2012 Module 2 Layout Attempt

[PJW]

Hi all,

PFA for 2012 module 2 layout attempt and calculation.

Please provide your valuable comments for future improvement.

Thanks in advance.

Prabhakar

Firstly apologies for the length of time taken to look at this;  a period of leave and then a particularly challenging time both at work and domestically has coincided with a flood of last minute interest in exam preparation by quite a few, some contacting via this Forum and others by diverse means and overwhelmed.  Moral students need to start earlier next year!

However looking at calcs, these are good but could be better explained; conversely some of what you spent time on wasn't of great value.  

1. Diagram to explain the derivation of headway formulae more essential than your graph of "braking characteristic" which I don't think adds anythingb and not quite sure what it means anyway

2. worth explaining the conversion factor to m/s; you have just injected 5/18 factors without explaining on first use.

3. Headway calcs are for 120km/h; therefore the freight which only goes at 100km/h cannot be relevant; there is only one of them an hour anyway!

4. Explanation of why you decided upon headway requirement of 225 secs on page 3 was GOOD

5. Further down in explanation re 3 or 4 aspect signalling, generally ok, but should have made clear that 4 aspects can be almost double the price (based on increased number of signals and more separate train detection sections needed per unit length of railway) and so strong incentive only to use 4 aspects when there is tangible benefit of so doing; I don't disagree with overall conclusion though.

6. Treatment of the branch was GOOD, particularly the diagram
You did waste some time because a bit repetitive (figures could have ben reused from page 1; iyt took you some time to realise that the branch had two identical sections and that "ditto" was appropriate.
However you didn't calculate EXACTLY what was needed; you decided that the re-entry time was 922 sec when that was really the time between one train going onto the branch and then getting off again.  You should have added a time (say 40sec) to allow for the point to be freed up after the back of the train has passed clear, then signaller realise, then set a route for train2 onto the branch, the points to move, the signal to clear, the driver to notice, close the train doors, take off the brakes and then apply power and get to the branch points.
Issue is that there is a bare minimum of 16 mins between trains and that for timetabling purposes it could at most sustain 3 trains per hour.  Since in fact there are 2 passenger trains an hour (it does not say but the implication is that it is a half hourly "clockface" service) and a freight also to fit in to the pattern (of course goes beyond B to A and therefore "goes" but does not "come back" or vice versa in any one gap in the passenger service, it could probably just about work as a single block section from E to B.  However may well be worth splitting that into two; in which case the obvious place to put intermediate signals is at station C in both directions of travel.

7. On the last page (which could have done with a heading relating to the rationale for the signalling that you actually intend to use for signallling the layout), it was hood that you clearly presented the minimum and maximum spacing for 3 and 4 aspects (since you have already stated you will deploy 4 aspects in a specific area and 3 aspects elsewhere), but you should have explained where the 1.5 factor came from.  You have just said "assuming 50% margin" when in fact the maximum spacing permitted is based on what it is reasonable amount by which sections may be overbraked before the risk of driver complacency leading to SPAD when a shorter section elsewhere is encountered is assessed as being too high.  You should also have justified that the maximum spacing (in the case of 3 aspects) would actually satisfy the headway constraint as well.
The last paragraph relates to the branch, but as we have stated above few section signals are needed and so the minimum will relate to the braking between the Y/G and the section (R/G) signal and the headway constraint (don't actually need to consider since have effectively already covered in discussion (section 6 above) relates to the separation of the section signals.  Your presentation seems to suggest that you may not have fully comprehended and have just multiplied the min braking distance value by 1.5.

Overall though the calcs were well laid out, clearly legible and understandable; not a bad attempt but attention to the items above would make them even better.