another try at double line layout

[onestrangeday]

Hi PJW:

Thanks for taking time to review my work. I have learnt much from the comment you gave, and I think I need to think about it again.
My reply to your comments as below:

1. I have shifted the signal 13 further apart from the points area, as to make sure that the overlap distance does not included the points I think this shall be the best choices.

2. I agree, so I have moved the signal 12 into the Not Scale potions as to make sure it will not interfere other train movements over the junction.

3. I agree with you, it is not always profitable to implement bi-directional signalling system on the railway network, it’s definitely cost much. So I changed to only using one direction signalling system for station A& B, but bi-directional signalling system for station C as to allows reversal and running around movement of passenger train and freight trains.

4. I agree with you I have re-number the signal on the layout as to leave spare signals for future usage.

5. I am not sure whether my braking distance calculation is suitable or not. As stated from the question that the permitted Passenger speeds is 160km/h. (I’ve taken this figure as my braking distance calculation taking the worst case scenario into calculation), and the braking distance calculated from this is approximately 2km as shown from my calculation. However, the question also says that the required headway for following stopping trains at 120km/h is 6 min, and the non-stopping trains at 120km/h are 3 min. Or shall I taken 120km/h for the braking distance calculation and as the minimum signal spacing?

And when it comes to place signals at station area, we do not place signals 2km apart right? (As for station B there would not have such space available and for station C the station area is less than 2km (from 17.800 km~ 18.450). So I believe the signals in the station area are sometimes not be able to be placed for full service braking distance apart (home & starting signals).

So how should we place the signals at terminal as to suit headway requirement?
Sorry to ask some silly questions as above.

But as I have learnt in the past, when it comes to place signals at terminal. General speaking, we should place home and starting signals at terminals (for entering and leaving the platform area) and they shall be as close as possible to allow quick clearing of signals once train have left the terminal area. Also place junction signals before points area and make sure it’s overlap will not prevent the operation of point area as for the best choice. (But this may be always be possible due to civil constraints etc.)

If took 120km/h for calculation, the braking distance is approximately 1200m.

6. Sure, I have re-signaled the layout for reversal of passenger trains and running round of freight trains. Can you check whether it is appropriate?

I will read through other thread about how to calculate the signal spacing for a stopping train at station area for Question 4, if I have further questions I will ask again.


Attached layout is the revised version.



Thank you for taking time to correct my work

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.

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