Semaphore distants - speed signals?

[eldomtom2]

I have heard it claimed (by someone who claims to know what they're talking about) that UK semaphore distants are speed signals, because 1) they cover multiple stop signals, any one of which being at stop places the distant at caution, and 2) a distant may be at caution even if no stop signals are at stop, e.g. when a train is being routed to a slower diverging route. Thus the argument is that a UK distant is not a block signal and conveys no information to the driver besides "slow down". Is there any truth to this argument?

 

[Trothy]

A distant signal is just that, a distant signal.

It's not a speed signal as there isn't such a thing.

I'm not really sure what you are asking?

 

[MarkyT]

I have heard it claimed (by someone who claims to know what they're talking about) that UK semaphore distants are speed signals, because 1) they cover multiple stop signals, any one of which being at stop places the distant at caution, and 2) a distant may be at caution even if no stop signals are at stop, e.g. when a train is being routed to a slower diverging route. Thus the argument is that a UK distant is not a block signal and conveys no information to the driver besides "slow down". Is there any truth to this argument?

A distant at caution always means be prepared to stop at the first stop signal encountered, which must be at least braking distance from the distant. For a simple slow diverging route scenario at the home, the distant remains at caution while the junction signal is also held at danger. Only as the train approaches the junction 'under control' does the signaller then finally pull off for the divergence. If a higher speed was desired, then a 'splitting distant' arrangement might be used, giving the driver advance notice of which route is set.

 

[zwk500]

I have heard it claimed (by someone who claims to know what they're talking about) that UK semaphore distants are speed signals, because 1) they cover multiple stop signals, any one of which being at stop places the distant at caution, and 2) a distant may be at caution even if no stop signals are at stop, e.g. when a train is being routed to a slower diverging route. Thus the argument is that a UK distant is not a block signal and conveys no information to the driver besides "slow down". Is there any truth to this argument?

No, a distant signal is an indication of the condition of the aspect ahead - it means 'Expect stop'. It conveys no information of a specific speed being required.

It's not a speed signal as there isn't such a thing.

There is in other countries.

 

[Ashley Hill]

It's not a speed signal as there isn't such a thing

The LMS tried it in the 1930s. Here’s a link to the Signal Box site where it’s explained.

LMS Speed Signalling – The Signal Box

signalbox.org

 

[Rescars]

Presumably a fixed distant has the effect of acting as a speed signal, as the driver must always proceed with sufficient caution to stop at the next signal.

 

[Irascible]

I think a distant only covers multiple stop signals in absolute block ( but you'd still be expected to be able to stop at the first one anyway ). Are there non-AB semaphores around?

I guess approach release might be thought of as speed signalling, but ...semaphore?

 

[zwk500]

Presumably a fixed distant has the effect of acting as a speed signal, as the driver must always proceed with sufficient caution to stop at the next signal.

But it doesn't though. It just means 'expect Stop at any of the next Stop signals'. A Fixed distant conveys no speed authority either way to the driver. They rely on their route and traction knowledge to ensure they drive at an appropriate signal.

I think a distant only covers multiple stop signals in absolute block ( but you'd still be expected to be able to stop at the first one anyway ). Are there non-AB semaphores around?

There are a couple of fixed distant boards in 2- (or possibly 3-) Aspect areas I think which are pictures of a Semaphore distant, but whether they are truly 'semaphores' is debatable.

I guess approach release might be thought of as speed signalling, but ...semaphore?

Approach release isn't speed signalling though, because it could just as easily be a signal check for a train in front as it is the diverging route. Flashing Aspects isn't even speed signalling (although it's the closest standard UK practice comes to it) as it doesn't tell you what the authorised speed actually is, just that you're turning out. At all times it is still drivers' route knowledge and lineside signage that informs them what the actual authorised speed is.

 

[matchmaker]

But it doesn't though. It just means 'expect Stop at any of the next Stop signals'. A Fixed distant conveys no speed authority either way to the driver. They rely on their route and traction knowledge to ensure they drive at an appropriate signal.

There are a couple of fixed distant boards in 2- (or possibly 3-) Aspect areas I think which are pictures of a Semaphore distant, but whether they are truly 'semaphores' is debatable.

Approach release isn't speed signalling though, because it could just as easily be a signal check for a train in front as it is the diverging route. Flashing Aspects isn't even speed signalling (although it's the closest standard UK practice comes to it) as it doesn't tell you what the authorised speed actually is, just that you're turning out. At all times it is still drivers' route knowledge and lineside signage that informs them what the actual authorised speed is.

Before Stirling Middle was resignalled with colour lights, there was a motor operated semaphore distant leading on to the entirely colour light and track circuit block Alloa/Kincardine line. It had as far as I can remember a SK number rather than its original SN number, which suggests that it would have been operated from the Alloa line NX panel rather than the lever frame.

