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St. Andrews signalling questions

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St. Andrews signalling questions 02/07/2020 at 16:10 #128805
Hap
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JamesN in post 128804 said:
No, the changed wording the the Sectional doesn’t mean SA47 is approachable at Red - and although it would open up that possibility in future, you don’t gain anything service-wise by permitting it with the current track layout.

Both SA2 and SA4 are 3 aspect. I have drawings, but no way of uploading them from work
You should be working. *shakes head*

HAP
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St. Andrews signalling questions 02/07/2020 at 16:21 #128807
JamesN
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Hap in post 128805 said:
JamesN in post 128804 said:
No, the changed wording the the Sectional doesn’t mean SA47 is approachable at Red - and although it would open up that possibility in future, you don’t gain anything service-wise by permitting it with the current track layout.

Both SA2 and SA4 are 3 aspect. I have drawings, but no way of uploading them from work
You should be working. *shakes head*
Hark who’s talking =P

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St. Andrews signalling questions 02/07/2020 at 18:14 #128812
GeoffM
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Lots of comments so I might be repeating what others have said.

The extracts I posted were from the locking diagrams. As Clive says, these are pretty authoritative. In 20 years of poring many hundreds over such diagrams, I've only been aware of mistakes in signed-off versions maybe a handful of times. The latest sign-off date on these are 2004 (Holesmouth) and 2005 (Avonmouth station). These are about the time of the Filton works.

The document you linked to is a proposal and you'll notice a lack of signatures on various pages: such diagrams should be considered non-authoritative. GRIP2 is quite early in the process as well. That said, the comments about the OTW are interesting which suggests a bit of a (safe) "bodge" to modify the interlocking at some point.

SA2 and SA4 are 3 aspect R/Y/G. I could post pictures but the plans are very long with a lot of white space.

Whether SA47 can be approached at red, I don't know. I wouldn't have thought so given the linespeed, plus, as you say, it is mentioned in that document you linked to. SA47 is not approach controlled for either route. It wasn't me that said SA47's red aspect is for reversals, but it's a junction so it needs a red aspect. SA7 would not need to be off to get SA47 off. It's possible the now-gone SA9 signal James mentioned is the cause of this confusion: it wouldn't be the first time something is overly restrictive (SA47 being off for SA7 to be off) to avoid modifying an interlocking too much (see my earlier bodge comment).

Going back, a 1988 signalling notice shows 2/4/6 as capable of R/Y/G, while 2 and 9 (the latter outside the signalbox) as R/G, with 7 capable of Y/G. It doesn't show signal information around Holesmouth, though interestingly the oil terminal simply crossed the Severn Beach line with no connection, via a ground frame.

SimSig Boss
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St. Andrews signalling questions 02/07/2020 at 18:40 #128813
TUT
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GeoffM in post 128812 said:
Whether SA47 can be approached at red, I don't know. I wouldn't have thought so given the linespeed, plus, as you say, it is mentioned in that document you linked to. SA47 is not approach controlled for either route. It wasn't me that said SA47's red aspect is for reversals, but it's a junction so it needs a red aspect. SA7 would not need to be off to get SA47 off. It's possible the now-gone SA9 signal James mentioned is the cause of this confusion: it wouldn't be the first time something is overly restrictive (SA47 being off for SA7 to be off) to avoid modifying an interlocking too much (see my earlier bodge comment).

Going back, a 1988 signalling notice shows 2/4/6 as capable of R/Y/G, while 2 and 9 (the latter outside the signalbox) as R/G, with 7 capable of Y/G. It doesn't show signal information around Holesmouth, though interestingly the oil terminal simply crossed the Severn Beach line with no connection, via a ground frame.
The relevant signalling notice from 1994 concerning closure of Henbury West confirms that at that time:

Quote:
Signal SA.7 will be altered to show a Red or Green aspect only and will only show a green aspect when signal SA.47 also shows a green aspect
(Available to SRS members from: https://www.s-r-s.org.uk/ArchiveSignals/rtwr.php It's right at the top of the list)

The only very slight wrinkle is that at the time of that notice SA47 has just one route so it's evident further work was done at a later time. I very very much doubt that work would have allowed SA7 to to come off with SA47 on, though.

