(22-09-2010, 05:12 PM)alexgoei Wrote: Sorry for the late request. Would appreciate it if you can let me have your comments.
Cheers
Alex
Valley Branch
1. Should show the previous / next signals on the Not To Scale portion of line at B
2. This might explain why 202 is 3 aspect and 201 only 2 aspect.
There was nothing in your braking /headway calculations that explictly considered this segmant of the layout. Sounds as if only 3 or 4 trains an hour, so isolated 3 aspects i.e. Y/G and R.G signals do seem appropriate. The critical portion is over the single line portion and so changing to closely spaced 3 aspcts in this area may be sensible.
202 should be an auto?
3. No idea why you think you need treadles CEQ and DEQ. Similarly the other treadles at the end of the single line. I note that CMQ is on approach to its signal whereas most are towards end of their overlap. Perhaps you are confused with OTW-NS but as I see this line is operated by TCB and don't see the need for treadles.
4. 701A. Probably a good idea to have an overrun spur here if practicable, though geographically likely to be challenge given that viaducts generally bridge deep steep sided valleys, so perhaps close to 201 may be a possibility.
Need a sentence of explanation so that it doesn't look like trap points- the risk of a head-on collision on the viaduct needs to be balanced against the risk of plunging the train into the valley when it crashes into the buffers at the end of that short spur. I suppose that TPWS ought to have applied the brakes when 201 is SPADed so that should help in either scenario. Sensible normal lie for 701
5.203 already mentioned. Arrrows should name the next signal when the distances are not the same
6. 502, 501 already mentioned in route box section. As far as possible try to avoid signals and even track circuit limits on viaducts, but yes you do sometimes need to provide.
7. 703B I suppose you provided because you thought freight train being left there unattended. Perhaps it may be possible to have a length of spur / sanddrag beyond 204 parallel to running line- worth a note on plan to investigate feasibility to lower junction risk
8. Assume the 75m is the reduced overlap for 206, jusified by the permissible speed (plan would infer 100km/h but I think you could define this portion of the branch to be slightly lower). Where there are two signals like here and the overlap symbol at CL/Ck is not clear to which it applies, you should clarify by adding 204G against the 60m just to clarify intention.
9. A pure trap point like 704 should not be shown with such a long length of line and definitely not a bufferstop at the end of it- inreality generally a legth of rail that is not even as long as a normal point, it throws the vehicle off prior to where the crossing would be at the end of the switch rail.
711B shown much better.
10. I don't think 707D helps- it throws a SPAD so that it is foul of the Up Main and the Up valley Branch rather than just the former! There is not much you can do here given the requirement to provide standage. What you haven't shown is any overlap beyond 207- you can get a safe state in the event of a running (as opposed to a start away) SPAD by locking the junction. I suggest extending the overlap to the AF/AG joint; yes it is restrictive but that is the price of achiving both the standage and junction safety.
11. Confused with your point numbering. 701A and 701B for the switch diamonds is fine. 707C and 707E should not share a number a i would preclude 707C Normal with 707E Reverse simultaneously and that is a combination that would be needed to allow a train onto the Valley Branch from the Up Main at the time there is a train passing on the Down Main.
Even 3 point ends on one number is nowadays considered high, some 4 ended points exist but never remmber as many as five. The thing that is confusing though is that it is 701A, 701B, 707C, 707D, 707E.
For simplicity I think that in a double junction I'd advise you to number the switch diamond as you have and then make both 707C and 707E individual point numbers.
Main Lines
1. Again depiction of signals in the NTS area at A would help explain the itention; there are 4 aspects on the Down and 3 aspects on the Up. Presumably athe 4 aspects are just through the station and therefore transition from 3 aspects sould be shown / alluded to.
2. Comments in station area mainly in the route box feedback. The overlap beyond 105 would be foul; it should be no further to the right than the switch diamonds and therefore either be reduced or preferably signal 105 moved slightly further away from junction.
3. 110 / 112 would not display flashing yellows; the divergence speed at 707E is too low and 108 would be MAR.
