(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
105A(M) OK
105BM)
Well done for providing the route as requested.
However a GPL or LOS cannot be the end of movement authority for a main aspect move. Since this is passenger movement then it does need to be a main aspect move and therefore signal 505 would need to be a main signal. In this case it would just be a fixed red aspect, but on a full sized post etc.
In a different scenario where the stabling siding were beyond it (rather than as here requiring a set-back move) then the fixed red would also have an elevated PL to permit the empty train to proceeed to the siding.
Should have shown as MAR.
106A(M)
Well done for realising that the train from the Lake Branch would be using this line in the contrary direction and providing a signal for it to access the Down Valley Branch.
Provision of a SARI seems sensible; some would provide it a PLJI because of the nature of the junction. Standards do change and there is a lot of "preferential engineering" about, but I am with you on this one but I think I'd have chosen to display "B" for branch to reinforce message that train isn't to continue in Down direction along the mainline (but obviously driver with route knowledge ought to be well aware of the track layout!).
However I do not see the need for 106A(W). In fact the only overlap I see beyond 204 is what is marked with an overlap symbol and 60m. This implies to me that you are attempting to justify a
reduced rather than
restricted overlap.
Since the turnouts at each end of that portion of the Down Valley Branch are only 40km/h (=25mph) then you could have chosen the define the permissible speed on this whole section as 40km/h with no detriment to operations. This could perhaps then be your justification; the chances are quite good that TPWS would stop a multiple unit passenger train within that length. Since it does not appear that freights will use this route, then you could well have a good argument [but you should have put some relevant note on diagram or route box to have explained]. Such an overlap would be associated with a (M) route not a (W) route. See
this explanation of reduced v restricted verlaps
HOWEVER, on the assumption that you actually meant this as a ROL and that you intended a full overlap further along the line (say at the end of the viaduct), you need to ask yourself what would be the advantage of this ROL? Basically nothing; both the ROL or the O/L lock 703R and the only advantage for locking a shorter length of railway would be if it enabled that length of railway to be allocated to an opposite direction signal and thus permit a Down train to approach closer to station C than otherwise possible. This is not the case here; if there is no advantage resulting from either a reduced or a restricted overlap then just provide a full O/L.
In the situation where a (W) route is provided, then the approach release would certainly require track occupied for a time- say 20 sec as a good "stab in the air" ballpark figure without worrying about measurements.
108A(M)
All turnout speeds are 40 km/h, so should have been MAR not MAY-FA.
108B(M) OK
108C(M)
Rather confusing I think to give pos 4 PLJI and still end up to the left of the straight route. Although as signal engineers we could check the "small print" of the rulebook and argue that technically compliant, we should perhaps consider the driver and human factors a bit more. Having chosen a SARI for the parallel signal, then why not use a SARI for this route as well and give the same indication for the same destination?
This gives further rationale not to use "D"; I think we could still get away with "B" since the A route uses a PLJI, but I am beginning to wonder whether we may need to go to a two character display "DV"- saves any ambiguity, but are large and can be difficult for signal structure, sighting etc. I think I'd propose to the operators that this portion of the line would be better designated "Branch Loop" and the adjacent line "Branch" as they are both bi-directional and distinctly different in nature to the lines the other side of the viaduct. I could then use a SARI for the A route showing "B" and a SARI for the C route showing "L" and change 106 to "L" as well.
Don't be frightened of proposing that sort of thing when signalling the layout- it shows common sense and experience rather than slavishly following that with which you are presented.
What you did was not wrong; it is just that it could have been better.
C route should be MAR whether PLJI or SARI.
111A(M)
OK. The only potential issue is the method of working proposed for the Lake Branch. Since your general notes say generally TCB and don't give exceptions and since there seem to be track circuits then I'll assume TCB. however I do notice that there isn't a signal at station F to authorise the return journey so warning bells are sounding. If there was to be some other means of controlling the directional use of the line such as token, OTW-NS etc then there should have been a note in comments column of route box for this rout.
111B(M) OK
201A(M) & 201B(M)
There is a mismatch somewhere. Two routes, different destinations but no route indication to the driver re where the train is going!
Also I see that the next signal is 203 but also this is just a distant and given a deta late accordingly, so ok so far BUT it also has a PLJI !!!
Unless you are to have another section signal between 201 and 205/207 then the route indication needs to be given at 201.
Also if you do feel you need 501 then these routes will need to pre-set it accordingly.
203
There are posts earlier in this thread re positioning signals on this stretch of line. Several competing factors:
a) don't want to stop train on viaduct if at all possible
b) don't want a signal on the viaduct if we can do without- difficult an expensive to design / install / maintain
Ask yourself what it is for- as you have drawn it then can only be to give warning to brake.