 

[zwk500]

Before Stirling Middle was resignalled with colour lights, there was a motor operated semaphore distant leading on to the entirely colour light and track circuit block Alloa/Kincardine line. It had as far as I can remember a SK number rather than its original SN number, which suggests that it would have been operated from the Alloa line NX panel rather than the lever frame.

Interesting, I imagine there were a few more exceptions like that around fringe areas during the 70s/80s.

 

[Wilts Wanderer]

Definitely not a speed signal. A speed signal is an aspect that is literally an instruction to “proceed at X speed” which we do not have in this country, except on HS1 and, in theory, the Cambrian and Heathrow lines (although it’s slightly more complicated with ETCS.)

European signalling is generally speed-based, different coloured aspects instructing to proceed at a particular speed but providing little or no routing information. UK signalling is route-based, so the signal aspect provides full routing info but the driver is expected to know their maximum speed from route knowledge, supported by lineside signage in most places.

 

[Annetts key]

I have heard it claimed (by someone who claims to know what they're talking about) that UK semaphore distants are speed signals, because 1) they cover multiple stop signals, any one of which being at stop places the distant at caution, and 2) a distant may be at caution even if no stop signals are at stop, e.g. when a train is being routed to a slower diverging route. Thus the argument is that a UK distant is not a block signal and conveys no information to the driver besides "slow down". Is there any truth to this argument?

So, first, be careful of people who claim they know what they're talking about.

As others have said, the purpose of semaphore distant signal is to provide drivers of sufficient warning that there is a stop signal at danger ahead, and that the driver should use their knowledge of the traction/train and the route to control the speed such that the train can stop short of the signal at danger ahead. Or to put it another way, the semaphore distant signal is spaced at service braking distance from the stop signal.

Secondly, if a semaphore distant signal is being counted as a speed signal, then a stop signal or a signal displaying a red aspect (with no other proceed aspect) can be listed as a speed signal, as it instructing a driver that the speed is zero beyond it!

 

[172007]

I think a distant only covers multiple stop signals in absolute block ( but you'd still be expected to be able to stop at the first one anyway ). Are there non-AB semaphores around?

I guess approach release might be thought of as speed signalling, but ...semaphore?

Yes there are some non-ab semaphore signals. The Through Siding at Tyseley behind the carriage sidings and fueling Rd are "No Block and entry exit are by Semaphore one end and Colour light the other.

 

[12LDA28C]

It's also entirely possible of course to have a colour light distant signal for a semaphore stop signal.

And to those people talking of 'approach release' signals - I'd get my arse kicked in a Rules exam for saying that. The correct terminology would be 'approach controlled'. You should never expect the signal to come off and instead, be prepared to stop.

 

[hexagon789]

It's also entirely possible of course to have a colour light distant signal for a semaphore stop signal.

In Scotland, all but one distant for a semaphore home signal is a colour light now.

The only surviving semaphore distant in Scotland is on the Stranraer line on the down approaching Glenwhilly.

 

[Uranquinty]

It may be worth addiing this into the discussion: a transcript of LMS document ERO 50239: “Instructions as to the Sighting of Signals”. This was printed in 1936; but containing the Ministry of Transport guidance from 1928 and of itself an amplification of the 1925 notice that mandated the use of yellow glass in addition to red and green.

These are the relevant sections for Distant signals:

• Up and Down Distant Signals for each block post, to be provided on all running lines which have two position stop signals. One Distant Signal in each direction, with the necessary control from each Signal Box, is sufficient for a number of block posts closely grouped together, unless there are good reasons to the contrary.
• At diverging junctions only one Distant Signal should be provided, worked for the junction line over which the highest speed is permissible, unless in exceptional circumstances more are essential. Where special circumstances, e.g. permanent speed restrictions, justify the adoption of an un-worked signal, it should be secured in the warning position and not coupled up or duplicated for directing purposes.
• The interval between a Distant Signal and the first Stop Signal to which it applies must be such that a train in proximity to the former, and moving at the highest speed can be stopped before passing the latter.
• All signals, as a rule to be immediately on the left of, or vertically over, the line to which they apply.
• Semaphore Distant Signals to be distinguished from Stop Signals during daylight hours by yellow coloured arms, with notches cut out of the ends. They must be placed below, and be controlled by Stop Signals, if they are carried on the same post and applicable to the same direction. A Distant Signal placed under a Stop Signal of a box in the rear must, unless the circumstances are exceptional, be repeated under all Stop Signals in advance of that signal which are worked from that box, with the necessary additional control by such signals.
• Front lights of all running signals to be red for Danger, yellow for Caution (including the warning position of Distant Signals), and green for clear, with white used for backlights to be only visible when the signal is at Danger.

