Signalling Confusion

[sorry4thedelay]

Probably been asked before-

Need some guidance on Distant Signals within TCB please!
I understand Distant Signals are identified by a Triangle, an 'R' or an 'RR' for an outer, also having an ID plate identifying the Signal ahead that they are associated with....

What I don't understand is what happens when a Train passes the Distant Signal if it cannot display a 'Danger Aspect'?

If it turns to yellow does that mean the signal it is associated with is at Danger? Therefore the Stop Signal behind the Distant is now at Yellow, giving a sequence of Yellow, Yellow, Red?

Also where is the 'RR' used?

Thanks!

 

[4F89]

If the distant is "off", ie green, all associated stop signals are also "off". Route knowledge tells you how many stop signals this refers to.

Semaphore/semaphore replacement colour light signals are either yellow/green or red/green.

 

[_toommm_]

With a distant signal, it will show either yellow or green (or the equivalent for a semaphore signal). If the distant is showing green, the signal it is associated with will be green therefore creating a green - green sequence, but if it is showing yellow, the signal it is associated with is red therefore creating a yellow - red sequence.

 

[pompeyfan]

RR is used on 3 aspect distant signals that can show Green, double yellow, yellow. These signals are reasonably rare and relate to areas where there are several 3 aspect signals in close proximity, usually around a station.

 

[lammergeier]

RR is used on 3 aspect distant signals that can show Green, double yellow, yellow. These signals are reasonably rare and relate to areas where there are several 3 aspect signals in close proximity, usually around a station.

I believe these are becoming more common, AIUI they offen get installed when areas are resignalled in order to prevent the issues surrounding transitionary signals (3-4 aspect.) Certainly in a couple of areas I sign they've been installed recently.

 

[Tomnick]

Probably been asked before-

Need some guidance on Distant Signals within TCB please!
I understand Distant Signals are identified by a Triangle, an 'R' or an 'RR' for an outer, also having an ID plate identifying the Signal ahead that they are associated with....

What I don't understand is what happens when a Train passes the Distant Signal if it cannot display a 'Danger Aspect'?

If it turns to yellow does that mean the signal it is associated with is at Danger? Therefore the Stop Signal behind the Distant is now at Yellow, giving a sequence of Yellow, Yellow, Red?

Also where is the 'RR' used?

Thanks!

I reckon you’re overthinking it a bit. The distant signal “repeats” the associated stop signal in a very loose sense and only really from the driver’s point of view. Once the train’s passed it, it’s no longer of interest to the driver and it’ll almost always be replaced to its most restrictive aspect before the train reaches the associated stop signal (which obviously stays cleared - or should do! - until the train’s passed it).

RR signals are relatively rare still (those in a 3- to 4-aspect transition are usually not followed by another distant signal so wouldn’t be plated RR) but there’s a few about, e.g. approaching a four-aspect stop signal where the stop signal in rear is a long way away (SIMBIDS?).

 

[John Webb]

Probably been asked before-

Need some guidance on Distant Signals within TCB please!
I understand Distant Signals are identified by a Triangle, an 'R' or an 'RR' for an outer, also having an ID plate identifying the Signal ahead that they are associated with....

What I don't understand is what happens when a Train passes the Distant Signal if it cannot display a 'Danger Aspect'?

If it turns to yellow does that mean the signal it is associated with is at Danger? Therefore the Stop Signal behind the Distant is now at Yellow, giving a sequence of Yellow, Yellow, Red?

Also where is the 'RR' used?

Thanks!

In TCB areas it is usual to set the repeater to its caution aspect as, or after the train has passed it. This does not mean the signal it refers to is at caution. If you look down this page to an entry for July St Albans South box, News 2013 there is a set of three photos showing an LED banner signal adjacent to our box. The first photo shows the banner at the horizontal position while the signal it refers to ahead of the stopped train is showing green.

