Signalling Questions

[Sunset route]

There is data in the national timetable database for when a particular terminating train is supposed to form the next outgoing service from the same platform under a different headcode. In some cases this information is visible online through Realtime Trains. Automatic route setting (ARS) uses that data routinely to change the headcodes automatically. Some more modern train describers also do this at boxes where there's no ARS. The process can be upset fairly easily however if sets stray from their planned diagrams due to late running or failure and when other spare sets are substituted for the departure from a different platform. I think the ARS and TD systems are intelligent enough to not try and implement a planned automatic substitution where the new headcode has already been used (i.e set up manually elsewhere by the signaller) but I believe there remain some scenarios where the incorrect information can still be interposed automatically under such very short notice real time changes.

It's not ARS that changes the WTT codes but Automatic Code Insertion ACI which the ARS will use for the routing of the next working based on the timetable dada base.

 

[LAX54]

The headcode is now entered by the driver into the GSM-R terminal at login together with the signal berth the train is standing at (or in some cases a special GSM-R location code). This is transferred by GSM-R to the signalling centre and arms the train describer, which then tracks the train as it moves along, as described by others.

Not in our neck of the woods it doesn't There is no way the GSM-R system can enter headcodes into the the TD system.
TD's are either entered by ARS via Auto Hedcode insertion that is based on the WTT, or more commonly the Signaller on the panel.
I am not sure what a 'special GSM-R location code' is, unless you a refering to a 'Signal Berth' ??

 

[MarkyT]

It's not ARS that changes the WTT codes but Automatic Code Insertion ASI which the ARS will use for the routing of the next working based on the timetable dada base.

Ah OK. 'ACI' surely? That's the acronym I couldn't remember, but rather than a standalone 'system' as such surely it's a functional 'feature' of an IECC or TD. I remember in early IECCs signal engineers had to compile hard-coded lists of these insertions as the raw timetable periodically downloaded from the database didn't contain the details. Don't know whether that's the case today, but in that scenario there is a risk that a short term change to the timetable and fleet diagrams may not match up with the separately pre-coded insertion data, hence if the signaller didn't spot a mistake, it was possible a train could get an incorrect code that could contribute towards a misrouting.

 

[Sunset route]

Ah OK. 'ACI' surely? That's the acronym I couldn't remember, but rather than a standalone 'system' as such surely it's a functional 'feature' of an IECC or TD. I remember in early IECCs signal engineers had to compile hard-coded lists of these insertions as the raw timetable periodically downloaded from the database didn't contain the details. Don't know whether that's the case today, but in that scenario there is a risk that a short term change to the timetable and fleet diagrams may not match up with the separately pre-coded insertion data, hence if the signaller didn't spot a mistake, it was possible a train could get an incorrect code that could contribute towards a misrouting.

ACI yes never answer a question fresh after getting in after night shift lol, I'll go back up and correct thanks

 

[QueensCurve]

You are also showing a lack of knowledge on that last wrong route. If you had route knowledge of platform 1 at Crewe. You would know that you depart on a signal with no route indicator. The signal AFTER has the route indicator on it and at that point it is probably too late to stop in time.

INteresting. I didn't know that.

 

[driver_m]

INteresting. I didn't know that.

No, you didn't, but you were quick to point the finger of blame at the driver! Wrong routes are not set up by drivers, blaming the driver is easy to do but that scenario shouldn't have happened in the first place.

 

[ComUtoR]

I am not sure what a 'special GSM-R location code' is, unless you a refering to a 'Signal Berth' ??

99X number ? Alias plate ?

 

[DerekC]

99X number ? Alias plate ?

Alias plate - used at a location where there isn't a signal. The GSM-R location code is cross-referenced to the TD in areas which have "Enhanced Location Dependent Addressing". I am trying to find out where those are. Anybody know?

 

[ComUtoR]

Alias plate - used at a location where there isn't a signal.

I've seen more alias plates on signals than at places without.

 

[DerekC]

I've seen more alias plates on signals than at places without.

According to RSSB they go:

a) When registering at a location where a signal is either not provided
or its number does not correspond to the signal berth.
b) When registering within a cell that has signals where the last three
digits are the same (for example, WC101 and C101).
c) When registering at a signal that has only alpha characters.

 

[ComUtoR]

According to RSSB they go:

a) When registering at a location where a signal is either not provided
or its number does not correspond to the signal berth.

Which means it can be on a signal without a matching berth

b) When registering within a cell that has signals where the last three
digits are the same (for example, WC101 and C101).