Last edited: 02/07/2020 at 18:41 by TUT
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St. Andrews signalling questions 02/07/2020 at 19:04 #128815
slugsix
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Thanks guys, that's all making sense now. Thanks also for the info on SA2 and SA4 being 3CL R/Y/G.

SA47 has had a feather on it since at least 2005, and there have been a number of diversions (and engineers trains), that have used the diverging route from it.

The inbound binliner reverses in the area does anybody know the move. Does it reverse at SA47 (which it seems it could do), or does it go all the way back to beyond SA7 to reverse?

If you look at the schedule (like todays for example), it looks a little convoluted, with three reverses shown. Not sure if it actually uses all of these - the diversions could access Avonmouth directly from the Hallen lines. I may have to go and have a look one day. It's often TnT I notice, so that may help....

Link to todays schedule, which will expire in a few days for interest:

https://www.realtimetrains.co.uk/train/H06052/2020-07-02/detailed

Last edited: 02/07/2020 at 19:11 by slugsix
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St. Andrews signalling questions 02/07/2020 at 19:23 #128817
JamesN
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Today it reversed behind SA47
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St. Andrews signalling questions 02/07/2020 at 19:35 #128818
GeoffM
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slugsix in post 128815 said:
The inbound binliner reverses in the area does anybody know the move. Does it reverse at SA47 (which it seems it could do), or does it go all the way back to beyond SA7 to reverse?

If you look at the schedule (like todays for example), it looks a little convoluted, with three reverses shown. Not sure if it actually uses all of these - the diversions could access Avonmouth directly from the Hallen lines. I may have to go and have a look one day. It's often TnT I notice, so that may help....

Link to todays schedule, which will expire in a few days for interest:

https://www.realtimetrains.co.uk/train/H06052/2020-07-02/detailed
https://www.opentraintimes.com/schedule/H06052/2020-07-02

I prefer OTT over RTT because the former is more pure, whereas RTT tend to "fill in" information it thinks should be there and is not always helpful.

Anyway, that shows the train coming in from Filton, running around opposite St Andrews Road station, heading back to Hallen Marsh where it reverses, and thence to St Andrews Road to reverse again in order to access the Severn Beach branch. I doubt it would go to SA7: it's unusual to be able to reverse direction on a single line with two or more signals because of directional locking.

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St. Andrews signalling questions 02/07/2020 at 19:38 #128819
slugsix
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The return schedule tonight shows it reversing at Avonmouth!

https://www.realtimetrains.co.uk/train/H05908/2020-07-02/detailed

Does anybody actually know what the driver was for changing the wording in the Sectional Appendix and shortening the OTW section from SA7 to SA47 (138A points)?

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St. Andrews signalling questions 02/07/2020 at 19:41 #128820
slugsix
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Depends what you want out of it I suppose. OTT may be more "pure", but RTT is a lot more user friendly. Horses for courses. I only ever use either as an "overview". I normally prefer the signalling diagrams....

GeoffM in post 128818 said:
slugsix in post 128815 said:
The inbound binliner reverses in the area does anybody know the move. Does it reverse at SA47 (which it seems it could do), or does it go all the way back to beyond SA7 to reverse?

If you look at the schedule (like todays for example), it looks a little convoluted, with three reverses shown. Not sure if it actually uses all of these - the diversions could access Avonmouth directly from the Hallen lines. I may have to go and have a look one day. It's often TnT I notice, so that may help....

Link to todays schedule, which will expire in a few days for interest:

https://www.realtimetrains.co.uk/train/H06052/2020-07-02/detailed
https://www.opentraintimes.com/schedule/H06052/2020-07-02

I prefer OTT over RTT because the former is more pure, whereas RTT tend to "fill in" information it thinks should be there and is not always helpful.

Anyway, that shows the train coming in from Filton, running around opposite St Andrews Road station, heading back to Hallen Marsh where it reverses, and thence to St Andrews Road to reverse again in order to access the Severn Beach branch. I doubt it would go to SA7: it's unusual to be able to reverse direction on a single line with two or more signals because of directional locking.

