(22-05-2009, 08:19 PM)PJW Wrote: ......my initial thoughts are:
a) not too bad for first attempt, looks reasonably clear and laid out. Personally I feel that slightly diagonal lines rather than pure verticals are clearer particularly where lots of lines cross
b) I notice that you have put a R+ROL so that is hopeful but it looks suspicious that the approach release on the signal in rear for the Warner seems to be the same time as that used for the routes with a junction indicator
c) aspect sequence from reading up to 194 at Green is certainly wrong- your diagram calls for the display of BOTH YY+4 and G+4 !
However I have seen far worse and so you seem to be on the right lines; the devil is in the detail however when actually checking it against the layout. That may have to wait a week, but perhaps someone else will be able to comment sooner.
#1
Perhaps not 100% essential but a denotation of an overlap symbol beyond each R is a good idea.
#2
You missed out 192 signal which is the distant for 194
#3
162 and 164 can therefore not ever show Y+JI pos 4; I do think that the route boxes provided are misleading but don't know if that was deliberate or an error
#4
I do find the central area of your diagram confusing. With purely vertical lines it is hard to work out whether for sequence from "top right to bottom left" or from "bottom right to top left". I prefer slanted lines throughout but if you can't do that (it does use up more width) then at least make the tail where it connects into the horizontal line at an angle rather than a right angle to give that sense of directionality. Indeed I don't think it was just me that got confused; I think you did as well- see later!
One thing that was definitely wrong was that 142 being a 3 aspect reading up to a 4 aspect would need to show G when 162 is at Y, YY or G; hence a single line from 142 must branch into two where it joins the 4 aspect sequence between 134 and 162 (as in that case the aspect at 134 is different depending on whether 162 is showing Y on the one hand or (YY or G) on the other. THIS IS A VERY COMMON MISTAKE TO MAKE.
#5
It is arguable whether122 should show YY+JI pos4 up to 142 at Y since given the speeds etc giving the first warning to brake by Y at 142 would be enough and thus 122 might as well show G+JI pos4. However it'll make no real difference how driver will drive their train and it seems unlikely that train would be routed non-stop through this platform from Up Main back to then Up Main again; in real life I'd be tempted to make 142 MAR and thus the best aspect on 122 would be Y+JIpos4 in that scenario. I don't think it matters too much what you do, but I'd advise a note on the diagram that lets the examiner know that you've thought about it.
#6.
You have correctly drawn the approach release for 122 MAR but you have implied that it is the same time as used for the W route up to the ROL beyond 134. Indeed to be honest the presentation is barely distinguishable from 118 routed up to 122 when off for the diverging route- this is another reason why I like diagonal lines for sequence and so can reserve purely vertical lines for approach release. In the exam you'd have A3 paper and so you will have more space (and remember if necessary you could split over two sheets if think would be too crowded- but you should normally be able to fit it on one).
Note the dimensions on the plan: length of BF+BG+BH = 650m. Reasonable to guess that BF=180m so let us guess that BG might be 220m and BH 150m. Since MAR should occur as soon as PLJI is readable I think that the approach release would be (BG or BH)occ as one could expect it to have reasonable visibility given that speed of line is 100kph. BH for time is pretty draconian approach release as one might use for the PL into occupied platform; I think BH occ might be the best choice for the Warning route approach release.
#7
You made your problem re #4 and confusion in the central area of the diagram worse by drawing 134's diverging route above the straight route and 136's diverging route below its straight route even though geographically both are actually the other way around. This has meant that far more aspect seq lines have had to cross each other than strictly necessary.
#8
You then joined up the "J4" lines from 134 with the "J1" lines from 136 which is certainly confusing since these read to different signals in advance. Indeed if you look at your diagram it certainly looks as if 136 reads up to 164 for both its straight and its diverging route, though admittedly this diverging route also seems to read up to 162. I am sure you knew what you meant but your diagram didn't convey. I suggest that a quick sketch before staring the diagram proper just showing the interconnection between signals and which are 3 and which 4 aspect sequences is a good idea.
#9
Unfortunately it is just in the area of maximum confusion so I can't be sure what is really happening but you have certainly had an attempt at the flashing aspect. I note that you have shown the approach release by a dashed line (that is a good idea as it distinguishes it from normal sequence and would therefore address one of my points in #6). The MAR is from the R which is correct and the MAY is from the Y+JI pos4 which is also correct (though this was a bit more convoluted on your diagram and not so immediately obvious). The FY on 136 and FYY on 122 and G on 118 are correct, so this part looks good, but note that until the MAY occurs that 164 would show Y+JIpos4 whether 192 at Y or at G. I am having to assume (because not very clear what you meant) that BR for t is supposed to be both for the MAR and the MAY. BR is 450m long so it is perhaps possible that the PLJI sighting may be less than that, so perhaps a small value of t might be needed, but perhaps it could just be BR or even ((BP or BR)occ.
There are a few extra notes that you could have put on to get another mark or so for the flashing aspect, but all in all it is pretty sound.
Hence given your newness to this then I think you can be happy with your effort. Just a little more thought re how you laid out the diagram before starting would have made it far clearer to read. You'd be less likely to make a mistake and the examiner will find it far easier to mark and thus be more impressed than if having to struggle to understand what you meant. I've tried to indicate a few things on the scan of your attachment but there isn't the space for me to amend fully. Best thing would be for you to attempt to redraw taking my comments into account so that you can learn by sorting out the tangle and we'll then see if you have comprehended everything.
PJW