On a signal

c) When registering at a signal that has only alpha characters.

On a signal


Not sure if you were trying to prove my point or not.

We have the GSMR plate which basically gives the area code (blue with white lettering)

There is also a GSMR plate instructing the use of a 99X code

And I believe there is one that is similar to the standard alias plate and it instructs the use of a setup code (basically the same as an alias plate) Its white with black lettering. Some also have a telephone number. I've not seen one in use yet but could they be what your after ?

 

[QueensCurve]

No, you didn't, but you were quick to point the finger of blame at the driver! Wrong routes are not set up by drivers, blaming the driver is easy to do but that scenario shouldn't have happened in the first place.

It is not so much a case of blaming the driver, as wondering why the driver colluded with the wrong route.

In the case of Crewe Platform 1 yyou have provided the answer. Still don't know why in the Reading instance when presumably the driver knew services were being diverted via the Berks and Hants.

In a sense the driver has the opportunity (sometimes) to rectify the error but doesn't always.

 

[D Foster]

So I understand many of basic concepts behind signaling such as blocks ect but what I want to know is how is a trains route managed throughout it's journey? How do signallers identify trains and how do they know where to send them? Also how was this done in the age before electronics? And do trains sometimes get sent to incorrect destinations?
.

In the days before "electronics"... Do you mean before "digital"?

If we go back into the early 19th century we arrive at a time before the "Electric Telegraph" and, more relevantly, before the "Electric Block telegraph" - the latter with it's Block Telegraph Instruments and Block Bells - with Bell Codes.

While there are plenty of descriptions of the Time Interval system of working, the early hand signals used by Railway Policemen ("Bobbies") and a few descriptions of early signals there is almost no material in the public domain about train regulation - aka "route setting".

One would have to assume that, along with the dangers of almost no signals and no interlocking the early train crews would approach any junction with caution - looking to see what (if any - hand - signals) might be displayed and exactly how the point blades were set. On the ground the staff probably tried to set up routes according to which train they expected to arrive next - potentially with the aid of a timetable and, possibly more usefully, with local experience. It may also be that Drivers would "blow" for the route they wanted - probably using local codes (combinations of whistle blasts).

Initially the commercial department's electric telegraphs were borrowed by the operating department and used to spell out messages about what trains were about - a very slow and awkward process - compared to the Block Telegraph.

So the Block Telegraph came into use... Using both Block Instruments to indicate line occupation and Block Bells to communicate very short messages - e.g. "Is Line Clear for Stopping Passenger Train?" - "Train entering Section" etc.

Each company and the RCH had lists of standard Block Telegraph Bell Codes. These developed over the years - e.g. to distinguish between electric stock and non-electric stock... Sending a juicer the wrong way could create a problem or two.

There could be additional, specific codes for Branch Line trains and for Terminating services (at through stations).

The Boxes either side of a junction Box could also have specific Bell Codes to "route describe" as well as "Class of train describe". This would usually be from the Box approaching the divergence - although, sometimes, the sides sending through the trailing junction would have different codes in order to assist the junction in distinguishing what was what.

A relevant point is that each set of Block Bells was supposed to both sound different from all the others in the Box and they were also supposed to be placed sufficiently apart (on the Block shelf) to facilitate the signalman recognising the specific bell that had rung. (This is why you often see Block bells of very different shapes).

Which leaves the question... How did the Box before a junction know which way an approaching train would be heading at the junction?
There are stages to this...
A.
1. What train should be approaching "next" at any given time should be in the Working Timetable (WTT).
2.Any variation on the WTT should have been advised before time in a Special Traffic Notice (STN).
3. Failing this (predominantly in an urgent situation) a Special Train Notice could be sent ahead of the movement by a preceding train.
4.Failing these options - there was originally the "Needle Telegraph" (which was what the commercial people used) - and later telephones.

At the "telephone stage" of things changing each Box would (aka "should") phone forward to advise the next Box of an alteration. When possible Boxes called an alteration forward as soon as they knew of it.

To give an example... If a Class 1 or 2 was going to be route diverted for any reason "on the day" the different working would be forwarded - preferably by Special Train Notices - but - if necessary by telephone. This information would be pushed ahead because the changes might mean that lower classes, especially goods trains working yards and hopping between stations/Boxes might need to be held back and/or shunted out of the way.
There was actually a specific Bell Code for "Shunt Train for Following Train to Pass"... Although this would be a pretty last-minute effort and would be avoided whenever possible.