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St. Andrews signalling questions 02/07/2020 at 19:55 #128821
slugsix
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Apparently it reversed at SA47 today - on the single line. I'm guessing it didn't need the tripple shuffle as it was TnT and therefore did not need to run around. Presume it was therefore just routed from SA28 to SA30 to just beyond SA47 and then back to Severnside SITA.

GeoffM in post 128818 said:


Anyway, that shows the train coming in from Filton, running around opposite St Andrews Road station, heading back to Hallen Marsh where it reverses, and thence to St Andrews Road to reverse again in order to access the Severn Beach branch. I doubt it would go to SA7: it's unusual to be able to reverse direction on a single line with two or more signals because of directional locking.

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St. Andrews signalling questions 02/07/2020 at 21:12 #128832
Stephen Fulcher
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I suspect the reason for a three aspect head on SA7 is simply that when SA9 was removed there was no economic value in replacing the signal head so the lamp would simply have been removed from the yellow aspect and the interlocking adjusted so that it could never be called.

Interestingly before the sectional appendix was adjusted to amend the section to be Points SA138A rather than the more restrictive SA7 signal, the interlocking would have allowed a lot of moves that would have technically broken the OTW regulations (although not been unsafe I should add).

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St. Andrews signalling questions 02/07/2020 at 21:35 #128833
GeoffM
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Stephen Fulcher in post 128832 said:
I suspect the reason for a three aspect head on SA7 is simply that when SA9 was removed there was no economic value in replacing the signal head so the lamp would simply have been removed from the yellow aspect and the interlocking adjusted so that it could never be called.
Previously it was Y/G only.

SimSig Boss
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St. Andrews signalling questions 03/07/2020 at 09:42 #128851
slugsix
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That's interesting. That would mean that SAR LC was unprotected by SA7. Was SA5 still R/Y when SA7 was Y/G then? Or was SA5 different too? That's another anomaly.

This whole area seems to be a pile of bodges - to do stuff on a shoestring no doubt. But over time, IMO, it ends up costing you far more. They will have to sort out Holesmouth Junction properly at some point, it's a shame they didn't do it properly when the BBHT was put in.

Still no authoratative answer on why the wording in the SA was changed?

GeoffM in post 128833 said:
Stephen Fulcher in post 128832 said:
I suspect the reason for a three aspect head on SA7 is simply that when SA9 was removed there was no economic value in replacing the signal head so the lamp would simply have been removed from the yellow aspect and the interlocking adjusted so that it could never be called.
Previously it was Y/G only.

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St. Andrews signalling questions 03/07/2020 at 09:54 #128854
kbarber
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Of course there is a requirement that the first set of points in a route is no more than... (I *think* it's 800m?) from the protecting signal. Maybe that was the driver for providing 47 signal in the first place?
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St. Andrews signalling questions 03/07/2020 at 10:00 #128855
slugsix
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Out of interest, is SA38 a 3 aspect or 2 aspect. The following signal is SA2R Y/G, which suggests SA38 only needs to be 2 aspect R/G.....

(From the cab ride, it looks like 2A but it's really hard to tell and I'm not sure!)

Last edited: 03/07/2020 at 10:02 by slugsix
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St. Andrews signalling questions 03/07/2020 at 11:10 #128861
Stephen Fulcher
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We would probably need to see the complete scheme plans and control tables from before the BHT was installed to answer a lot of these.
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St. Andrews signalling questions 08/07/2020 at 19:22 #129301
slugsix
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Another "unusual" thing I noticed is that the AWS magnets for SA4 and SA7 are co-located.
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St. Andrews signalling questions 08/07/2020 at 19:33 #129303
GeoffM
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slugsix in post 128855 said:
Out of interest, is SA38 a 3 aspect or 2 aspect. The following signal is SA2R Y/G, which suggests SA38 only needs to be 2 aspect R/G.....

(From the cab ride, it looks like 2A but it's really hard to tell and I'm not sure!)
SA38 is a 2-aspect R/G

slugsix in post 129301 said:
Another "unusual" thing I noticed is that the AWS magnets for SA4 and SA7 are co-located.
This is actually very common.

