St. Andrews signalling questions

At Crowcombe Heathfield (WSR) the section signal is the last signal that the driver sees before he gets to the home signal of either Williton SB or Bishops Lydeard SB.

AFAIK SA47 is only a “backing” signal - if you could set route SA7 - SA47 - SA37 (and they’re on two different panels in St Andrews box so I’m not sure you can), SA7 will never clear - it’s provided so a train can come down the Beach branch and reverse behind SA47 to head towards Hallen Marsh

The ‘One Train Working’ single line section for trains operating along the Main Line between St. Andrews Junction and Severn Beach commences beyond 138A points at Holesmouth Junction. Signals SA47 and SA45 are the ‘protecting signals’ for the purposes of Rule Book, Module TW1, Section 32 instructions.It will be possible to signal trains between the Down and Up Avonmouth Dock Lines and Hallen Marsh Junction or the Avonmouth PBA sidings with a train already occupying the single line section to Severn Beach.

You need to look at the diagrams that Geoff has provided. They will be authoritative.

SA7 doesn't have a yellow aspect. Therefore the green can't be providing information about the state of SA47. I don't know if there's a repeater or fixed distant or whether drivers are just supposed to know about this. But see below.

SA47 *has* to be able to show red because it protects a junction. There is no way that an arrangement that has it showing yellow while the points move would be acceptable. I don't know whether SA7 is held at red until SA47 is cleared - there's no info box in Geoff's extract - though it seems a long distance for this. If SA7 had a yellow there would be too much chance of the driver forgetting the aspect.

The table says that SA47 can't clear with the feather unless SA37 is at least yellow.

If I'm interpreting your quote from the Sectional Appendix correctly, it may well be that SA7 can't clear with SA47 at red. Drivers should still keep any eye open for SA47 being red in case of an emergency or failure.

I would add that the sectional appendix was updated (back in october 2018 if the update date on the section is to belived) to now state:
NR said:

The ‘One Train Working’ single line section for trains operating along the Main Line between St. Andrews Junction and Severn Beach commences beyond 138A points at Holesmouth Junction. Signals SA47 and SA45 are the ‘protecting signals’ for the purposes of Rule Book, Module TW1, Section 32 instructions.It will be possible to signal trains between the Down and Up Avonmouth Dock Lines and Hallen Marsh Junction or the Avonmouth PBA sidings with a train already occupying the single line section to Severn Beach.

So I would imagine that something (though I have no knowledge of what) has possibly changed with how this junction is worked since slugsix read their older copy of the sectional appendix. (which may (though I don't think it is too likely) mean that SA7 could now have a yellow and geoff's diagrams may possibly be put of date.)

Indeed. Several modifications were made recently, although I'm not particularly interested in them, because it's not the period I'm interested in. For example, modifications were made in the Clifton area that allows trains to be routed into either platform from Redland.

I've seen a document about all the changes that were made, so maybe it mentions something about St. Andrews which may shed some more light on it.....

Tempest Malice in post 128783 said:

I would add that the sectional appendix was updated (back in october 2018 if the update date on the section is to belived) to now state:
NR said:

The ‘One Train Working’ single line section for trains operating along the Main Line between St. Andrews Junction and Severn Beach commences beyond 138A points at Holesmouth Junction. Signals SA47 and SA45 are the ‘protecting signals’ for the purposes of Rule Book, Module TW1, Section 32 instructions.It will be possible to signal trains between the Down and Up Avonmouth Dock Lines and Hallen Marsh Junction or the Avonmouth PBA sidings with a train already occupying the single line section to Severn Beach.

So I would imagine that something (though I have no knowledge of what) has possibly changed with how this junction is worked since slugsix read their older copy of the sectional appendix. (which may (though I don't think it is too likely) mean that SA7 could now have a yellow and geoff's diagrams may possibly be put of date.)

I have been thinking it through, and I have a few thoughts here. This is all speculation, so take with a pinch of Sodium Chloride.

Firstly, A 3 aspect signal head dosen't mean that the signal can display all three aspects. Given that the rest of the St Andrews area is all three aspect, its possible that they used another three aspect head on a two aspect signal to cut down on costs.

Secondly (And this is the long bit), Having two panels in the box, to me suggests that something is at play here. Before the BHT opened, you had St Andrews OCS Panel which just controlled the loops at Avonmouth, and the single line towards Severn Beach. At the time, it is my understanding that this was token worked, and that a token would be needed to access the BP terminal or the siding at Severn Beach.

Based on this, I suspect that the new panel which was added for the BHT in St Andrews Panel was done such that it was all installed in the former token section, therefore requiring as little modifications to the existing setup as possible (Feeding some track indications back, or removing the token system, that kind of idea).

If SA7 was to be made a three aspect signal, so it could read Yellow onto SA47, I would assume that this would have added extra expense for very little benefit. Most likely, they never considered the possibility of trains doing anything other than Avonmouth to Severn beach along that stretch. Possibly with the signalled route being added as an afterthought.

In relation to SA47, after having written some midland sims, and considering the slotting arrangement from Wigan Wallgate to Warrington PSB, (Please see image in this post https://www.SimSig.co.uk/Forum/ThreadView/50882?postId=128404), that SA47 almost acts like a route setting slot, all be it, capable of showing an aspect.

Finally, that file you have liked to is all proposals. There is nothing I've seen to suggest that anything on the Avonmouth to Severn Beach area has been changed in any way

James

SA7 is still only capable of showing Red and Green aspects to this day

You are incorrect to suggest that the rest of St. Andrews was all 3 aspect. It was not.

SA2R - 2A Y/G
SA2 - 2A ?/?
SA3R - 2A Y/G
SA3 - 2A R/Y
SA4 - Could be 2 aspect, difficult to tell from Cab ride
SA8 - 2A R/G
SA38 - 2A R/G
SA47 - 2A R/G

To list just those I know of.

James

No, you’re overthinking it

SA47 can show Red, correct, and is the nominated signal as far as the OTW rules are concerned.

But none of that means that SA47 is approachable at Red. The prior interlocking of 7 requiring 47 off still applies, and hasn’t been changed in about 30 years since the new panel was put in for Avonmouth BHT.

It looks to have changed wording around the same time as the rail connection into the Severnside waste terminal was commissioned - as the rail connection is within the OTW section as a GF with lock in capabilities, perhaps it was changed to allow a train to enter the OTW section via a reversal at SA47 - otherwise technically would it not always have to route via Clifton?