B.
1. Right from early days movements carried headcodes. Before alpha-numeric (mainly 4 digit) headcodes these were either discs or lamps arranged on brackets on the front of locos. These primarily indicated the class of train but could also be used to define route to a limited extent.
2. Some of the more complex "urban" systems (the Metropolitan comes to mind) used destination boards across the buffer beam of the loco. This was a forerunner of destination blinds on MU stock.
3. The Southern in particular used illuminated headcodes with two large numbers. Different pairs of numbers defined different routes. This was on Electric stock first and then on diesels.

From the point of view of the signalmen the disc and lamp headcodes largely confirmed what class the train was. 4 character and 2 number codes were more informative. However; seeing what loco was on the front, and failing that, what was in the train would inform a signalman about where a train was going. Bearing in mind that the system ran on the Mark 1 eyeball for a very long time before anything even approaching "digital" appeared on the scene.

If a Box had belled a train forward and what subsequently came by proved to be something different there was a Bell Code for "Last Train Described Incorrectly Described". After this had been repeated back from the Box In Advance the correct description would be sent.

C.

From a date that I think would be between 1900 and 1910 some of the more complicated junction areas began to be fitted with Train Describers in addition to and then in place of Block Bells.
There were various patterns of train describers - both according to the stage of development and what the railway company wanted to achieve.
Some describers were "rotary" - a bit like a ship's engine room telegraph - with a needle rotating to point to a description. An issue with these was that they only showed one train at a time. This was overcome by using various forms of "magazine describer" - in which a sequence of trains could be described - which would cascade out of the system as each train was worked through... For how all these worked - "Google"!!!
The early describers tended to be more mechanical than electrical with more and more "telephone exchange" kinds of system following as the technology developed.
Eventually descriptions went digital - which kind-of brings us up to the near present.

Did I miss anything?

 

[driver_m]

It is not so much a case of blaming the driver, as wondering why the driver colluded with the wrong route.

In the case of Crewe Platform 1 yyou have provided the answer. Still don't know why in the Reading instance when presumably the driver knew services were being diverted via the Berks and Hants.

In a sense the driver has the opportunity (sometimes) to rectify the error but doesn't always.

'Colluded'? I can't think of an occasion where two railway workers who don't know one another have gone out to deliberately screw up. Or a driver thought, 'sod it, I'll go that way anyway.' That is an awful choice of word. I don't have knowledge of Reading but how do you know that's not a diversionary route that doesn't get questioned? (Route Knowledge again) If I get sent via Northampton I don't question it. However I would at somewhere like Stafford if being sent to Wolves if via the Trent Valley. It could have been autopilot and realised last minute. Ultimately though the buck stops with the person who caused the wrong route in the first place.

 

[najaB]

In the days before "electronics"...

Nice. Thanks for taking the time to post it.

 

[D Foster]

Nice. Thanks for taking the time to post it.

Glad you liked it

A bit more "Old stuff"...

"Pre-digital" when not everything had to be done to the nano-second... * (if not before) not just trains but the whole world moved at a different pace.

Even after loose-coupled, unfitted goods trains stopped being used the operation of vacuum brake and older varieties of air brake impacted on both the speed and timing of trains.
Clearly a loose-coupled, unfitted train and even an Instanta coupled semi-fitted train had to be far more "worked" by the train crew than anything close-coupled and fully automatic braked - although, again, pre EP and later brake systems had to be worked according to the way the brake force was distributed along the train - and - the important thing - how the brakes came back off when released.

All this adds up to the fact that the routeing was a whole different world "pre-digital".
Pre-digital it was not merely a matter of looking at a trains ID and remotely setting a route for it to whiz along. (Far less was there any chance of a computer doing it for you - even where TCB could be left running on auto for periods of time).

So... Putting trains, train crews, routes (points), signals and signalmen together...