 

[sorry4thedelay]

But what happens if I have a sequence when driving of a Stop Signal displaying Yellow then the next signal is a Distant signal-, Could this be also Green or Yellow? Therefore having a possibility of two yellows? Is that possible?

 

[MarkyT]

The R and RR suffix system of numbering (sometimes using the letter 'P' instead) has not been used for some time on new schemes, and distant signals are preferably given unique 4 numeral identities preceded by the usual signalbox or route section code, just like any other signal. Signals that can't display a red aspect don't HAVE to be replaced automatically immediately after passage of a train, so a separate train detection section commencing just past the signal doesn't have to be provided especially to do this if it's not necessary for other reasons. The next train detection section boundary encountered beyond the signal (provided for other purposes) should be used to replace the distant to its most restrictive aspect if the stop signal it repeats is not passed before that.

 

[edwin_m]

But what happens if I have a sequence when driving of a Stop Signal displaying Yellow then the next signal is a Distant signal-, Could this be also Green or Yellow? Therefore having a possibility of two yellows? Is that possible?

If the next signal is a distant the stop signal will generally only be capable of showing red or green. That's a typical arrangement for low-density lines where the section between stops signals is very long and for several reasons it's undesirable to give a yellow to a driver when the red it relates to is so far away. Hence a separate distant is provided at only a bit more than braking distance from the stop signal. So the sequence would be R/G then Y/G then R/G or R/Y/G.

There may be an exception if the signal spacing requires a double yellow. The sequence R/YY/G then YY/Y/G then R/Y/YY/G may occur in four-aspect areas if the middle one of the three is in a tunnel where it's not considered appropriate to stop a train.

 

[PupCuff]

But what happens if I have a sequence when driving of a Stop Signal displaying Yellow then the next signal is a Distant signal-, Could this be also Green or Yellow? Therefore having a possibility of two yellows? Is that possible?

Assuming that the main signal was a 3 aspect signal, aside from any perhaps non-standard local arrangements, the only reason this would occur is if a fault (eg the green aspect was out) had occurred thus the most un-restrictive(?? sorry I haven't had enough coffee, there will be a word for it) aspect the signal could show would be a yellow. Of course, whether said main signal would even be fitted with a yellow aspect if in the normal circumstances it could only show Red or Green is a different matter entirely.

On an aside I've never quite 'got' the use of the term "distant" to describe signals on TCB which cannot show a red aspect. In my regional parlance it's always been a "repeater" which helps indicate the distinction between how these signals and an AB distant function.

 

[edwin_m]

On an aside I've never quite 'got' the use of the term "distant" to describe signals on TCB which cannot show a red aspect. In my regional parlance it's always been a "repeater" which helps indicate the distinction between how these signals and an AB distant function.

I think originally a repeater was assumed to follow the aspects of the signal it repeated, although displaying different aspects such as yellow instead of red. As mentioned above this changed as the repeater tended to be restored to its most restrictive aspect as the train passed. Somebody probably thought the term "repeater" was no longer accurate, and like a semaphore distant it had its own independent function.

 

[Eccles1983]

But what happens if I have a sequence when driving of a Stop Signal displaying Yellow then the next signal is a Distant signal-, Could this be also Green or Yellow? Therefore having a possibility of two yellows? Is that possible?

In the scenario you describe it's not possible and is a signalling irregularity.

I don't like the term repeater. A banner repeater is ok but repeater for signals just doesn't seem right.

 

[30907]

I think originally a repeater was assumed to follow the aspects of the signal it repeated, although displaying different aspects such as yellow instead of red. As mentioned above this changed as the repeater tended to be restored to its most restrictive aspect as the train passed. Somebody probably thought the term "repeater" was no longer accurate, and like a semaphore distant it had its own independent function.

Surely a repeater (banner or whatever) repeats exactly the aspect of the signal ahead, and is not a signal in its own right? It is there for sighting purposes, doesn't have to be at braking distance etc etc.
(I believe LT/LUL practice was different, and distants had an R suffix.)