 

[The Puddock]

Before Stirling Middle was resignalled with colour lights, there was a motor operated semaphore distant leading on to the entirely colour light and track circuit block Alloa/Kincardine line. It had as far as I can remember a SK number rather than its original SN number, which suggests that it would have been operated from the Alloa line NX panel rather than the lever frame.

SK6503 - it came off by itself when the signal ahead (SK6515) was showing a proceed aspect but had a replacement switch on the panel if it needed to be held at caution for some reason.

 

[Llanigraham]

In Scotland, all but one distant for a semaphore home signal is a colour light now.

The only surviving semaphore distant in Scotland is on the Stranraer line on the down approaching Glenwhilly.

Dorrington, Marshbrook, Craven Arms, Bromfield and Woofferton are all semaphore home with colour light distant.
I think the rest of the Boxes down the Marches are the same.
Onibury, in the middle, is all colour light.

 

[hexagon789]

Dorrington, Marshbrook, Craven Arms, Bromfield and Woofferton are all semaphore home with colour light distant.
I think the rest of the Boxes down the Marches are the same.
Onibury, in the middle, is all colour light.

Was Onibury resignalled or rationalised at some point?

BR seemed to have a knack of replacing a lot of distant semaphores with colour lights but leaving the home and starters alone.

I always assumed it was to improve sighting for the distant? Particularly in fog or poor visibility.

 

[30907]

Was Onibury resignalled or rationalised at some point?

BR seemed to have a knack of replacing a lot of distant semaphores with colour lights but leaving the home and starters alone.

I always assumed it was to improve sighting for the distant? Particularly in fog or poor visibility.

Very often increased braking distance for higher speeds - I know the LMR did, and the SR (SW at least). Thus avoiding a very long wire run AND dispensing with the fogman as a bonus!

 

[Llanigraham]

Was Onibury resignalled or rationalised at some point?

BR seemed to have a knack of replacing a lot of distant semaphores with colour lights but leaving the home and starters alone.

I always assumed it was to improve sighting for the distant? Particularly in fog or poor visibility.

If I remember correctly Onibury was resignalled when the moved the Box across the road and built the "shed".

We were told that the reason the Distants were colour lighted was the length of the wire runs and the problems in maintaining them, and it was cheaper to change them to lights than motorise the semaphores. Now all those I have listed have been changed from filament units to LEDs. I don't think sighting or visibilty came into it.

 

[hexagon789]

Very often increased braking distance for higher speeds - I know the LMR did, and the SR (SW at least). Thus avoiding a very long wire run AND dispensing with the fogman as a bonus!

I was going to suggest that, but then I considered my own region - the Scottish.

Here I understand many distants were replaced with colour lights back when maximum linespeed was still 75mph throughout the region.

== Doublepost prevention - post automatically merged: 31 May 2023 ==

We were told that the reason the Distants were colour lighted was the length of the wire runs and the problems in maintaining them, and it was cheaper to change them to lights than motorise the semaphores. Now all those I have listed have been changed from filament units to LEDs.

I can understand that - easier to maintain.

 

[Railsigns]

Here I understand many distants were replaced with colour lights back when maximum linespeed was still 75mph throughout the region.

Another factor was the provision of AWS, which was fitted at distant signals but not at semaphore stop signals (unless co-located with a distant).

It used to be accepted practice to take sighting distance into account when siting distant signals; i.e., it was presumed that a driver would commence braking on sighting a distant signal at 'caution' and not leave it until the train reached the signal. Under these conditions, an AWS intervention at the distant signal couldn't be relied on to stop the train before it reached the home signal. There has to be full braking distance between the distant and home signals, so a lot of distant signals were moved further out when AWS was fitted.

Aside from that, replacing a semaphore distant signal with a colour light equivalent is relatively straightforward, whereas doing the same with semaphore stop signals can throw up all sorts of issues.

 

[eldomtom2]

It may be worth addiing this into the discussion: a transcript of LMS document ERO 50239: “Instructions as to the Sighting of Signals”. This was printed in 1936; but containing the Ministry of Transport guidance from 1928 and of itself an amplification of the 1925 notice that mandated the use of yellow glass in addition to red and green.

