Layout:
1. You should also have shown the signals on the approach to 11 and 13, particularly as signal 13 is placed so close to the junction that the points must be within its locked overlap and there obviously has to be an "acceptance home" at which trains can be held awaiting the conflicting movement to pass clear of the junction.
2. Signal 12 seems to be too close to junction- ideally would want the rear of any train held at it not to trail back and prevent other train movements over the junction.
3. You have signalled both lines bidirectionally from this junction. Not wrong and the facing & trailing crossovers do suggest use of the platforms at A for turning back trains at least. In the UK bi-di signalling like this is rare, though actually with more recent thoughts and "modular signalling" will become more common. However for this exercise re headway I don't think it is needed and thinking re the exam then it would be unnecessary and consume valuable time.
4. Very sensible to leave gap in numbering system for the Not To Scale potions. However does imply only 1 "missing signal". The distance between scale portions is 4km and if providing continuous 3 aspect signalling then would require signals spaced reasonably equally, separated by at least braking distance but not too much more than that amount. There would probably be more signals (based on the other signals shown on this plan, but see item 5) and therefore should either have calculated, indicated their positions and numbered signals accordingly, or perhaps have used a separate numbering sequence at each "island" of signalling- could have used prefixes A, B, C etc. according to the station related.
5. For those signals you have shown, it looks like you are spacing at 500m - 700m yet you calculate braking distance as 2000m. Need to explain / rationalise.
If we say there is a signal 17 midway between 15 and 19 then this would be ok, but in that case 19 would not be braking distance from 23. This is possible but would need special controls Another possibility would be not to have a signal 19 but use 23 instead, if 17-23 a distance which isn't too excessive. Alternatively perhaps eliminate 23. Need to look at the calculations before determining course of action here.
6.Certainly do not need signal 36; the line is shown as uni-directional by the arrows. Also should place some signals on this end of the plan. Station C itself does need the signalling you have shown to permit the reversal of passenger trains requested; also needs some signals to permit running round of freight trains and that means getting a loc to rejoin the other end of its train and therefore a permissive movement.
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Re calculations of non-stop and stopping headways:
a) look at other threads in this section of the website http://www.irseexam.co.uk/forum-45-page-1.html
b) Look at the Appendix G of the IRSE Module 2 Study Pack on the DVD you get when registering to sit the exam. This is a much updated version of the old "IRSE Green Book" number 13.
However the "Railway Signalling" textbook you quote does indeed have details of the calculation of stopping headway from page 22 to 25 and it is the non-stopping that is covered on pages 8 - 11.
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To clarify:
MINIMUM signal spacing is set by BRAKING from HIGHEST PERMISSIBLE speed (directly in the case of 3 aspects, between ALTERNATE signals in the case of 4 aspects)
MAXIMUM signal spacing set by the more restrictive of:
a) the acceptable levels of over-braking (often 133 or 150 percent)
b) the HEADWAY requirement.
I'll look at your numbers separately.
1. You should also have shown the signals on the approach to 11 and 13, particularly as signal 13 is placed so close to the junction that the points must be within its locked overlap and there obviously has to be an "acceptance home" at which trains can be held awaiting the conflicting movement to pass clear of the junction.
2. Signal 12 seems to be too close to junction- ideally would want the rear of any train held at it not to trail back and prevent other train movements over the junction.
3. You have signalled both lines bidirectionally from this junction. Not wrong and the facing & trailing crossovers do suggest use of the platforms at A for turning back trains at least. In the UK bi-di signalling like this is rare, though actually with more recent thoughts and "modular signalling" will become more common. However for this exercise re headway I don't think it is needed and thinking re the exam then it would be unnecessary and consume valuable time.
4. Very sensible to leave gap in numbering system for the Not To Scale potions. However does imply only 1 "missing signal". The distance between scale portions is 4km and if providing continuous 3 aspect signalling then would require signals spaced reasonably equally, separated by at least braking distance but not too much more than that amount. There would probably be more signals (based on the other signals shown on this plan, but see item 5) and therefore should either have calculated, indicated their positions and numbered signals accordingly, or perhaps have used a separate numbering sequence at each "island" of signalling- could have used prefixes A, B, C etc. according to the station related.
5. For those signals you have shown, it looks like you are spacing at 500m - 700m yet you calculate braking distance as 2000m. Need to explain / rationalise.
If we say there is a signal 17 midway between 15 and 19 then this would be ok, but in that case 19 would not be braking distance from 23. This is possible but would need special controls Another possibility would be not to have a signal 19 but use 23 instead, if 17-23 a distance which isn't too excessive. Alternatively perhaps eliminate 23. Need to look at the calculations before determining course of action here.
6.Certainly do not need signal 36; the line is shown as uni-directional by the arrows. Also should place some signals on this end of the plan. Station C itself does need the signalling you have shown to permit the reversal of passenger trains requested; also needs some signals to permit running round of freight trains and that means getting a loc to rejoin the other end of its train and therefore a permissive movement.
=====================================================
Re calculations of non-stop and stopping headways:
a) look at other threads in this section of the website http://www.irseexam.co.uk/forum-45-page-1.html
b) Look at the Appendix G of the IRSE Module 2 Study Pack on the DVD you get when registering to sit the exam. This is a much updated version of the old "IRSE Green Book" number 13.
However the "Railway Signalling" textbook you quote does indeed have details of the calculation of stopping headway from page 22 to 25 and it is the non-stopping that is covered on pages 8 - 11.
=====================================================
To clarify:
MINIMUM signal spacing is set by BRAKING from HIGHEST PERMISSIBLE speed (directly in the case of 3 aspects, between ALTERNATE signals in the case of 4 aspects)
MAXIMUM signal spacing set by the more restrictive of:
a) the acceptable levels of over-braking (often 133 or 150 percent)
b) the HEADWAY requirement.
I'll look at your numbers separately.
(02-11-2011, 07:02 AM)onestrangeday Wrote: Hi Signalling Professionals:
Here is another exercise attempt I have done for a double line layout I hope I am on the right track. Any comments and suggestions are highly appreciated and welcomed.
For the Question 4, can anyone provide comments on how to approach the question? I have looked though the ‘railway signalling’ textbook (page 20~27) that it has only described the method for calculating the headway for a stopping trains, but does not have description on the signal spacing for stopping trains, so I hope someone can provide any suggestions on this.
In my learning experience, I’ve learnt that the (max & min) signal spacing is determined from the type of signalling system used (using the 2,3,4 aspect formula) to see whether it meets the headway requirement defined by the customer.
Thanks
PJW