Help with a signalling question please.

[Bogallan]

Reproduced from Hornby Hobbies “The Collector” magazine recently there is a picture of a train near Durham. Nothing special in that, however, the engine has just passed under a semaphore signal with home and distant arms and between them is what looks like a subsidiary or calling on arm. All the signals appear to be in the “off” position.
i have not seen such a signal before and so I am questioning what was the meaning of the subsidiary signal when the driver would have taken the main line signals as his authority to proceed?

 

[Master29]

I think it's called a subsidiary signal and was used in relation to shunting to and from the yards from the mainline.

 

[jfollows]

I think it's called a subsidiary signal and was used in relation to shunting to and from the yards from the mainline.

Yes, but why is it off then is - I think - the question? You can’t go main line and into the yard at the same time!

 

[Master29]

Yes, but why is it off then is - I think - the question? You can’t go main line and into the yard at the same time!

Isn't there three possible letters that allow for three different scenarios when the signal is in the off position? A calling on signal, shunt signal and warning signal shown with C,S and W respectively. We cannot see which letter is being displayed however which might explain the confusion.

 

[zwk500]

I think it's called a subsidiary signal and was used in relation to shunting to and from the yards from the mainline.

Could also be used for movements in and around the station (e.g. to allow a portion to be shunted onto the rear of the platform). If that picture is of Durham Viaduct that is presumably the down signal gantry and it being the taller post indicates the moves are set for the through road.

Yes, but why is it off then is - I think - the question? You can’t go main line and into the yard at the same time!

At a guess - the Subsidiary arm is pulled off with the main to avoid potential confusion of 1 red and 1 green light at night.

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Isn't there three possible letters that allow for three different scenarios? A calling on signal, shunt signal and warning signal shown with C,S and W respectively. We cannot see which letter is being displayed however which might explain the confusion.

Was use of the letter universal? There are the backs of three much shorter signals indicating sidings/loops turning out to the right on that gantry, so I'd imagine that the Subsidiary arms on the Through and Loop posts are more for Calling on moves than signalling yard access.

 

[12LDA28C]

Yes, but why is it off then is - I think - the question? You can’t go main line and into the yard at the same time!

Indeed. It also appears that the distant is also off which would seem to indicate that the train is continuing along the mainline for at least the next signal section which still wouldn't explain why the subsidiary was also 'off'.

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At a guess - the Subsidiary arm is pulled off with the main to avoid potential confusion of 1 red and 1 green light at night.

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There shouldn't be any confusion - the driver's route knowledge should see to that, and presumably a train would be checked down to (or almost to) a stand at the main semaphore arm before the subsidiary would be pulled off for the shunt / calling on movement or whatever. You don't see a proceed colour light signal with a position light also illuminated beneath, which would be a more modern example of the same sort of thing.

 

[edwin_m]

There's a 1950 signalling diagram linked here which shows the small arms, and there are others approaching from the north.

Track Diagram: <? print $boxname . " (" . $plandate . ")" ?>

My guess is it's a calling-on signal, which would be cleared on its own if the train was to enter an occupied platform or through track. There is no other shunting route possible from these signals (any move into sidings to the north would be signalled through to the North box where an appropriate shunting arm would be used). So it's logical, but unusual, that if a train is signalled straight through, the calling-on arm would also clear.

 

[zwk500]

You don't see a proceed colour light signal with a position light also illuminated beneath, which would be a more modern example of the same sort of thing.

The PL indication not being illuminated is a development of the concept of clearing both at the same time - for obvious reasons you can't make a semaphore arm invisible until it's needed.

 

[Master29]

Indeed. It also appears that the distant is also off which would seem to indicate that the train is continuing along the mainline for at least the next signal section which still wouldn't explain why the subsidiary was also 'off'.

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There shouldn't be any confusion - the driver's route knowledge should see to that, and presumably a train would be checked down to (or almost to) a stand at the main semaphore arm before the subsidiary would be pulled off for the shunt / calling on movement or whatever.

I think you've answered your own point as to why it wouldn't explain the signal in the off position in your reply to zwk500 where drivers route knowledge would suffice. He would know about the 3 letters that can be shown I mention in my reply to post 4

 

[12LDA28C]

The PL indication not being illuminated is a development of the concept of clearing both at the same time - for obvious reasons you can't make a semaphore arm invisible until it's needed.

Of course, but I believe my point still stands about being brought to, or almost to a stand (sufficiently close to be able to see both signals clearly) before the calling on semaphore would clear.

 

[zwk500]

There's a 1950 signalling diagram linked here which shows the small arms, and there are others approaching from the north.

Track Diagram: <? print $boxname . " (" . $plandate . ")" ?>

Thanks for this - interestingly both Signals show the Main and Calling-on arms as the same lever number but with a little 1 and 2 next to them. Assuming this means both are moved by the same lever, and no slotting is shown for the main aspect, does anybody know how the interlocking would know not to lift the main aspect when able? Would it be linked to the Block instrument?

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Of course, but I believe my point still stands about being brought to, or almost to a stand (sufficiently close to be able to see both signals clearly) before the calling on semaphore would clear.