Could it be moved to the beginning of the viaduct- if it is a little overbraked in this scenario does it really matter?
Could 201 be made a 3 aspect- again just how overbraked would that be?
Could we provide 203 as a 3 aspect and just provide controls that prevent 201 from clearing unless it is already off (or at least "ready to clear" and thus no longer worry re the lack of braking from 201 to 203; if so is it best placed where it is, or at the start of the viaduct, or perhaps position at the far end of the viaduct but perhaps re-think what special controls are applied to which signals?
205A(M), A(S), B(M). B(S)
Same comment as 105B before re 505 needing to be a full red aspect.
Not really sure why you felt you needed a (S) and PL to enter the main line platform as there is no hint that the 20m trains are actually composed of two 100m units but this is possible so not a bad idea, though is best to add a note re your assumption. You haven't provided a similar route to the bay platform, but that is rational since any such movement would be from the stabling sidings which can access the bay directly rather than shunting via 205.
Now that I seee you have used "B" for this SARI, it explains why you didn't want to use this designation for 106.
207A(M), B(M), B(S)
A SARI for each main route is sensible, but you have not declared the character displayed. To be honest I think that I'd have numbered the platforms 1,2,3 and then that means I can use these numbers for the route indicators that tends to keep things simple.
No idea what the B(S) route is about; it would surely be the C(S) if it existed at all but there is no other pointwork and most certainly can't read into stabling siding!
501
I wouldn't have had this signal at all; I believe that you thought you needed this and 502 because of your misunderstanding re standage discussed earlier.
Let us asssume though that we did want a runaround facility; 501 would then be needed (unless you did modify 203 to be somewhere at the end of the viaduct and you could then add the relevant PL to that structure and this would appear to be a better solution).
I think that a MARI for this PL or GPL would not actually be required and thus provision is rather superfluous.
502
Even with 501 where it is, 502 is rather unnecessary. The train may as well be signalled as far as 202, the driver knowing what is required of them will just get behind 501 and change ends ready for that signal to clear. Having said that I suppose that it could be justified if such a runaround a regular feature. This would be because the viaduct section is clearly a bottle-neck constraint on capacity and minimising occupation time therefore important. Provision of 502 would allow a locomotive to follow whilst the previous up train still on the viaduct and get itself behind 501 and routed back on the other line snappily without using up any more line occupancy since any train at 201 would have to be waiting for the up train to clear 701 anyway. I think that you probably didn't think it through that deeply, but I can't be sure and neither would an examiner. So although your note re standage showed a misunderstanding, it is paying dividends here since when looking at your layout I understand why you have placed 501 and 502 and given your understanding then they look very sensible rather than looking wrong otherwise.
The problem with 502 however is that you have not provided PL aspects and (S) routes on 204 / 206 to authorise moves up to it at danger and indeed the (M) routes from those signals would need to pre-set 502.
A further rationale for 501 could be to meet the requirement that ECS trains can shunt from all platforms to / from stabling siding. However you try, the track layout makes this convoluted from the Down Main platform (and is why the requirement specifies the terminating trains to use the Up platform no doubt).
Your introductory notes probably should have described how this move was to be ahieved. Choice seems to be:
a) pass 106, reverse at 207, reverse at 108, reverse at 205, reverse at 208 / 504, or
b) pass 106 and 204, reverse at 501, pass 205, reverse at 208 / 504.
Neither is good- the driver will certainly not thank us for solution a and may well be tempted not to change to the leading cab and therefore make high risk propelling movements. Solution b uses up line capacity on the viaduct single line and isn't an option if a freight is being held in either loop. I think my approach would be to explain that it is a P'Way rather than signalling constraint and whereas the move is possible, the station working would be at pains to ensure rarely need to make it. Therefore not worth putting in too much more signalling to faciltate; I think I might just have put a LOS on AD track so that a train terminated in the Down platform could be signalled out and use 105B route to go into the platform that it probably was due to terminate in but couldn't use at the time due to timetable perturbation.
Other GPLS
Not much to say, other than restrict use of MARI to where it is crucial that a driver knows where they are going before they start moving. I think that there is an argument for 208 (which I note didn't get a route box) and 504 to be given MARI (for both routes) to distinguih between running line and siding particularly as the driver is unlikely to see the lie of 705 points when at the signal, but otherwise I think no SARI needed.
In the exam you won't have time to do every route box so concentrate on the most complicated area and do a few dissimiliar ones to
a) help the examiner understand your signalling
b) demonstrate that you can fill them out correctly. To save time I might omit the destination line as the exit signal actually covers it although that does make the examiners job a little more difficult of course
