2008 - CT

[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.