It does, but then there are many examples of interlocking practices going above and beyond what driver knowledge should do. The Signal diagram linked by @edwin_m however suggests that simply space in the frame may also have been a motivating factor for this arrangement - both Sub and Main are driven off the same lever.

 

[507 001]

Thanks for this - interestingly both Signals show the Main and Calling-on arms as the same lever number but with a little 1 and 2 next to them. Assuming this means both are moved by the same lever, and no slotting is shown for the main aspect, does anybody know how the interlocking would know not to lift the main aspect when able? Would it be linked to the Block instrument?

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It does, but then there are many examples of interlocking practices going above and beyond what driver knowledge should do. The Signal diagram linked by @edwin_m however suggests that simply space in the frame may also have been a motivating factor for this arrangement - both Sub and Main are driven off the same lever.

Depression bar?

 

[zwk500]

Depression bar?

Is that what's indicated by Levers 12 and 29 in the diagram? Sorry I don't know much about that technology. I guess it could have also had track circuits.

 

[edwin_m]

Here's the corresponding diagram for Durham North if it helps: https://signalbox.org/~SBdiagram.php?id= 830

For the main signal to clear, the track would have to be unoccupied at least as far as the next main signal and probably beyond, depending on how "clearing points" worked in this area. A depression bar only proves the track clear within its own length, so this situation would need a track circuit (or, in more recent times, an axle counter) and I somehow doubt the state of a track circuit would lead to a different arm being cleared in that era.

I'm wondering if the main arm would only clear if Durham North had pulled its distant off, possibly due to no clearing point beyond the north end of the platforms. This might also explain the subsidiary arm clearing with the main arm - if it didn't then the subsidiary would have to drop back to danger when North cleared its distant and allowed the main stop arm to clear, which might be difficult to arrange in a slotting mechanism and/or confusing to drivers. But as @zwk500 has mentioned above, there is no indication of any slotting on the main stop arms.

Edit: I've also read somewhere that you would occasionally find three-position levers, and thinking some more I think that may be the answer and what the little 1 and 2 are seeking to convey. Pulling the lever to its first detent would require the locking conditions for the subsidiary route and clear only the subsidiary arm, but pulling it to position 2 would also require additional locking conditions if any, possibly the block instrument from North, or the signalman was trusted not to pull it to this position unless the platform was clear and North had given an unrestricted acceptance through to the clearing point beyond the station. Again, if the subsidiary arm cleared only in position 1, then pulling the lever all the way to position 2 would cause it to clear and immediately drop back, which doesn't seem like good practice and would explain why it would remain clear in position 2.

 

[John Webb]

....Edit: I've also read somewhere that you would occasionally find three-position levers, and thinking some more I think that may be the answer and what the little 1 and 2 are seeking to convey. Pulling the lever to its first detent would require the locking conditions for the subsidiary route and clear only the subsidiary arm, but pulling it to position 2 would also require additional locking conditions if any, possibly the block instrument from North, or the signalman was trusted not to pull it to this position unless the platform was clear and North had given an unrestricted acceptance through to the clearing point beyond the station. Again, if the subsidiary arm cleared only in position 1, then pulling the lever all the way to position 2 would cause it to clear and immediately drop back, which doesn't seem like good practice and would explain why it would remain clear in position 2.

I'm fairly certain that this interpretation is correct - three-position levers which clear the calling-on signal first, and then the main arm when fully reversed in the frame. Regarding calling-on arms, they could be marked with a C or other letter, or when pulled 'off' might reveal the appropriate letter previously hidden by the horizontal arm. The calling-on arms were also usually coloured red with a horizontal white stripe to distinguish them from the main signals. The John Hinson diagram linked to by edwin_m would have shown the appropriate letter if they'd been anything else but calling-on arms, I understand.

 

[Tomnick]

It was NER (and apparently Midland too) practice for the interlocking to require the calling-on arm to be cleared before the main arm was able to be cleared, so you'd have both off for a move to an unoccupied line as you see here. Other companies only cleared the calling-on arm if it was a move to an occupied line (so you'd never see both off together), which is the practice that persisted to today of course.

 

[LYRobert]

I have sometimes seen a calling-on disc pulled 'off', and recently (dunno where) two white lights diagonally, when the train I'm on is routed into a platform somewhere or other (might have been New Street). I don't think it is uncommon. It is probably done by the interlocking. OK, imagine I'm coming into platform 2 but Hey, what's this? On the left at ground level there's a red-with-white! What do I do? Better that it clears to two white lights diagonally so that there's no reds in the view, and thus no confusion created.

 

[Sheridan]

I have sometimes seen a calling-on disc pulled 'off', and recently (dunno where) two white lights diagonally, when the train I'm on is routed into a platform somewhere or other (might have been New Street). I don't think it is uncommon. It is probably done by the interlocking. OK, imagine I'm coming into platform 2 but Hey, what's this? On the left at ground level there's a red-with-white! What do I do? Better that it clears to two white lights diagonally so that there's no reds in the view, and thus no confusion created.