SimSig Boss
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St. Andrews signalling questions 08/07/2020 at 20:20 #129309
slugsix
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GeoffM in post 129303 said:
slugsix in post 128855 said:
Out of interest, is SA38 a 3 aspect or 2 aspect. The following signal is SA2R Y/G, which suggests SA38 only needs to be 2 aspect R/G.....

(From the cab ride, it looks like 2A but it's really hard to tell and I'm not sure!)
SA38 is a 2-aspect R/G

slugsix in post 129301 said:
Another "unusual" thing I noticed is that the AWS magnets for SA4 and SA7 are co-located.
This is actually very common.
Thanks Geoff. Appreciate the help. Whilst you may be able to quote a number of co-located AWS magnets at me, it is by no means the norm, and it's the first one I've come across in the Bristol area. Not the norm = not the usual = unusual.

Thanks again for the help.

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St. Andrews signalling questions 08/07/2020 at 20:31 #129310
GeoffM
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slugsix in post 129309 said:
GeoffM in post 129303 said:
slugsix in post 128855 said:
Out of interest, is SA38 a 3 aspect or 2 aspect. The following signal is SA2R Y/G, which suggests SA38 only needs to be 2 aspect R/G.....

(From the cab ride, it looks like 2A but it's really hard to tell and I'm not sure!)
SA38 is a 2-aspect R/G

slugsix in post 129301 said:
Another "unusual" thing I noticed is that the AWS magnets for SA4 and SA7 are co-located.
This is actually very common.
Thanks Geoff. Appreciate the help. Whilst you may be able to quote a number of co-located AWS magnets at me, it is by no means the norm, and it's the first one I've come across in the Bristol area. Not the norm = not the usual = unusual.
Examples can be found at:
Bedminster
North Somerset Jn
Filton Abbey Wood
Westerleigh Jn
Weston-super-Mare
Bristol Parkway
...to name a few. So yeah, quite normal on bi-directional lines.

SimSig Boss
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St. Andrews signalling questions 08/07/2020 at 20:40 #129311
Stephen Fulcher
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Anywhere there is a main signal at either end of a platform you’ll often find this arrangement
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St. Andrews signalling questions 08/07/2020 at 20:40 #129312
JamesN
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GeoffM in post 129310 said:
slugsix in post 129309 said:
GeoffM in post 129303 said:
slugsix in post 128855 said:
Out of interest, is SA38 a 3 aspect or 2 aspect. The following signal is SA2R Y/G, which suggests SA38 only needs to be 2 aspect R/G.....

(From the cab ride, it looks like 2A but it's really hard to tell and I'm not sure!)
SA38 is a 2-aspect R/G

slugsix in post 129301 said:
Another "unusual" thing I noticed is that the AWS magnets for SA4 and SA7 are co-located.
This is actually very common.
Thanks Geoff. Appreciate the help. Whilst you may be able to quote a number of co-located AWS magnets at me, it is by no means the norm, and it's the first one I've come across in the Bristol area. Not the norm = not the usual = unusual.
Examples can be found at:
Bedminster
North Somerset Jn
Filton Abbey Wood
Westerleigh Jn
Weston-super-Mare
Bristol Parkway
...to name a few. So yeah, quite normal on bi-directional lines.
It’s actually easier to co-locate them on BiDi lines than have them separate - less suppression circuitry and the like involved.

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St. Andrews signalling questions 09/07/2020 at 10:49 #129358
clive
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JamesN in post 129312 said:

It’s actually easier to co-locate them on BiDi lines than have them separate - less suppression circuitry and the like involved.
Indeed: no suppression circuitry required.

Co-located: you have one fixed magnet and two electromagnets. Each electromagnet is driven from the DR circuit of the associated signal, just as with normal signalling. Provided it's not possible to clear both signals at the same time, no special logic is required.

Separate: you have two fixed magnets and two electromagnets. Each fixed magnet needs a suppression coil that needs to be driven from (I think) the sub-route locking relay of the appropriate track circuit, which means extra circuitry down to the ground as well as the normal DR drive to the electromagnet.

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St. Andrews signalling questions 09/07/2020 at 12:42 #129362
Stephen Fulcher
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Suppression is normally route locking in the opposite direction to the AWS and the track section occupied.
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