alexgoei Wrote:Do hope Peter can join in, clarify and comment on my answer especially the latest posted. The earlier submission of 9th July has not been answered but never mind it can be ignored.
Now back from a short holiday; too much in the inbox to deal with tonight as have only just got in and have things to do prior to early start tomorrow- I'll attempt to answer tomorrow night.
Firstly sorry I missed answering this one initially: you should have said! I suspect that I came back from away and another module 3 post had risen to the top of the list and this slipped beneath radar.....are there any others missed?
Re 234 deadlocking.
First I think you need to be careful in the direction of the locking. I actually prefer to put the "set by routes" as the first column so then the dead track locking is placed with all the other locking so this tends to reduce any N>R or R>N confusion. Particularly important when the straight route is R as in this case!
So I claim:
Locking N>R (i.e. preventing points being moved to straight lie):
CG, (BS or 233N),(EC or 235N) but both ED and CF are irrelevant
Locking R>N
CG, (CF or 233R)
I do wonder re ED as yes the very tip may well be foul of moves over 234N. However I don't want to lock 24 as the only overlap beyond 166 is via 234N and it is certain that the layout has been designed to have that overlap in use when another train is using the Down Branch (or else 235 would have been included within that O/L and indeed would have been numbered 234B instead). Therefore I'd be ensuring that 235 N>R would prove (ED or 232R) but not locking 234; remember that the main purpose of foul track locking is to prevent the signaller making an ill judged handsignalled movement on a path through the layout that seems to be free of trains yet something is overhanging the corridor through which the train is to pass. Only need to prevent one of the points getting into the lie for that movement, so I'd ensure that 235 protects and therefore 234 doesn't need to.
So re YLP's comment, for a handsignalled move along Down Main, the signaller needs only to key 234R and 232N; does not key points in overlap or flank, but only line-of-route. If the section of BS over 233R is occupied, there would be a collision; hence must prevent 234 going R, therefore BS is a conditional foul track for 234N>R.
Also why do you think that 234 should be route locked by 142D? I agree route locked by 142C as a shunt overlap is depicted beyond 166 and there isn't one along the Down Main but only towards the Branch- hence 234 must be set, locked and detected N. Indeed we'd want to be able to signal 138C up to 166 simulataneously with 142D up to 168; even if the very far ends of the two overlaps were foul of each other. Think about it; for a collision to occur requires 2 SPADs on PL moves to happen more or less simultaneously- liklihood extremely low, severity pretty small and the trains would hit anyway in a few more metres..... It is a bit unusual but there is a case at Labroke Grove outside London Paddington- introduced when we got some (shall we say exceptionally generous length) overlaps in the vicinity of SN109 after the accident.
Returning to other issues on 234 CT, I'd have expected 162C and 164B to call and lock 234N and 171 to soft call (i.e. call if free but not lock or detect) 234R as it would rather like to have flank yet the
layout suggests that ensuring that there can be no wrong direction move along the Down Main is the higher safety priority and thus it must yield.
Hope this has helped both of you re 234; 225 will have to wait until tomorrow evening I am afraid. Let me know whether the above has made sense or not......
PJW
PJW