It’s certainly normal practice that if a route is set between two main signals then any ground signals between them will also be cleared unless this isn’t possible for some reason. It’s a bit different when the subsidiary signals are located on the same post.

 

[Rescars]

It was NER (and apparently Midland too) practice for the interlocking to require the calling-on arm to be cleared before the main arm was able to be cleared, so you'd have both off for a move to an unoccupied line as you see here. Other companies only cleared the calling-on arm if it was a move to an occupied line (so you'd never see both off together), which is the practice that persisted to today of course.

This does seem like the most likely explanation. That said, does the fact that the train in question appears to be a livestock working have any bearing on which signals would be cleared (to avoid heavy braking perhaps)?

 

[Napier]

View attachment 140340

Reproduced from Hornby Hobbies “The Collector” magazine recently there is a picture of a train near Durham. Nothing special in that, however, the engine has just passed under a semaphore signal with home and distant arms and between them is what looks like a subsidiary or calling on arm. All the signals appear to be in the “off” position.
i have not seen such a signal before and so I am questioning what was the meaning of the subsidiary signal when the driver would have taken the main line signals as his authority to proceed?

Might be some info on here.

LNER Signal Box Diagrams

== Doublepost prevention - post automatically merged: 6 Aug 2023 ==

 

[12LDA28C]

Might be some info on here.

LNER Signal Box Diagrams

== Doublepost prevention - post automatically merged: 6 Aug 2023 ==

View attachment 140482

The meaning of a calling-on signal is well understood. The question in this thread was why was the calling-on signal 'off' when the main aspect to which it relates was also 'off', but that seems to have been answered now in post #16.

 

[30907]

Totally OT: can anyone identify the location "near Durham"? It's not Durham Viaduct (nor I think Newcastle/Gateshead).

 

[stuving]

Totally OT: can anyone identify the location "near Durham"? It's not Durham Viaduct (nor I think Newcastle/Gateshead).

It is Durham viaduct - seen from the battery in Wharton Park with a pretty long lens, and with the workhouse right behind the signal gantry.

 

[Napier]

Totally OT: can anyone identify the location "near Durham"? It's not Durham Viaduct (nor I think Newcastle/Gateshead).

Definitely taken from Wharton Park my old man used to take me there as a kid.

 

[Mugby]

The train is clearly on the track closest to the edge of the viaduct, so what are the signals on the extreme right (all 'On') for?

 

[edwin_m]

The train is clearly on the track closest to the edge of the viaduct, so what are the signals on the extreme right (all 'On') for?

There are only two tracks on the viaduct - the loops start immediately to the north. Looking at the signalling diagram I linked above, the multiple small arms are for trains to shunt back from the Up line on the viaduct (the further one) into the Up or Down lines through the station or various sidings on the east side. A train can't approach these signals from the south, only by coming from the station and reversing on the viaduct.

 

[Tomnick]

This does seem like the most likely explanation. That said, does the fact that the train in question appears to be a livestock working have any bearing on which signals would be cleared (to avoid heavy braking perhaps)?

No – if the line's unoccupied (which would be the case for the vast majority of trains here), then you'd get the main arm regardless.

The train is clearly on the track closest to the edge of the viaduct, so what are the signals on the extreme right (all 'On') for?

If you mean those on the right-hand side as viewed by the photographer, then they're applicable to the same line, but for the diverging route into the Down Slow. They're spaced rather more widely than you might expect, because that route used to have a (rather extravagant, in this case?!) splitting distant, presumably for the route back out onto the Fast beyond the station, which would've been on a doll between the two remaining ones.

 

[Rescars]

With reference to edwin_m's track diagram, a couple of other questions relating to the distant signals leading up to the gantry in the photograph. Can anyone explain the meaning of the unnumbered distant superimposed on a cleared stop signal shown below signal 52? Also, further out, there is another distant "underbolted from Durham North". Is this NER terminology for the same thing as "slotted" used elsewhere (requiring a pull from both Durham South and Durham North for the signal to clear), or does it mean something different? All clarification welcome!

 

[Railsigns]

With reference to edwin_m's track diagram, a couple of other questions relating to the distant signals leading up to the gantry in the photograph. Can anyone explain the meaning of the unnumbered distant superimposed on a cleared stop signal shown below signal 52?

The symbol that looks like a cleared stop signal represents a slot. On this particular diagram, the slotting of a distant arm by the stop arm above it is implicit, and no symbol is shown. The symbol here indicates that the distant arm is additionally backslotted by the next stop signal beyond.

Also, further out, there is another distant "underbolted from Durham North". Is this NER terminology for the same thing as "slotted" used elsewhere (requiring a pull from both Durham South and Durham North for the signal to clear), or does it mean something different? All clarification welcome!

An underbolt is a form of mechanical release on a lever, as distinct from a slot which is on the signal.

 

[30907]

It is Durham viaduct - seen from the battery in Wharton Park with a pretty long lens, and with the workhouse right behind the signal gantry.

OK I stand corrected. I was puzzled because the track appears to curve the wrong way - ie the photographer is on the outside of the curve whereas Wharton Park is on the inside. Wide angle distortion?