Particularly after the Salisbury smash of 1 July 1906 [see Wikipedia "Salisbury rail crash"] the regulating BoT frowned on Splitting Distants and worked Distants approaching severe speed restrictions.
This meant that from then on worked Distants tended to only be provided for diverging routes where both sides of the divergence permitted full Line Speed. (There were, as always, exceptions).
Visually this applied far more obviously to semaphore signals. In many cases the Distant approaching a diverging route would only be a single arm - which would remain "On" except when the route was set and clear through the dominant (faster) route.
The Distant remaining On would slow all approaching traffic down (ready to stop dead on the approach to the first associated (interlocked) Stop Signal... This meant that anything that should be diverging would always be slowed down on the approach to the junction - and therefore able to stop and have the route corrected if the route had been incorrectly set.
Equally, if a train was intended to diverge and a single Distant was Off (for the dominant route) the crew would know that the route was incorrectly set and, again, they could stop in time to have the route reset - or they could pull up to the Box to discover any reason for diversion... Although - if they were being diverted in any unconventional way the signalman should not clear the route through before the train arrived but bring the train to him steadily ("dropping it down on the Box) by clearing the Stop Signals slowly as/when the train was seen to be approaching them ready/able to stop. The train should then be stopped at the Box on a red flag for the crew to be instructed (including drawing the train forward to advise the guard).
Even with only one route provided with a worked Distant errors in route setting could therefore be relatively easily sorted out - both with unfitted, loose coupled goods chugging along at low speed and with fully automatic braked, close-coupled express workings.
(An express expecting a main route and therefore the Distant "Off" would "blow" violently demanding the road if it found the Distant on against it - but it would be brought under control ready to stop at the first Stop Signal).

All this changed somewhat with Colour Light Distants and TCB.

I am realising that I have not previously considered what happened with splitting semaphore Distants when they were replaced with a single colour light head. I suspect that one of three things could occur -
1. They didn't get replaced but stayed semaphore.
2. For equal speed routes the colour light would clear for either route when set and cleared through - and remain On for a slower diverging route.
3. Where the junction Stop Signals were installed with double heads (rather than with lunar lights (feathers) the Distant could remain a Splitting Distant - being provided with two heads.
I would be very interested to know of any examples - especially of the last option.

One thing to note is that where there had previously been worked Splitting Distants it sometimes occurred that the through/dominant route remained a worked Distant while the diverging route, rather than completely losing its Distant gained a Fixed Distant. I assume that this was done to assist train crews in identifying exactly where they were on the line.

Essentially the bulk of the above applies to Absolute Block areas.

TC Block, with its ability to run on automatic and for route setting (NX panels and similar) changed things a bit.
For the most part the principle that a slow diverging route would be protected by a single yellow worked the same as a Fixed Distant or the Distant always On for the diverging route.
As/when train speeds increased with better braking (rather than with loco power) the use of Flashing Distants was introduced. This was still not "digital" - it was just a step toward it.

----

One slightly obscure thing to point out...

In early (semaphore/AB) signalling days it seems that there was some use of not just Splitting Distants but Splitting Outer Homes in addition to Splitting Inner Homes. I have seen this documented but never seen a picture of it applied on the ground. It would, admittedly, be quite difficult to identify it in most photographs (and there are relatively few anyway). So far I have no information on where or when this arrangement may have been applied - and no information about when the practice ceased.

----

I think that I have covered the main issues...









* Does anyone else recall the days when we thought that computers were fast - while we waited for them to squeak, groan and chunter as they loaded up??? Compared to the instant frustration today if the screen doesn't change instantly those sounds were quite relaxing...
--- old post above --- --- new post below ---
Ah!!! Thought of another thing...

With an Absolute Block Box...

At the junction...

In standard Block Working, when a train is given as "Entering Section" by the Box In Rear the Junction Box will Bell it forward ("knock it on") to the next Box (Box In Advance) that it is expected that it will be going to as soon as the Block Section In Advance is "Normal" (on 3 position Block). Then, in normal working, as soon as a "Line Clear" is received the Junction Box will set the route and clear the signals right through.
If, subsequently, it proves that the wrong route has been set it will be necessary to restore the signals to Stop/Danger, cancel off the accepted train and offer it on to the correct Box In Advance. This should not take long - but, where "time-outs" or "wind-outs" are included in the interlocking a few minutes might be added.

 

[DerekC]

Which means it can be on a signal without a matching berth



On a signal



On a signal


Not sure if you were trying to prove my point or not.

We have the GSMR plate which basically gives the area code (blue with white lettering)

There is also a GSMR plate instructing the use of a 99X code

And I believe there is one that is similar to the standard alias plate and it instructs the use of a setup code (basically the same as an alias plate) Its white with black lettering. Some also have a telephone number. I've not seen one in use yet but could they be what your after ?

Thanks for the info. Not trying to prove anybody's point - just trying to work out how the system is used in practice.

