1) In essence, yes.
Your headway calcs are (I guess) based on all trains non-stopping travelling at 120km/h, but of course if you consider those 5 trains then 2 of them stop and 1 is a freight (with a lower maximum speed of 100km/h). Hence whereas 2 of the trains will occupy one train path each, the other 3 will eat up a bit more capacity than you might oversimplistically be asssuming.
It may well be that 3 aspects will still be enough but you should make sure that there is a fair bit of contingency over and above the 5 trains per hour.
Thinking about the stopping service, if you do a crude estimate and state that for every station the stopping train will lose say 90 seconds (in slowing down, at reast and re-accelerating) compared to the through service then that's nearly 5 minutes extra overall. Hence if your signalling only provided for a non-stop headway of 12 minutes (in order just to achieve 5 non-stop trains per hour) then your two stopping train would actually be sing up broadly three such train paths between them and the freight wouldn't be able to run as it too will use more than one train path as it travels at a slower speed.
If however you provided signalling to give say a 8 minute design headway it sounds much more acceptable and you could envisage:
a fast train at 00
a freight train at 09
a stopping train at 18
a fast train at 30
a stopping train at 48
this clearly has plenty of capacity and doesn't over restrict the timetable planners who have to juggle different constraints like these all around the railway.
I haven't done the sums but merely guessed, but assuming that is all the capacity we want,then it may be that we do not even need continuous 3-aspect signalling; isolated 3-aspect (i.e. stop and distant 2 aspect signals) may well be adequate.
However do not be a slave only to headway; think where you need signals to protect hazards such as junctions and to be operable (so reasonably close to pointwork, ability to have the routes needed).
You are bound to need signals at the end of the platforms at E and you'll also want a signal only about 700m prior to that (in order to protect the station throat)- you'll need to figure out how that accords with the braking distance requirements and what to do about any incompatibiity between that and the optimum position from a junction protection perspective.
Similarly you have other more-or-less fixed signal positions at the end of platform 2 at G and on the Up Main approaching that junction from the right. Somehow you need to juggle things so that you can place signals where you want them at these sites and get an integral number of signal sections separating them, whilst abiding by the braking & aspect sequence considerations. Certainly you must make sure that the headway requirements are also achieved, but given these are not onerous, I suspect that the signalling will be more determined by the spacing of the layout features.
2) For the re-occupation time on the single line you need to calculate how long it takes train 1 from the time it leaves platform 2 at E to travel the line, accelerating, decelerating, dwelling at intermediate stations as required, then its 5 minute turn-round time at B and returning similarly until it gets clear of the long crossover (via the switch diamonds) into platform 1 thus enabling train 2 to enter from platform 2 in order to do similarly.
Quite a lot of calculations, but look at the plan carefully as the examiners have been kind to you and you can use some of the sums multiple times.
I think this was the bit of last year's paper "that separated the sheep from the goats".
Obviously I don't know what twist there will be in 2013, but you'd be wise to expet something different, rather than the overly formulaic apprach that was the case for many years previously.
Your headway calcs are (I guess) based on all trains non-stopping travelling at 120km/h, but of course if you consider those 5 trains then 2 of them stop and 1 is a freight (with a lower maximum speed of 100km/h). Hence whereas 2 of the trains will occupy one train path each, the other 3 will eat up a bit more capacity than you might oversimplistically be asssuming.
It may well be that 3 aspects will still be enough but you should make sure that there is a fair bit of contingency over and above the 5 trains per hour.
Thinking about the stopping service, if you do a crude estimate and state that for every station the stopping train will lose say 90 seconds (in slowing down, at reast and re-accelerating) compared to the through service then that's nearly 5 minutes extra overall. Hence if your signalling only provided for a non-stop headway of 12 minutes (in order just to achieve 5 non-stop trains per hour) then your two stopping train would actually be sing up broadly three such train paths between them and the freight wouldn't be able to run as it too will use more than one train path as it travels at a slower speed.
If however you provided signalling to give say a 8 minute design headway it sounds much more acceptable and you could envisage:
a fast train at 00
a freight train at 09
a stopping train at 18
a fast train at 30
a stopping train at 48
this clearly has plenty of capacity and doesn't over restrict the timetable planners who have to juggle different constraints like these all around the railway.
I haven't done the sums but merely guessed, but assuming that is all the capacity we want,then it may be that we do not even need continuous 3-aspect signalling; isolated 3-aspect (i.e. stop and distant 2 aspect signals) may well be adequate.
However do not be a slave only to headway; think where you need signals to protect hazards such as junctions and to be operable (so reasonably close to pointwork, ability to have the routes needed).
You are bound to need signals at the end of the platforms at E and you'll also want a signal only about 700m prior to that (in order to protect the station throat)- you'll need to figure out how that accords with the braking distance requirements and what to do about any incompatibiity between that and the optimum position from a junction protection perspective.
Similarly you have other more-or-less fixed signal positions at the end of platform 2 at G and on the Up Main approaching that junction from the right. Somehow you need to juggle things so that you can place signals where you want them at these sites and get an integral number of signal sections separating them, whilst abiding by the braking & aspect sequence considerations. Certainly you must make sure that the headway requirements are also achieved, but given these are not onerous, I suspect that the signalling will be more determined by the spacing of the layout features.
2) For the re-occupation time on the single line you need to calculate how long it takes train 1 from the time it leaves platform 2 at E to travel the line, accelerating, decelerating, dwelling at intermediate stations as required, then its 5 minute turn-round time at B and returning similarly until it gets clear of the long crossover (via the switch diamonds) into platform 1 thus enabling train 2 to enter from platform 2 in order to do similarly.
Quite a lot of calculations, but look at the plan carefully as the examiners have been kind to you and you can use some of the sums multiple times.
I think this was the bit of last year's paper "that separated the sheep from the goats".
Obviously I don't know what twist there will be in 2013, but you'd be wise to expet something different, rather than the overly formulaic apprach that was the case for many years previously.
(21-08-2013, 09:50 AM)DLMC Wrote: I would like to ask two questions about 2012 calculation
1) In question 1b signalling system determination, the calculation of 3 and 4 aspect headway is around 120 seconds and 90 seconds respectively. How shall I determine the choice of signalling system? Shall I base on the number of trains per hour between D and H? i.e. 5 trains per hour and so 3 aspects is a cost effective solution to fulfill the headway requirement.
2) for the re-entry time, is it mean the stopping headway plus the 5 minutes of layover time at B?
Thanks
PJW