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2000 Headway Calcs and Layout
#21
(20-07-2010, 10:29 PM)PJW Wrote: The question I have though is:
how do you envisage that the freight that runs from A to B is to operate?

I'm still digesting some of the comments, but I'll answer the last question first.

For the freight train my intention was that the train from A comes onto the Down Main and leaves the wagons here, behind signal 123 (at night so ok to leave on the main line/saves the energy wasted in having to haul them all the way to the station only to come back again). The loco continues to station D, and then up to 1003 LOS, reverses and continues on the main line via 134 all the way up to 120 so that it's behind 1001. From 1001 shunts up to the wagons/behind 122. Then from 122 goes back onto the Up main and continues to B.
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#22
As said before, in general ok and a good minimalistic presentation for the exam- probably worth though having another column for main aspect / PL.

1. I believe you should have put Auto Facility on mre troutes; 127A9M), 134B(M) for e.g. but this is minor.

2. You have provided some shunt routes for no obvious reason such as 127A(S) where there is 127A(M)- see earlier post in thread re provision of shunt moves and running moves. Ironically the one that would have been useful was the one you didn't provide: 125A(S)- see the post re operation of station D and the inability to signal the loco back onto its freight train after the runaround move.

3. When having a route to a LOS, then the generally accepted indication is "X" to denote a "wrong direction" move- particularly if propelling a train, a driver has to be particularly careful not to overrun a ground mounted signal and needs specifically to be on the look out for it rather than looking high for a main running signal and this "X" is supposed to be a reminder of that.

4. I think you must be a bit confused re route classes in the UK- perhaps there is a bit of Australian practice to get out of your system....
A (S) class route is for shunting; not for use by a passenger train (except possibly as Empty Coaching Stock when not in public service). Signals 132 and 134 definitely need Main class routes into the relevant platforms including the bay platform. You might also choose to provide Call-on class routes (which display a PL but are distinct from shunt routes) to authorise a passenger train into an occupied platform where such a method of working is necessary and justified.
There is nothing in the station working that demands such (e.g. the joining of separate trains) nor is there any hint that there needs to be platform sharing by different trains to achieve the train service defined. Probably worth an assumption statement one way or the other; in this case it seems that the platforms are only as long as the passenger train length so to me that would be the final piece of evidence I'd use to say ASSUME NOT.
However had there been some reference to the stopping passengers only being 100m, then could well have said that providing call-ons into the bay would permit a service from G to F and also one from F to G both to be accommodated there for a short while, clear of the Down Main to let an express through before departing in quick succession to take the opposite directions at junction E. In such a scenario could be really useful to provide that facility even if rarely used (i.e. when all trains running to timetable not needed but invaluable to minimise effect of service perturbations); obviously in this case since two trains won't both fit then the idea would be a non-starter.

125A(W) isn't needed (see earlier post in thread re the ROL provided being of no value in this case)

Overall though these route boxes themselves were fine- it was just that they revealed a bit of weakness of your understanding which hopefully the above should help strengthen.
PJW
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#23
127 and 129 need to be platform starters and given the braking distance constraints then 131 falls wher it does which is fine, but I think that I'd have opened up the spacing to put 133 further away (to meet headway and overbraking but be more economical) and also indicated a further signal (not to scale) at the interface at F [generally plans nowadays show a specific NTS little portion- if so then use it to show the next signa and dimension it, I think it is good to show this owned by adjacent signalbox].

I'd have attempted to place 125 closer to the station (whilst honouring reasonably equal spacing, it is sensible to use the flexibility of 4 aspects to engineer a slightly shorter section on the approach to a staion where trains stop to counterbalance this a bit to mimimise headway impact. Also since we need a PL here and a long slow move to get the loco back on the freight train if we can make this say 800m rather than 1000m (and obviously compensate by the section behind being a bit over 1000m to be able to get minimum braking) then that is another gain.

Certainly a good idea that 123 is sufficiently beyond junction that a 400m long freight train held at it doesn't foul junction C- when you have thought of things like this, then worth while annotating plan showing a line backwads from the signal to show that you know you have achieved standage, rather than let th examiner guess whetheer or not that was a fluke!

121 is quite a bit away from the junction; if it could have gone a bit closer then that would have been good- however if not then it is ok where it is. As befoe I'd have shown in the NTS area at B the signal in rear, again at the biggest acceptable spacing.