 

[edwin_m]

I am realising that I have not previously considered what happened with splitting semaphore Distants when they were replaced with a single colour light head. I suspect that one of three things could occur -
1. They didn't get replaced but stayed semaphore.
2. For equal speed routes the colour light would clear for either route when set and cleared through - and remain On for a slower diverging route.
3. Where the junction Stop Signals were installed with double heads (rather than with lunar lights (feathers) the Distant could remain a Splitting Distant - being provided with two heads.
I would be very interested to know of any examples - especially of the last option.

1. Unlikely. When an area was re-signalled all the semaphores would be replaced by colour-lights. It's possible there would be a "spot" replacement of a stop signal by a colour light, leaving the distant as a semaphore, but the other way round would be much more likely. The LMS for example replaced many of its main line distants with colour lights which made them more visible to drivers and also allowed them to be moved out to get more braking distance without having to worry about the length of the wire pull.

2. Yes. These are the situations where the driver probably doesn't have enough warning of which route is set to stop short of the junction if it is the wrong one.

3. Yes, occasionally with older colour light schemes including replacement of semaphore distants. Probably the most famous was the three-way at Ely North Junction, now preserved in someone's garden, for which Google will no doubt find pictures. These have also been included in a few more recent schemes - I think Heathrow Junction was the first of these - but they aren't exactly common. For a three-aspect version all the heads show a yellow except the one applying to the route set (if any) which shows green. There are also four-aspect versions including "outer splitting distants" displaying multiple double yellows.

Also:

4. Approach control (sometimes known as approach release). The more recent equivalent of only clearing the distant for the primary route. For other routes the junction signal would remain at red until released by track circuit occupation and a timer to show a route indicator and proceed aspect only when the train must be approaching slowly enough to take the junction. Unpopular because it often slows trains unnecessarily early and because there is a risk of drivers anticipating the signal clearing when it doesn't, leading to a dangerous SPAD on the approach to a junction. There is also the possibility of approach control from single yellow but I think it was largely superseded by flashing yellows.

5. Flashing yellow at the signal preceding the junction signal, and in four-aspect areas flashing double yellow at the one before that. These aspects are displayed for the second most important route from a junction, and to reduce confusion no signal can be capable of displaying more than one flashing aspect. The junction signal is held at single yellow with feather and clears to the appropriate aspect as the train approaches.

6. Preliminary routeing indicators as above.

7. One I forgot. In the early days (particularly with the LMS distant replacements in the 1930s) the double yellow aspect could be used to mean "diverging route clear ahead". For obvious reasons this wasn't used for very long.

 

[najaB]

Probably the most famous was the three-way at Ely North Junction, now preserved in someone's garden, for which Google will no doubt find pictures.

I presume you're talking about the signal shown at the bottom of this page.

 

[Railsigns]

In early (semaphore/AB) signalling days it seems that there was some use of not just Splitting Distants but Splitting Outer Homes in addition to Splitting Inner Homes. I have seen this documented but never seen a picture of it applied on the ground. It would, admittedly, be quite difficult to identify it in most photographs (and there are relatively few anyway). So far I have no information on where or when this arrangement may have been applied - and no information about when the practice ceased.

That is actually current practice, mandated by section 5.3.1.4 of Group Standard GK/RT0045.

Also illustrated by a diagram on page 83 of the relevant Guidance Note, GK/GN0645.

 

[edwin_m]

I presume you're talking about the signal shown at the bottom of this page.

That's the one. I hadn't remembered it was also the starter for Ely Station North.
--- old post above --- --- new post below ---

That is actually current practice, mandated by section 5.3.1.4 of Group Standard GK/RT0045.

Also illustrated by a diagram on page 83 of the relevant Guidance Note, GK/GN0645.

I very much doubt any semaphore splitting distants still exist, so I suspect this clause is no longer relevant. Does anyone know for sure?

 

[Railsigns]

I very much doubt any semaphore splitting distants still exist, so I suspect this clause is no longer relevant. Does anyone know for sure?

No semaphore splitting distant signal has existed since the last one was removed in 2007 and they're not allowed in new works; however, section 5.3.1.4 would still apply in a situation where the splitting distant is a colour light and the junction signal is a semaphore.

 

[John Webb]

........
7. One I forgot. In the early days (particularly with the LMS distant replacements in the 1930s) the double yellow aspect could be used to mean "diverging route clear ahead". For obvious reasons this wasn't used for very long.