 

[PupCuff]

Surely a repeater (banner or whatever) repeats exactly the aspect of the signal ahead, and is not a signal in its own right? It is there for sighting purposes, doesn't have to be at braking distance etc etc.
(I believe LT/LUL practice was different, and distants had an R suffix.)

What you describe, I would understand as a Co-acting signal.

A banner repeater doesn't always repeat exactly the aspect of a signal ahead. The closest would be, if there was a case where it is a three aspect banner repeater and a three aspect signal you could infer that if the BR is on then the signal will be at red, if the BR if off white then the signal will be yellow and if the BR is off green then the signal will be green; but even then once the train has passed the BR it will revert to on so it is still not always representing the aspect of the signal which it 'repeats'.

 

[edwin_m]

What you describe, I would understand as a Co-acting signal.

I agree, a co-actor shows exactly the same aspect as the main signal but may not show the route/junction indicator(s).

I believe by the strict definition a repeater should follow the behavior of the signal it repeats but won't show the same aspects (so a when acting as a distant for a three-aspect signal it would always show yellow for the main signal at red and green for it at yellow or green).

A distant has more functionality - in absolute block areas it has its own lever and if the box has more than one stop signal they must all be clear for the distant to be allowed to clear. In track circuit block areas it doesn't have its own control, but will generally revert to its most restrictive aspect once the train has passed it.

 

[PupCuff]

A distant has more functionality - in absolute block areas it has its own lever and if the box has more than one stop signal they must all be clear for the distant to be allowed to clear. In track circuit block areas it doesn't have its own control, but will generally revert to its most restrictive aspect once the train has passed it.

Indeed, hence why I feel there is a need to maintain the distinction between a "Distant" and a "Repeater"-or-whatever-else-you-might-want-to-call-it.

The only reason I can think of for when a repeater would not go back behind a train would be when the infrastructure does not allow it, eg due to the layout of the track circuit section, in other cases it would seem illogical for it not to go back if it could, despite the fact if a train's approaching it with the other train still in the section then something has gone quite wrong!

 

[Llanigraham]

A distant has more functionality - in absolute block areas it has its own lever and if the box has more than one stop signal they must all be clear for the distant to be allowed to clear.

To be pedantic, not necessarily; there are fixed distant signals.

 

[philthetube]

A co actor does not even have to be before the Signal, there are certainly a couple on the Underground which are beyond the signal they work with because of sighting issues.

Wembley park comes to mind where the stopping point on the north is approx 2' short of the signal, which is always red on arrival, Shock horror all main line drivers , and there is a co actor a couple of yards in advance of it.

 

[MarkyT]

The only reason I can think of for when a repeater would not go back behind a train would be when the infrastructure does not allow it, eg due to the layout of the track circuit section, in other cases it would seem illogical for it not to go back if it could, despite the fact if a train's approaching it with the other train still in the section then something has gone quite wrong!

Generally, designers don't HAVE to provide a special track circuit section purely to automatically replace a distant to most restrictive aspect, but a distant MUST be replaced at the NEXT train detection boundary encountered. There is usually a separate berth track circuit on final approach to a stop signal for example, used for approach release of certain routes or for temporary approach control, so occupation of that would replace the distant in rear.

 

[pompeyfan]

A co actor does not even have to be before the Signal, there are certainly a couple on the Underground which are beyond the signal they work with because of sighting issues.

Wembley park comes to mind where the stopping point on the north is approx 2' short of the signal, which is always red on arrival, Shock horror all main line drivers , and there is a co actor a couple of yards in advance of it.

waterloo platform 7 & 8 starters are 2 coach lengths behind the CA signal so it certainly happens on the mainline!

 

[Belperpete]

I agree, a co-actor shows exactly the same aspect as the main signal but may not show the route/junction indicator(s).

I believe by the strict definition a repeater should follow the behavior of the signal it repeats but won't show the same aspects (so a when acting as a distant for a three-aspect signal it would always show yellow for the main signal at red and green for it at yellow or green).