These are the relevant sections for Distant signals:

• Up and Down Distant Signals for each block post, to be provided on all running lines which have two position stop signals. One Distant Signal in each direction, with the necessary control from each Signal Box, is sufficient for a number of block posts closely grouped together, unless there are good reasons to the contrary.
• At diverging junctions only one Distant Signal should be provided, worked for the junction line over which the highest speed is permissible, unless in exceptional circumstances more are essential. Where special circumstances, e.g. permanent speed restrictions, justify the adoption of an un-worked signal, it should be secured in the warning position and not coupled up or duplicated for directing purposes.
• The interval between a Distant Signal and the first Stop Signal to which it applies must be such that a train in proximity to the former, and moving at the highest speed can be stopped before passing the latter.
• All signals, as a rule to be immediately on the left of, or vertically over, the line to which they apply.
• Semaphore Distant Signals to be distinguished from Stop Signals during daylight hours by yellow coloured arms, with notches cut out of the ends. They must be placed below, and be controlled by Stop Signals, if they are carried on the same post and applicable to the same direction. A Distant Signal placed under a Stop Signal of a box in the rear must, unless the circumstances are exceptional, be repeated under all Stop Signals in advance of that signal which are worked from that box, with the necessary additional control by such signals.
• Front lights of all running signals to be red for Danger, yellow for Caution (including the warning position of Distant Signals), and green for clear, with white used for backlights to be only visible when the signal is at Danger.

I can't help but notice that you've appeared to have copied this from the thread on another forum that led me to make this thread in the first place...

 

[Uranquinty]

I can't help but notice that you've appeared to have copied this from the thread on another forum that led me to make this thread in the first place...

Oh, indeed.

The wording from the Ministry of Transport illustrates that when you drill down into it conceptually a semaphore distant is a speed signal - the need to control the speed of the approaching train and the need to inform the driver of a speed restriction - yes, it is not a specified speed, save being less than that allowed in the Appendix.

 

[Llanigraham]

Oh, indeed.

The wording from the Ministry of Transport illustrates that when you drill down into it conceptually a semaphore distant is a speed signal - the speed of the approaching train and the need to inform the driver of a speed restriction - yes, it is not a specified speed, save being less than that allowed in the Appendix.

A Distant signal does NOT inform the driver of a speed restriction! It warns him of the aspect of the following Home signal.
As has been said several times.

 

[zwk500]

The wording from the Ministry of Transport illustrates that when you drill down into it conceptually a semaphore distant is a speed signal

No it doesn't. Not at all. A Speed signal conveys authority to move at a specified speed. The Distant gives no such restriction or authorisation. Conceptually, the Distant signal is a warning to the driver if he/she can expect to stop at the station or junction ahead. It does not inform the driver of a speed restriction in any way.

• At diverging junctions only one Distant Signal should be provided, worked for the junction line over which the highest speed is permissible, unless in exceptional circumstances more are essential. Where special circumstances, e.g. permanent speed restrictions, justify the adoption of an un-worked signal, it should be secured in the warning position and not coupled up or duplicated for directing purposes.

This rule specifies that the Distant signal should be able to be pulled off clear when the train is routed to the highest speed line at the layout. The literature says nothing about drivers interpreting the Distant signal as meaning a certain speed. It merely discourages the use of fixed distants for the highest speed line.

• The interval between a Distant Signal and the first Stop Signal to which it applies must be such that a train in proximity to the former, and moving at the highest speed can be stopped before passing the latter

This rule simply says that the Distant signal must be located a full braking distance prior to the first stop signal to which it applies for the line concerned.

 

[Annetts key]

The wording from the Ministry of Transport illustrates that when you drill down into it conceptually a semaphore distant is a speed signal - the need to control the speed of the approaching train and the need to inform the driver of a speed restriction - yes, it is not a specified speed, save being less than that allowed in the Appendix.

Maybe you can highlight which part of the quote says that a distant is a speed signal? Only my reading of the text you quoted clearly indicates that the purpose is as stated in my earlier post (#12). This part

The interval between a Distant Signal and the first Stop Signal to which it applies must be such that a train in proximity to the former, and moving at the highest speed can be stopped before passing the latter.

is clearly referring to what we now call service braking distance. That is, at the fastest permissible line speed, a train with a braking system that meets the minimum requirements, can stop before reaching the stop signal if the driver applies the brakes at time the train is at, or approaching the distant signal. That is not speed signalling.

 

[Uranquinty]

So if a distant is not a speed signal, it does not tell the driver to control their speed? <wink> A distant is unrelated to line speed <further wink>

Yes, yes - you can say it means "expect stop", but how else can you stop if not by controlling your speed?

 

[zwk500]

A distant is unrelated to line speed

Yes. 100%. No if's, buts, or winks about it.

Yes, yes - you can say it means "expect stop", but how else can you stop if not by controlling your speed?

The Distant does not change the authorised speed - it is the driver's judgement at what speed they may safely approach the signal they are required to stop at. That is totally different from the concept of speed signal that explicitly changes the maximum authorised speed of the train.