2008 - CT

[PJW]

Comparing my work to his, I also have some confusions:

1. 147B(S): requires TC clear, do not requires CJ and CH clear? My answer is "CP, CN CL, CK, CJ, CH". In the opposing route locking, it indeed usually does not require overlap TC clear for the shunt route.

Basically you need to think what the route is FOR. If you assume that it is to shunt an entire train that arrived in the Platform Loop from the north curve and now needs to be put in the Up platform, then proving all tracks clear in the route is tenable. Therefore to modern standards you'd be right to include CJ and CK as well, particularly as plan shows this as explicitly a shunt overlap,; however be aware that until a few years ago, overlaps for shunt routes would not have been proved.

However if you think that the route may at least sometimes be used to take a short formation train, perhaps originally from the Up siding and run via the Platform Loop onto the Up Main, in order to set it back onto a short train already in the Up Platform then the omission of CK, and possibly also CL ,would be essential; proving an overlap clear in such a situation doesn't make much sense.

Generally therefore what to the signaller a shunt route is often within the interlocking itself two separate ones:
a) a non-permissive (selected by CL and CK clear) which comes with an overlap as you have shown, thus getting maximum safety when thi is possible
b) a permissive (selected by CL or CK occupied) where only the minimum number of tracks are proved clear, thus enabling its use to join trains together and gaining operational flexibility when it is needed.

So you need to look at the layout, decide how it would be operated from what clues there are around, state an assumption that justifies the locking you provide. To be honest in this case I am struggling to see much need for the route at all; the main use could be to cross a train that has terminated in the Down Platform onto the Up to await time to return on the Up Main. However if only a short time then have running sgnal 156 for that; if a longer time and needed to clear the Down for other traffic, then use of 157 and the set back shunt at that end of the station to do this move would seem the preferable option.

So the simple answer is that you are right IF you stated that you foresee no need to use the route to join vehicles in the Up Platform

For your opposing route locking comment I interpret that you mean that the locking that this route IMPOSES on the up direction routes. Historically shunt routes didn't have overlaps and therefore you are right, but where overlaps are provided at aspect level I'd certainly expect in the opposing route locking. Indeed could well have the tracks included in the opposing locking even if not proved by the signal's aspect; I would interpret the plan in this case as meaning that they ought t be included (unless you state your railway's standards don't provide any form of overlap for shunts and therefore you will no be precisely following the plan in this regard)

2. 147B(S):
for the opposing route 164B(C ), my answer for 164B(C ) is "CF,CG,CH,CJ,[CK,CL clear or 9CKorCL occ for 30s0]".
Am I wrong?

147B(S) needs to ensure that any train previously authorised to take routes from 164B(S) has either:
a) gone away completely, or
b) has timed to a stand in the platform so that further vehicles can be safely added to a stationary train. This does of course is only valid if you are not proving all tracks clear in the shunt route's aspect level; otherwise it it is effectively as per a main route and therefore only option a is applicable. The route should NOT set if the aspect isn't ever going to clear.

This is one reason why I would recommend adopting the older standards for shunt routes; many of us including the IRSE examiners have been around for a few years and were brought up with the older standards and therefore initially expect them. Adopting modern standards means that there is little real difference between PL and main aspect moves, so an opportunity for the student to demonstrate their knowledge is lost.

Certainly you must be consistent; the inclusion of "or occupied for time" in the opposing locking for a shunt route requiring the same tracks clear indicates that the candidate really doesn't understand what they are doing!

It is however perfectly reasonable to set and lock an overlap at the route setting level which prevents opposing / conflicting moves in it but not actually depmand those points detected and the relevant tracks within the overlap clear within the aspect proving level. This way you get almost all of the safety in the event of a SPAD at the exit signal (though obviously inevitably with the equivalent loss of layout flexibility in operation that this implies) whilst minimising the chance of a failure preventing the aspect clearing.

If you are giving shunts overlaps then the opposing route locking should include proof that FE has been cleared ( note that this locking isn't by passed by occupancy for time of FD/FC) even for an opposing shunt route whose aspect does not prove those track clear.

3. 124B(M): 166A(S) and 164A(M/C) do not have common overlap. So why should require them as opposing route locking?

124B(M) only reads to 149 and you are right that its overlap only includes FG. Therefore it is permissible to set routes from 166A simultaneously as the overlap does only include FE. Hence wouldn't need opposing locking between these, so you are correct.

4. 161A(M): Why the opposing route locking require 149B©? I am confused about which situation it belongs to?

161A(M): actually this isn't opposing route locking but GK/RT0044 locking sometimes (but actually erronously though the name has now stuck!) called "Huddersfield". The intention of this is that if a train entering a platform has been given a PL aspect because a call-on route has been set, then the first train already in the platform is then deliberately trapped there; hence the second train will actually find the platform occupied.

a) The call-on route requires that all routes from the platform exit signal are not set.
b) The routes from the platform signal require that the call-on route isn't set and any train on that route has reached the platform.

Actually there is often somewhat greater complexity than this re attempting to prove that it is really at a stand, which can be very involved given that there can be a range of scenarios re which tracks were initially occupied or clear depending upon the length of the first train already in the platform and the second one joining, or indeed it could even be a third one....... In my view this has just got silly in the real world and is certainly FAR TOO FAR for the IRSE exam. Potentially you could adopt practices that don't have this locking at all; I think I would recommend putting something in, but keeping it simple and to the essence as I have described above.