Another Signal Poser!

[Chrius56000]

. . .What's the reason why old semaphore installations never had signal number–plates on brackets, gantries, signal–posts, etc?

. . .I have noticed where Semaphores remain and are still in use, N.R. is gradually adding identification plates to them, but look at any railway signalling book or photo album of traction, regions or a particular line or area, and you almost never see a semaphore with an identification plate!

. . .Contrast this with colour–light signals which have always had an identification plate since they were first used on the Marylebone/Amersham/Neasden main–line route in 1923! (The L.O.R. first used automatic colour–light signalling as early as 1921 but I don't think their signals had number plates!)

. . . Incidentally in otherwise semaphore AB areas I believe colour–light distants never originally had a number plate either, am I correct?

. . .I have noticed modernised AB lines such as Leicester–Manton–Peterborough where much original signalling has been modernised with LED single–lens aspect units, these do have number–plates but the fairly high speeds at which the Class 170 dmus pass them on this line means I can't read them!

Chris Williams

 

[edwin_m]

At a guess, they never had number plates because the thought never occurred to anybody to display them. When a driver or fireman reported to the signal box under Rule 55 he would simply rely on route knowledge to say he was at the inner home or the advance starter. And yes I think you're right colour light distants in otherwise semaphore areas didn't carry numbers either.

When colour lights came along there was no obvious way of telling one from another so they had to be given number plates, which also identified to the signalman where a driver was when using a signal post telephone. Then somebody probably decided it was inconsistent that semaphore signals didn't have plated numbers (they always had lever numbers) so plates were added...

Is there ever an operational need to read a signal number plate when passing at high speed? It would be easier for a driver to do so than a passenger though.

 

[30907]

The change would have been needed as soon as boxes started to control more than one AB section - did semaphore Intermediate Block signals have them from the start?

 

[Rescars]

Presumably the first plates fitted to semaphore signal were the track circuit, telephone and call plunger symbols which showed that a Rule 55 walk to the signal box was not necessary.

 

[Railsigns]

I recall that it was a SPAD at Prudhoe that led to the widespread fitment of ID plates to semaphore signals. That was back in Railtrack days.

 

[thesignalman]

Number plates were never necessary in Absolute Block areas because all signals (semaphore or colour-light) could be identified identified by name - e.g. "Up Home". Intermediate Block Signals were not numbered, either.

They only carry them today in the interests of standardisation and consistency. And perhaps for the benefit of drivers with no memory retention. Distant signals should never be numbered, even today, because trains are not detained at them - although many (perhaps most?) now are. Its a different world now, no longer based on need or practicality but on pages of "standards" created by desk boys.

John

 

[Ken H]

Number plates were never necessary in Absolute Block areas because all signals (semaphore or colour-light) could be identified identified by name - e.g. "Up Home". Intermediate Block Signals were not numbered, either.

They only carry them today in the interests of standardisation and consistency. And perhaps for the benefit of drivers with no memory retention. Distant signals should never be numbered, even today, because trains are not detained at them - although many (perhaps most?) now are. Its a different world now, no longer based on need or practicality but on pages of "standards" created by desk boys.

John

Signal numbers may be used in records. So you can record 'bulb changed in SJ7' and look back and see when the bulb was last changed. All sorts of stuff is numbered these days to assist in maintenance.

 

[Gloster]

You only need number-plates at signals that a train might be stopped at. Trains are not normally stopped at Distants, as they have no red aspect, so they don’t need a plate.

 

[edwin_m]

Signal numbers may be used in records. So you can record 'bulb changed in SJ7' and look back and see when the bulb was last changed. All sorts of stuff is numbered these days to assist in maintenance.

It's also useful for the technician sent out to change said bulb (which they would probably refer to as a lamp, signalling people being snooty that way) to make sure they've gone to the correct signal.

 

[Rescars]

It's also useful for the technician sent out to change said bulb (which they would probably refer to as a lamp, signalling people being snooty that way) to make sure they've gone to the correct signal.

And not necessary back in the day, when each signal lamp would need a weekly visit to refill the oil reservoir and trim the wick.

 

[flowcoach]

It's also useful for the technician sent out to change said bulb (which they would probably refer to as a lamp, signalling people being snooty that way) to make sure they've gone to the correct signal.

In order to safely get to the signal, the technician may need to have a blockage or a possession in place. The physical limits of that protection are often defined by the signals at either end of it. Clear and concise communication about which signals are in question is therefore essential.

 

[Chrius56000]

. . .Another thought I had is that on modernised AB lines like Leicester – Manton – Peterborough where signals have been replaced with single–unit LEDs over a fair length of line, it isn't readily distinguishable between 2–aspect and 3–aspect signalling, and as green in 2–aspect territory could easily be followed by a red (e.g., home and starter) so identifying distants in such areas (which I think is done with a vertical triangle and well as an "R/RR" suffix to the signal number) would help a driver as seeing a green plated as a distant means all subsequent signals of that type will be "off" as far as the next distant at least!