We have the original LMS document at St Albans South regarding the replacement in late 1938 of the down semaphore distant signals on the approach to St Albans City station. At St Albans South there was a cross-over from Down Slow to Down Fast, so the down slow distant was capable of showing two yellows, whereas the second aspect on the down fast distant was merely the auxiliary aspect for use if the main aspect failed. There is a brief (undated) note in an entirely different hand deleting the double yellow display; we think this may be after the Bourne End accident in September 1945, following which this indication was generally discontinued.

 

[D Foster]

That is actually current practice, mandated by section 5.3.1.4 of Group Standard GK/RT0045.

Also illustrated by a diagram on page 83 of the relevant Guidance Note, GK/GN0645.

Hmmm... That's interesting...

I have seen a hard copy of the Group Standards (probably a fairly ancient one by now) and not taken this in.

The thing is - that I note that the title is "Guidance on Lineside Signals, Indicators and Layout of Signals".

There's more than plenty of locations that I haven't seen around the country - but I have no recall of ever seeing signals arranged in this way. Please does anyone know of (preferably know of a picture or two) of this arrangement... Any date will be helpful. I can't even think of a Box Diagram that I have seen that had this arrangement.
I'm not "arguing" - I am very intrigued.

Thanks for enlightening me on this.

 

[Railsigns]

The thing is - that I note that the title is "Guidance on Lineside Signals, Indicators and Layout of Signals".

Yes, but the associated group standard is mandatory. I nearly fell off my seat when I saw this long-discontinued practice appear in the re-issued standard some years ago. I doubt there will ever be an occasion when it's put into practice on the modern railway.

Here is an example of an actual layout from the distant past:

http://www.signalbox.org/diagrams.php?id=93

 

[D Foster]

Yes, but the associated group standard is mandatory. I nearly fell off my seat when I saw this long-discontinued practice appear in the re-issued standard some years ago. I doubt there will ever be an occasion when it's put into practice on the modern railway.

Here is an example of an actual layout from the distant past:

http://www.signalbox.org/diagrams.php?id=93

I'm so glad that the example is dated 1930! I am not that old! (Just feel it sometimes).

The next question that arises is whether a "mandatory" standard has been ignored for years? An alternative would seem to be that it was, perhaps, dropped at some point but then crept back in - to cause people to nearly fall off their chairs?

The really impressive/scarey thing for me is that you can locate examples so fast! hock:

Thanks

Are there any more examples please?

 

[Railsigns]

I'm so glad that the example is dated 1930! I am not that old! (Just feel it sometimes).

I have just read that one of the last examples, at Whitland West, was removed in 1966.

The next question that arises is whether a "mandatory" standard has been ignored for years? An alternative would seem to be that it was, perhaps, dropped at some point but then crept back in - to cause people to nearly fall off their chairs?

The practice was most certainly dropped then crept back into modern standards.

 

[D Foster]

How very weird!!!

It's yet another example of the need for route knowledge among train crews.

I wonder if it's possible to determine the places at which it remained... or should I say "didn't get removed"?

Then again, if it's come back into prescribed practice... Is there anywhere that we can now see it to have been applied after its return?

One issue is - that providing double colour light heads rather than a single head with lunar lights stopped happening... Sometime... I have no idea when... Although there were still twin heads at Earlswood (TCB/multiple aspect from Three Bridges and round The Quarry Diversion - AB to Redhill A). The point being that, if twin heads had gone out of use - it would seem that an advance indication of the junction would have meant a signal with a lunar light display. This would appear to still be the case - according to the standard...
Am I getting something wrong in this interpretation?

Those signals at Earlswood got altered/replaced when the Three Bridges scheme was commissioned about 1980/1/2(ish) (I really should know - 'cos I was there...)

--- old post above --- --- new post below ---
Hmmmm...

I'm thinking that maybe the effectively additional signal arm didn't get removed because that could have meant that a lever in the frame would have become redundant - and that could have meant an alteration of the interlocking would be necessary... Although I could see several possible ways to simplify that - mainly by using some form of electrical locking arrangement - or perhaps a white/brown lever???

So - another question would be whether the places the arrangement remained in use would have had a particular kind of interlocking that didn't lend itself to alteration?

I'm just "musing"...



I'm also recalling that up to that time the other end of the Quarry - Coulsdon North (aka "Stoatsnest") had the combination of semaphore Stop arms with colour light aspects required for the changeover from AB/semaphore to TCB/colour light. This was the only place I ever saw this. Annoyingly I failed to take pictures of the signals at both ends of the Quarry