A distant has more functionality - in absolute block areas it has its own lever and if the box has more than one stop signal they must all be clear for the distant to be allowed to clear. In track circuit block areas it doesn't have its own control, but will generally revert to its most restrictive aspect once the train has passed it.

While I would generally agree, as noted by a previous poster, it has long been usual practice to replace both repeaters and banner repeaters if suitable train detection is available, but not to provide detection specifically just for this. This followed a number of accidents where a SPADing train encountered the repeater ahead at green, with a train just round the corner.

The terms distant, home, starter and section signals have specific meanings in absolute block areas. Unfortunately these terms have often been misapplied in TCB, causing confusion. As you say, in AB, the distant signal has to have its own control, as there are occasions when the signaller may have to maintain the distant on even though the stop signals are all off. Whereas with a repeater, the signaller generally does not have any control over the signal, other than by controlling the signal it is repeating.

 

[edwin_m]

Indeed. Even in a fairly well-controlled discipline such as signaling, railway jargon does tend to get mixed up and to mean different things to different people.

For what it's worth the signaling glossary states: https://catalogues.rssb.co.uk/rgs/standards/GKGN0802 Iss 1.pdf

Distant Signal: A Signal (not itself a Stop Signal) capable of displaying a Cautionary Aspect that informs the driver of the state of the Signals or Level Crossing ahead.

Repeater: an alternative term for an Indicator (Signal Box).

Indicator (Signal Box): A visual device which displays the position or condition of an item of signalling equipment.

Repeater Signal A Signal (not itself a Stop Signal) capable of displaying a Cautionary Aspect, that informs the driver about the state of the next stop Signal ahead. Non-preferred term for a Distant Signal.

Of the above terms, the Rule Book glossary only includes: https://catalogues.rssb.co.uk/rgs/rulebooks/GERT8000-Gloss Iss 5.pdf

Repeater (in a signal box): A dial or indicator in a manual signal box that shows the position of a signal arm and whether the signal lamp is lit.

...which rather proves my point.

 

[Belperpete]

But what happens if I have a sequence when driving of a Stop Signal displaying Yellow then the next signal is a Distant signal-, Could this be also Green or Yellow? Therefore having a possibility of two yellows? Is that possible?

As others have already pointed out, that shouldn't happen. In most cases, you would get a green on the stop signal in rear. What would be the point of providing a yellow aspect on the stop in rear if you are providing a distant with a yellow aspect? It would only make you brake too early.

If the stop signal in rear has several routes, it may have a yellow aspect for its other routes, but it shouldn't display it for the route reading up to the distant signal. It should show green.

In rare cases, you may get a double-yellow on the stop in rear, if there isn't sufficient braking from the distant. But again, why provide a distant that is not at braking distance? This usually only happens in 4 aspect areas, to maintain a consistent aspect sequence. The other situation I have known it, is where you have high-speed and low-speed routes reading toward a stop and distant: the distant provides adequate braking for the low-speed approach, but the high-speed route needs a double-yellow on the signal in rear.

 

[Merle Haggard]

I don't claim to be a signalling expert but I'm a bit confused by how the term 'co-acting signal' is being used.
Where sighting was restricted by, for example, an overbridge a semaphore arm at drivers' eye level would be duplicated by another arm higher up on the same post to give sighting, at a distance, over the obstruction. Both arms were connected and therefore always displayed the same aspect, and this arrangement was called 'co-acting'. I realise that this arrangement is probably extinct being presumably replaced by banner repeaters in the modern world, but there was, for example, one on the Down Fast at Bletchley until power signalling.

 

[driver9000]

I don't claim to be a signalling expert but I'm a bit confused by how the term 'co-acting signal' is being used.
Where sighting was restricted by, for example, an overbridge a semaphore arm at drivers' eye level would be duplicated by another arm higher up on the same post to give sighting, at a distance, over the obstruction. Both arms were connected and therefore always displayed the same aspect, and this arrangement was called 'co-acting'. I realise that this arrangement is probably extinct being presumably replaced by banner repeaters in the modern world, but there was, for example, one on the Down Fast at Bletchley until power signalling.