Chris Williams

 

[midland1]

. . .Another thought I had is that on modernised AB lines like Leicester – Manton – Peterborough where signals have been replaced with single–unit LEDs over a fair length of line, it isn't readily distinguishable between 2–aspect and 3–aspect signalling, and as green in 2–aspect territory could easily be followed by a red (e.g., home and starter) so identifying distants in such areas (which I think is done with a vertical triangle and well as an "R/RR" suffix to the signal number) would help a driver as seeing a green plated as a distant means all subsequent signals of that type will be "off" as far as the next distant at least!

Chris Williams

With colour light you never get a green followed by a red, the green (the home) would be a yellow leading to a red (the starter).

 

[Chrius56000]

With colour light you never get a green followed by a red, the green (the home) would be a yellow leading to a red (the starter).

. . . Theoretically not, but before Blackrod to Manchester came under control of Manchester Piccadilly S C.C. in 1988 this sometimes did happen – the Blackrod Station Starter was a two–aspect R/G colour–light and it wasn't unknown to get green at this and then red on the "Home" with the route indicator for Bolton's platforms – I had to commute from Lancaster to Manchester in those days to attend a Training Course at Trafford Park Skill centre!

 

[Gloster]

If the colour light is effectively replacing a semaphore stop signal, then it will display the same aspects: red and green. You can have colour light signals in Absolute Block areas and they will function in the same way as semaphores. The driver should know what aspects the signal will show: if colour light AB is effectively a Home Signal and, if he has been checked at a Distant, he will know that a Green at AB does not mean that the semaphore Starter is at Clear, although he should be checked down by the box. (I think that this arrangement was never very common and is becoming increasingly rare, if it hasn’t already been eliminated.)

 

[thesignalman]

If the colour light is effectively replacing a semaphore stop signal, then it will display the same aspects: red and green. You can have colour light signals in Absolute Block areas and they will function in the same way as semaphores. The driver should know what aspects the signal will show: if colour light AB is effectively a Home Signal and, if he has been checked at a Distant, he will know that a Green at AB does not mean that the semaphore Starter is at Clear, although he should be checked down by the box. (I think that this arrangement was never very common and is becoming increasingly rare, if it hasn’t already been eliminated.)

That's just not true. A colour-light home signal in an AB area would show R/Y/G. Yellow when the starter (or other stop signal ahead) is on, and green when all signals controlled by the one box are off. Excepting Intermediate Block signals, if they exist, of course.

John

 

[Lucy1501]

A colour-light home signal in an AB area would show R/Y/G.

Not neccessarily. There's even still rulebook provisions for not clearing a colour light signal that can't show a yellow until the train is checked at it, much like ordinary semaphore stop signals. Although I do admit, R/Y/G is the standard nowadays and new R/G installs leading up to another stop signal aren't permitted.

The Liverpool Loop Line, though TCB, has many places where you can go from red to green with no yellow as well.

 

[thesignalman]

Not neccessarily. There's even still rulebook provisions for not clearing a colour light signal that can't show a yellow until the train is checked at it, much like ordinary semaphore stop signals. Although I do admit, R/Y/G is the standard nowadays and new R/G installs leading up to another stop signal aren't permitted.

The Liverpool Loop Line, though TCB, has many places where you can go from red to green with no yellow as well.

I'm not sure where you get that from and would be very interested to see the Rule you are quoting. What you say is completely against the Principles of Signalling and I cannot visualise any such circumstance past or present.

Two-aspect TCB operation is not relevant to the question.

John

 

[Lucy1501]

very interested to see the Rule you are quoting.

Here’s two extracts from the current Rulebooks:

 

[thesignalman]

Thank you. Well, that is fascinating indeed. I cannot think of a single circumstance where the first bullet point of 1.6 could possibly apply, and wonder how that crept into the current rules. Quite bizarre.

John

Update . . .

Retracting what I said earlier, the Liverpool Loop is not two-aspect TCB as such, it seems to be special signalling for that line alone. I found a description of it at https://www.simsig.co.uk/Wiki/Show?page=simulations:sandhills which describes operation as:

Loop Line Signalling​

All Stop signals between Green Lane / Birkenhead Part and around the Liverpool Loop Line are two aspect (Red/Green). As repeaters are not provided for all signals, it is possible for a Green-> Red aspect sequence to be displayed to drivers. Unusually, however, there are no restrictions on operating these signals- they may be cleared at any time, and drivers will accept a Green-> Red aspect sequence without a Yellow aspect, or delayed clearance of the preceding signal.

That kind of line (it may be the only one) would seem to be the sole reason for that clause in the rules. I guess it is very similar to London Transport signalling.

John