2008 - CT

[greensky52]

Your explaination is simple and easier for me, haha. I think I have got what you said. But maybe I will try on another year's paper and post my answer here, you can see whether I really understand.

Anyway, thank you.

Referring to item 1, I am not sure I have got your point. In short, do you mean it should be decide by the actual situation of shunt route?

If the shunt route is for a pemissive movement, it is no need to consider the overlap. Such as shunting a train to couple with another one which stop in the platform?

If it is an unpermissive movement, overlap have to be considered for safety. Such as wrong direction movement?

In short Yes, there is no one answer for shunt routes-
a) sometimes they prove all tracks clear and have overlaps (just as if main routes),
b) sometimes they prove all tracks clear in route itself but not have any overlaps at all,
c) sometimes they prove all tracks clear in the route itself but not in the overlap yet still lock an overlap
d) sometimes they prove only some tracks clear in the route itself and would therefore have no overlap at all.


In general signals are approach locked when the signal clears.
For a main signal, occasionally it is worth providing "comprehensive approach locking" such that the locking is only actually imposed (or can be immediately released) if all the tracks are clear back to the sighting point of the furthest signal which changes aspect when signal concerned is replaced to danger. However it can be expensive to provide and takes time to test, so only provide where particularly useful.

Conversely a GPL signal is only visible for a short distance and the maximum speed of train approaching a GPL is only 15mph. Therefore comprehensive A/L is "always" provided (since it is cheap and simple).

[greensky52]

1 In opposing route locking of 164B(M):

I think 166B(S)&162B(S) are both necessary, because a train starts from 166, after it clears point 257A, it will appears on CH--it may be a rear-end collision, right or wrong? I feel I am a little confused about route locking.........


2 If we use NR standard, it needs not consider OL for shunt route. But if there is OL for shunt route in layout diagram, do we need to state in advance"prove all TC clear in the route itself but not in the overlap but still lock the OL "?

Or could we state that we do not consider the OL althogh there is OL in the layout for shunt route because it is simplefor written?

[PJW]

1 In opposing route locking of 164B(M):

I think 166B(S)&162B(S) are both necessary, because a train starts from 166, after it clears point 257A, it will appears on CH--it may be a rear-end collision, right or wrong? I feel I am a little confused about route locking.........


2 If we use NR standard, it needs not consider OL for shunt route. But if there is OL for shunt route in layout diagram, do we need to state in advance"prove all TC clear in the route itself but not in the overlap but still lock the OL "?

Or could we state that we do not consider the OL althogh there is OL in the layout for shunt route because it is simplefor written?

1.After a train from 166 has cleared point 257 then indeed this can be moved and the route from 164 can be set. Obviously though the aspect will not clear as the track circuit is occupied. Network Rail allows the setting of a route when the tracks are occupied; it is no different in this case than if the first train had itself come from 164. Indeed once we are in this situation then it is really no different to an auto signal; we hae eliminated JUNCTION RISK and all we are now worried about is TRAIN SEPARATION. Yes if the train at 164 SPADs then a rear end collision may well result, but what is different about that. Remember that (other than possibly seeing / hearing certain points move) the train driver has no idea whether the ROUTE is set; what they know about is the ASPECT and that has not yet changed from red.


2. You may certainly follow any sytandard with which you are familiar, but do state what this is. The current NR standard is to provide overlaps for shunts when used non-permissively, both LOCKING and ASPECT. You are correct that in the past, generally shunts were not given overlaps at all. Sometimes though we did LOCK aet and lock an overlap but not actually prove point detection or train detection.
So you could state that
a) practices with which familiar do not require shunt overlaps, so these designations on the layout have been disregarded in these Control,Tables, or
b) practices with which familiar require shunt overlaps only to be locked but not proved
for example as a means of informing examiner the context in which they are marking.

[greensky52]

All noted.

Thanks a lot.