21-07-2010, 11:41 PM
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)
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