2008 - CT

[PJW]

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.

The appropriate option depends on both:
1) the standards being adopted for your Control Tables
2) the specific layout and the operational use of the route.

Modern NR practice would be to use option a) whenever possible but use option c) as non-preferred option if need to use to join vehicles or even option d) if essential for flexibility.

Older practice would be use option d) almost always but use option b) if the move was effectively a running move from a PL signal (rather than a true shunting move). Option c) woul;d be used if a specific safety risk re an overrun existed.


If you want a simplistic answer for IRSE exam then I suggest best to default to use option d), but if the layout is definitely indicating that there are specific shunt overlaps then use option c)

Also another question, I did not find much about the approach locking in Study Pack. So I checked the British Rail Control Table.
It is said "Shunt signal only become approach locked once a proceed aspect has been displayed and any berth track within 50 yards has been occupied. In the absence of a berth track, the sigala is approach locked when cleared."

So is it only in a shunt route, approach locked applies for signal when signal clear or TC occ?
And does it require the berth track shorter than 50yard (45m)? There is only one case in that book, so I can hardly judge my reference is right or wrong.
I refer to the column in CT as attached.

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).
Hence if there is a berth track which is at least 45m long, then this is the one track which is listed; in the odd case that the first track is less than this then would need to include the second track back as well. If the only track is less than 45m or there is no berth TC at all, then comprehensive cannot be provided, so no tracks are listed and th entry is "when cleared"