4. You are right to recognise that there are few trains wrong road along th Down main, so the non red 110 signal appropriate; it would have been better placed opposite 112 even if that makes it overbraked. As it is, most certainly overbraked given how far it is placed from its red. I wouldn't have it there at all but much closer to 106.
You would need to work out where it would naturally fall from braking considerations; I'd be hoping that I could place it opposite 110 instead. The permissible speed of the line in that direction is not explicitly stated and it would not be appropriate to assume 140 kmh as the track is unliely to be designed and maintained equally for this direction of travel. Don't forget that the train is mainly operating on the branches at a maximum speed of 100kmh so unlikely to want to exceed that. In addition the train will need to stop at station C and traverse the 40kmh pointwork. Hence I'd work out that speed would mean that a distant opposite 110 would give enough distance, consider if this seemed to be a sensible speed for the line in that direction (considering the attainable having accelrated from junction D and needing to brake for station C) and the state that speed as an assumption.
5. You have transitioned to 3 aspect signals on the Down main beyond junction D which seems sensible; a comment from last time applies re 113 needing to look as if it is a 4 aspect since its yellow relates to half braking distance.
You should also have shown how the 4 aspect signalling on the Up was to transition from the 3 aspects which I assume would be further to the right on both running lines. However I am a bit confused because your calculations seemed to assume 4 aspects throughout, so in which case why did you show various 3 aspects as if you were intending to transition?
Lake Branch
1. Since it is a passenger branch, you don't need trap points 712B
2. I note FGQ treadle but am unclear why you have provided. You do need to give an explanation.
3. You made a decent attempt at the AOCL. Nowadays we'd not out new ones in I think, but have an ABCL instead- these are effectively just the same with the addition of barriers. Perhaps I'll look at your maths searately re positioning of the signs etc. but you have certainly got the idea. The concept of operation does rely on the rail driver hving a good enough view of the crossing and DCI from the SSRB and this may be a challenge as drawn in the Down direction- I expect that the crossing speed may actually need to be quite a bit lower in order to comply but the principle is there.
Given the number of treadles that you have about the layout, you should have put some here. They can be used for strike in and also for proving that the train has passed over the crossing; indeed on a single or bi-directional line they are used in conjunction with the crossing track to determine the direction of the movement being made over the crossing.
4. The main problem with the branch is that it appears to be fully signalled in the Down direction but just rely on verbal authorisation on the return journey. Obviously this does not impose any opposing route locking.
Given that you have decided to fully track circuit, then you should have stuck with Track Circuit Block and provided a red/ green platform starring signal. Given the length of the line then this is not too excessive signalling in this case. You do seem to have more track circuit joints than you need; why have FJ/FL or FM/FN or FP/FQ?
Suggest that you should have used axle counters on this line; nowadays a multi-section ACE with heads at each of the retained track joints would have been sufficient but the alternative would have been to have provided fewer axle counter sections but placed treadles at the strike in points. Remember that an AOCL is inherently safe; if the train fails to strike in for any reason then the DCI will be at red and the train will stop prior to the crossing; rather different to an AHBC!
Summary
Overall a good layout; you tended to avoid too many glaring mistakes. The fundamental questions the examiners will be asking are:
a) is it understandable?
b) is it practicable?
c) is it safe?
d) does it address the operational requirements?
e) is it economical?
Not perfect in any of these, but broadly the answer is yes.
In particular you read the operational notes that many seem not to do. You have a reasonable attempt at almost everything and generally avoid committing the worst howlers.
For the exam you obviously need to concentrate on TIME MANAGEMENT and this is far more important than any nuance of understanding.
If I had to identify six things that you should (in the limited time now left!) learn from having attempted this paper they would be:
1) A main / warning route must always be to a main aspect fixed red or a bufferstop
2) Track Circuit Block requires a signal at the place of reversal
3) There is a difference between reduced and restricted overlaps
4) Numbering of double junction point ends
5) "Standage" does not necessarily imply ability to run around train
6) Trap points are for freight lines against passenger lines or sidings against running lines
Other than that it will all be down to how you perform on the day- you have sufficient knowledge, but how long does it take you to get the plan done
So don't study too hard this week- get some rest and relaxation to be in a fit state to sit the paper.
Good luck
PJW