I think I'd have put 101 closer to the junction. Parallelism with 121 isn't an issue as the line is almost certaily coming in at an angle and there would be no intervisibility and not on the same formation- recognise that the plan depiction is purely diagramatic in this regard. Braking isn't an issue as the speed restriction over 503R is only 40km/h. Hence 'd have decided upon the length of the overlap suitable (calculated TPWS effectiveness for a freight train to have a good chance of stopping prir to derailing at traps) ad then worked back t o place the signal which I'd habve made 3 aspect. Since we only have one train an hour and the line speed is 100km/h I certainly don't need a section signal in rear very close, so I would have put a Yellow/Green at (freight @ 100km/h) braking distance back and then at the NTS portion near "A" have indicated the position of the Red/Green as being "where required to protect any infrastructure hazard but perhaps 25km away"

I wonder which signal you placed first in the oposite direction. You have 128/130 at the platform ends which are fine, but they don't actually need to be there, so these would not have been constraints.

Junction C is more of the issue; you have 124 in a good place, however there are options such as putting it closer such that its overlap fallsbetween 505B & 504 (since 505 only used by the runaround freight by night then locking them in overlap is hardly a disadvantage) or even closer and have an overlap oint between DH & DG [funny- it looks like one on your plan- perhaps you investigated such an option....]. The reason for moving it would be if it gave advantage elsewhere.
My motivation is that I feel 134 is toofar from station D, given the regular stopping trains that need to crossto the Down side platforms to reverse. Approach releasing 134 and then continuing for a long way before reaching the first se of points across which to diverge isn't good signalling; I'd like to get 134 much more into the area of 132 and then place them exactly parallel. If the cost of doing that is to slightly complicate the locking (note that with swinging overlap it is not in the slightest operationally restrictive) at junction C then that is a small price to pay. Moving 128/130 off the platform ends by at least 200m so their AWS falls outside the platform is actually a good thing- gets rid of 128 as a platform starter and the associated SASSPAD risk.

Whereever I ended up placing 124 then I'd place 122 opposite it (but made a 3-aspect provided I'd satisfied myself re attainable speed at 120 for waring of the next red). I'd then put a Yellow/Green distant for 122 at suitable braking distance and change 130 to be a Red /Green and hence made this part of the line reversibly signalled for that night freight movement to avoid that propoelling move to LOS on the Up Main on the grounds of a) improved safety, b) considerable time saving and put a note to taht effect to justify my decision.

Otherwise similar comments re placing signals at fringes and I would have shown isolated 3 aspect (stop and distant) on the freight line and probably 3 aspects spaced a bare minimum braking on the line to B (which after all was what the calculations suggested would be possible in a plain line section)
PJW
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#24
(21-07-2010, 10:34 PM)interesting_signal Wrote:
(20-07-2010, 10:29 PM)PJW Wrote: The question I have though is:
how do you envisage that the freight that runs from A to B is to operate?

I'm still digesting some of the comments, but I'll answer the last question first.

For the freight train my intention was that the train from A comes onto the Down Main and leaves the wagons here, behind signal 123 (at night so ok to leave on the main line/saves the energy wasted in having to haul them all the way to the station only to come back again). The loco continues to station D, and then up to 1003 LOS, reverses and continues on the main line via 134 all the way up to 120 so that it's behind 1001. From 1001 shunts up to the wagons/behind 122. Then from 122 goes back onto the Up main and continues to B.

Excellent solution; I agree that it saves energy, time and signalling.
However do you see how easy for the examiner to fail to see that, because you gave no hint of your intention?
Agreed the signalling to do that was there, but there were also a few hints that seemed to contradict. Positioning of LOS seemed to allow a whole freight train to be propelled behind 134, not just to accomodate a light loco or a multiple unit; whereas it might certainly be useful to have the ability to do this in extremis (e.g. taking a defective wagon out of the centre of the train and setting back into the siding for rectification later), because you didn't explain it seemed to suggest that this was the route the freight would nomally take and hence influences the examiners' assumption of your intentions. Then taking into account the facts that
a) you provided some (S) class routes on the layout that were not needed / inappropriate (see Route Tables) adds to the general feelling that you were rather hazy in this area.
b) The signalling of the junction E with a signal missing and 132 without a distant makes it possible that 122 is in same category.
Hence rightly or wrongly the various other defects of your layout are taken into consideration when trying to establish what might have been going through your mind in this instance.....

So I judged you unfairly and would have marked you down incorrectly. The examiners do not have this opportunity for dialogue to probe your understanding and can only judge on what is actually presented. A brief note on the plan re the operation would have made all the difference (to be fair I can see a note near 123, but on my print out at least I can't quite read so the penny didn't drop. It does include the word standage so perhaps this is it and I apologise).

Actually overall the plan was really very good for a first real attempt I can see that you have considered the various trains listed in contracted paths (even though again I have difficulty (resolution of scan, faint, print size and my eyesight) exactly what you have written. You didn't really address the "Methods of Working" sufficiently though-
you show the OTW-NS on the Branch but could have put a sentence of explanation,
didn't declare TCB on the rest of the layout
should have added a few words re assumption whether permissive wotking in the station needed, any assumption re the move to the LOS / use of the Up siding and the operation of the night freight would have rounded things off and potentially saved being misinterpreted.
PJW
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#25
Peter
Do you have the time to write a small step by step guide on how to draw a stopping time-distance curve. I understand what it shows me in the study notes but am struggling to create one by myself. Any guidance you can give would be greatly appreciated.

