asking you to work out the braking distances for all of the line speeds detailed on the layout, i.e:
Non stop passenger trains 160km/h
Stopping passenger trains 100km/h
Freight trains – main line and branch line 100km/h

Your principles look sound, but you need to use the minimum spacing distances based on the highest permissible line speed.

This is why a table might help as it can let you show your detail quite simply and make sure you don't miss anything out.

Once you've calculated the braking distances in question 1A, you can then use the minimum spacing to help you work out the 3 and 4 aspect headways for part 1B.
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#6
I think there are probably marks for showing how you derive the 3 & 4 aspect headway formulae rather than just quoting them. It's quick enough to draw a diagram to illustrate this.
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#7
Morning,

Looking at the response to question 1C, firstly I'd say check the diagram you've given- always good to give a diagram, but the question asks you to consider a stopping service leaving the down loop (rather than the down main). I don't think this affects the calcs in this instance.

Your calculations to understand the speed to reach linespeed for the stopped service look correct. The remaining calculations for the distance to the branch protecting signal and the linespeed calculations also look good (obviously the actual answer would be slightly different due to the signal distances, but your principles are sound).

My only other comment would be that you've added a 30 second dwell time when adding the overall time for the stopping train to reach linespeed and clear the branch protecting signal overlap. You could consider driver reaction time here for the driver to notice the proceed signal (approx. 5 seconds), but I'd say there's no need to consider a full dwell time- the question paper asks you to consider the headway following the departure of the stopping service only.

Good stuff, keep going!
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#8
Thanks once again, really appreciate the comments. Its a been a bit quiet in the forum this year, and is always helpful to get some good feedback, especially this close to the exams. I Just made an assumption on dwell time, and also I did all my calcs with train leaving the down main as seemed like the easiest way to calculate the required headway. I thought about considering both train movements from their starting positions but decided it would add too much complexity for me to think about, especially under exam conditions. TF Wrote:REMBrum
Morning,

Looking at the response to question 1C, firstly I'd say check the diagram you've given- always good to give a diagram, but the question asks you to consider a stopping service leaving the down loop (rather than the down main). I don't think this affects the calcs in this instance.

Your calculations to understand the speed to reach linespeed for the stopped service look correct. The remaining calculations for the distance to the branch protecting signal and the linespeed calculations also look good (obviously the actual answer would be slightly different due to the signal distances, but your principles are sound).

My only other comment would be that you've added a 30 second dwell time when adding the overall time for the stopping train to reach linespeed and clear the branch protecting signal overlap. You could consider driver reaction time here for the driver to notice the proceed signal (approx. 5 seconds), but I'd say there's no need to consider a full dwell time- the question paper asks you to consider the headway following the departure of the stopping service only.

Good stuff, keep going!
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#9
Thanks Dorothy, not sure why I didn't include one actually, I think I have done one in all my other practice papers. Will definitely keep this in mind for the exam. TF Wrote:dorothy.pipet
I think there are probably marks for showing how you derive the 3 & 4 aspect headway formulae rather than just quoting them. It's quick enough to draw a diagram to illustrate this.
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