Co acting signals do exist in colour light TCB areas. Manchester Piccadilly platform 14 and Lancaster (platform 4 and Up Main) have co-acting signals. They work on the same principle as semaphore co-acting signals worked. At Manchester they are slightly off set and at different heights due to the curve of the line and OLE stanchions. At Lancaster one signal is on the ground and the other on a gantry due the over bridge at the south end of the station.

 

[PupCuff]

I don't claim to be a signalling expert but I'm a bit confused by how the term 'co-acting signal' is being used.
Where sighting was restricted by, for example, an overbridge a semaphore arm at drivers' eye level would be duplicated by another arm higher up on the same post to give sighting, at a distance, over the obstruction. Both arms were connected and therefore always displayed the same aspect, and this arrangement was called 'co-acting'. I realise that this arrangement is probably extinct being presumably replaced by banner repeaters in the modern world, but there was, for example, one on the Down Fast at Bletchley until power signalling.

This is indeed the purpose of a co-acting signal, though it does not necessarily have to be on the same post; an example of one not in this arrangement would be the signals placed at the end of the down platforms at East Midlands Parkway where their co-acting signals are adjacent, but on the end of the up platforms due to the curvature of the line.

 

[Merle Haggard]

This is indeed the purpose of a co-acting signal, though it does not necessarily have to be on the same post; an example of one not in this arrangement would be the signals placed at the end of the down platforms at East Midlands Parkway where their co-acting signals are adjacent, but on the end of the up platforms due to the curvature of the line.

Thank you. I had wondered why co-acting on one post had disappeared (because colour lights would presumably have the same sighting problems as semaphores) but you've explained it. 'Sky arms' were always impressive though (but tough for the lamp man!).

 

[edwin_m]

Thank you. I had wondered why co-acting on one post had disappeared (because colour lights would presumably have the same sighting problems as semaphores) but you've explained it. 'Sky arms' were always impressive though (but tough for the lamp man!).

Part of the reason, I think, why colour lights don't need "sky arms" is that the light is visible even against a dark background where the semaphore arm may be hard to pick out until close up to it. If there is no sightline to the signal until the train is very close then as you say a banner repeater is the modern answer.

Another possible reason is that generally a semaphore box will control several stop signals for the same track in the same direction (around its own station limits - we'll leave intermediate blocks out of the discussion). The distant would only clear if all the stop signals were clear, and if a train couldn't go forward to the next box the signaler would have to bring it nearly to a stop at each stop signal before clearing it for the train to draw forward to the next one, and ultimately stop and wait at the section signal.

If during this process the train was accepted forward, the signaler could clear the remaining stop signals but the driver wouldn't know this so would still have to go slowly enough to stop at each one. A sky arm would reduce the delay from this cause, as the driver would be aware sooner that the signal had been cleared. An unofficial way of getting round this problem on mechanical signals was to pull the lever slowly if the next signal was still at danger put pull it off sharply if the section was clear.

 

[Jim Jehosofat]

I don't claim to be a signalling expert but I'm a bit confused by how the term 'co-acting signal' is being used.
Where sighting was restricted by, for example, an overbridge a semaphore arm at drivers' eye level would be duplicated by another arm higher up on the same post to give sighting, at a distance, over the obstruction. Both arms were connected and therefore always displayed the same aspect, and this arrangement was called 'co-acting'. I realise that this arrangement is probably extinct being presumably replaced by banner repeaters in the modern world, but there was, for example, one on the Down Fast at Bletchley until power signalling.

Here's a photo of the co-actor at Thetford in days gone by

Thetford Signal Box 3

Thetford box and co-acting signal number 6 seen on a glorious day with just 9 days of their working lives left. The signal has two arms for sighting purposes. A McKenzie and Holland box of 33 levers built in 1883 working absolute block to Brandon and Harling Road.

www.flickr.com