Many thanks
Ian
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#26
Actually re-reading the notes again and again I think Ive nearly grasped it Ill try out on some graph paper as suggested.
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#27
(01-04-2013, 07:48 PM)merlin89 Wrote: Actually re-reading the notes again and again I think Ive nearly grasped it Ill try out on some graph paper as suggested.

You should also find some examples on this website- indeed for example in this thread http://irseexam.co.uk/thread-436.html
PJW
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#28
Have made an attempt on my 2000 layout stopping and non stopping calcs and even after reading all the replies above. Still not there yet especially the distance time graph. I would appreciate any feedback. But will attempt another one or two before starting on layouts.

Distance/Time graph added


Attached Files
.pdf   2000 Layout Calcs Page1.pdf (Size: 433.46 KB / Downloads: 34)
.pdf   2000 Layout Calcs Page2.pdf (Size: 506.63 KB / Downloads: 23)
.pdf   2000 Layout Calcs Page3.pdf (Size: 456.42 KB / Downloads: 21)
.pdf   2000 Layout Calcs Page4.pdf (Size: 398.36 KB / Downloads: 20)
.pdf   2000 Layout Calcs Page5.pdf (Size: 269.01 KB / Downloads: 23)
.pdf   2000 Layout Calcs Page6 Distance Time Graph.pdf (Size: 747.38 KB / Downloads: 22)
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#29
First question-
do you mean 2001 as per file name or 2000 as per the heading on your sheets; the numbers seem to make more sense against 2000 so that is what I assumed you meant.

“Determine theoretically, either by calculation or graphically, appropriate signal spacings for the braking characteristics and the intensity of traffic on offer. All calculations and graphs must be shown”
• Don’t waste exam time by re-stating question unnecessarily

• Freight max speed is 100kph; therefore if calculating the constant speed headway at 120kph it is clearly irrelevant; therefore the maximum train length that should be used in calculations is 200m

• Not sure what was the relevance of stating 3 aspect signalling system so early on’ the selection will be driven from the numbers that are being produced.

• Assumptions ok, but should explain more re the contingency allowance made. Given the low non-stop train service, seems a large allowance- obviously makes more sense in the C-D portion where there is the convergence of the two line and also the stopping traffic, but even so needs justification.

• Diagram and formula for best possible 3 aspect headway fine

• Having stated that 3 aspects spaced at 2000m would just meet the requirement with your assumed level of contingency, then I don’t see what the lower half of page 2 and page 3added. You have severe time constraints in the exam- do not waste it! You are basically doing the same calcs again- it should be obvious that increasing spacing to 2000m from 1975m is a minute percentage overbraking so that really is not a consideration- indeed just having 25m tolerance re placing of signals is in reality no flexibility at all. Hence either need to give less contingency or would in practice be forced to use 4 aspects. You were doing ok for the first 1.5 pages; actually thereafter not only were you not gaining marks but actually were showing me that you probably don’t really fully understand- what you wrote was ok, but you were basically doing something that did not need to be done.

• Stopping calcs would have benefitted from diagram- page 5 refers to graph that I have not seen yet

• t2 is basically assuming that braking will not commence until the last possible time and that will then to come to a stand in the platform; you have not considered the cautionary aspect sequence that the driver may have received prior to this (which indeed is what t1 is all about- being on the approach to a signal prior to the station which is still showing a restrictive aspect due to the earlier train still being in the platform or only recently having departed.

• t3 and t4 ok- though obviouslyif the train is starting 25m before the signal then this should have been what was taken into account when considering t2 earlier!

• You have not explained, possibly because you have not understood, the significance of calculating t4 to be the time it takes the train to move beyond the overlap of the signal (which you are implicitly assuming but have not stated to be at the end of the platform). You are stating that the headway time can be calculated as t1=t2+t3+t4 = 148s but you have not explained this and indeed then you state that the minimum time spacing between the trains is 163s- this surely is what is meant by headway time, so you have failed to explain a missing term- (let’s call it t5) that adds those 15secs. I am guessing that you are assuming 3 aspect signalling at 1975m/ 2000m but again you have not stated.

So to actually answer the question that was asked having done both sets of calculations,
• what is the appropriate signal spacing?
• Is it the same for the whole layout area?
Don't think that your answer included a clear statement about these so although the cals were there stopped short of a final conclusion.




(06-04-2013, 01:16 PM)merlin89 Wrote: Not so sure about my calculations here. Any feedback appreciated.
PJW
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#30
Peter,
Many thanks but i think you may have mixed up the files to two threads I have recently uploaded answers to, one for 2001 and one for 2000. apologies for the confusion.
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