A question about Signal indicators.

[MrsCake21]

Hi,

I'm referring to the indicators that are nicknamed a 'feather' indicator with a strip of lights which indicates that you are about to leave the line you are currently on.

Why are these indicators only at some junctions and not all junctions? I was on a train yesterday that didn't have one above the signals, and the train automatically, (signaller would of set it) left the line for another line. Yet further on, we came to a junction and there was a feather about the signal, and it was all lit up and we obviously took that line. The two junctions were identical.

What are the rules and rhymes for the inclusion of an indicator above a signal?
Why are the indicators not at every junction?

Thanks

 

[Supercoss]

Junction indicators can only show three routes to the left or three routes to the right of ‘ straight’ route any more than that a route indicator is provided also known as a theatre box that can display letters or numbers. At some locations a route indicator is provider instead of a junction indicator.

are you able to advise which location and direction you travelled in ?

 

[Boilinthebag]

The key driver of the type of indication provided at junctions is approach speed. Theatre type route indicators are visible from a shorter distance than junction indicators. Even the large type such as at Milton near Didcot are not as easy to see what letter/numbers etc. are displayed, as would be a junction indicator at the kind of distance that is needed for higher speed approaches.

 

[Efini92]

Standards have changed a lot since junction indicators were introduced. So there’s not really one size fits all.
It all comes down to route knowledge for that particular area.

 

[MrsCake21]

Standards have changed a lot since junction indicators were introduced. So there’s not really one size fits all.
It all comes down to route knowledge for that particular area.

Yes I agree, but there must be a reason you use them? Someone said, they are only used when the line you are diverging onto has a drop in speed?

== Doublepost prevention - post automatically merged: 18 May 2025 ==

The key driver of the type of indication provided at junctions is approach speed. Theatre type route indicators are visible from a shorter distance than junction indicators. Even the large type such as at Milton near Didcot are not as easy to see what letter/numbers etc. are displayed, as would be a junction indicator at the kind of distance that is needed for higher speed approaches.

Is it also something to do with the speed of the line you are diverging onto ? I heard when there is a big drop in speed, then they need to put an indicator on the top of the signal to highlight that you are diverging at the next junction. But why if you know the route...?

== Doublepost prevention - post automatically merged: 18 May 2025 ==

Junction indicators can only show three routes to the left or three routes to the right of ‘ straight’ route any more than that a route indicator is provided also known as a theatre box that can display letters or numbers. At some locations a route indicator is provider instead of a junction indicator.

are you able to advise which location and direction you travelled in ?

These were just single diverges, I was more interested in why they have an indicator at some but not others. Someone said it's to do with the line speed you're going onto??

 

[507 001]

Yes I agree, but there must be a reason you use them? Someone said, they are only used when the line you are diverging onto has a drop in speed?

== Doublepost prevention - post automatically merged: 18 May 2025 ==


Is it also something to do with the speed of the line you are diverging onto ? I heard when there is a big drop in speed, then they need to put an indicator on the top of the signal to highlight that you are diverging at the next junction. But why if you know the route...?

== Doublepost prevention - post automatically merged: 18 May 2025 ==


These were just single diverges, I was more interested in why they have an indicator at some but not others. Someone said it's to do with the line speed you're going onto??

Any signal protecting a diverging junction/set of points will have some sort of route indicator, be it a ‘theatre’ type or a ‘feather’ type.

That is unless it is a set of points with only one permissible route, i.e. a single line opening up into a double line.

Theatres are used in relatively low speed areas. PLJIs (feathers) are generally used where line speed is higher.

They are used to indicate to the driver that the correct route for their train has been set.

It would help if we knew exactly where you were talking about so that we could explain the exact set up in that location.

 

[Efini92]

Yes I agree, but there must be a reason you use them? Someone said, they are only used when the line you are diverging onto has a drop in speed?

== Doublepost prevention - post automatically merged: 18 May 2025 ==


Is it also something to do with the speed of the line you are diverging onto ? I heard when there is a big drop in speed, then they need to put an indicator on the top of the signal to highlight that you are diverging at the next junction. But why if you know the route...?

== Doublepost prevention - post automatically merged: 18 May 2025 ==


These were just single diverges, I was more interested in why they have an indicator at some but not others. Someone said it's to do with the line speed you're going onto??

In basic terms they are there to indicate a route. There are places where the different routes that are available are equal speed, so each route has a junction indicator. It really does depend on where you are referring to and how old the installation is.

 

[Supercoss]

Relevant investigation into junction indicator v route indicator from the 2012 Bletchley derailment

Report 24/2012: Derailment at Bletchley Junction

Derailment of locomotive at Bletchley Junction, Bletchley, Buckinghamshire, 3 February 2012.

www.gov.uk

 

[edwin_m]

Any signal protecting a diverging junction/set of points will have some sort of route indicator, be it a ‘theatre’ type or a ‘feather’ type.

That is unless it is a set of points with only one permissible route, i.e. a single line opening up into a double line.

Even then, if the only route available is not the straight ahead route then it will probably still have a junction indicator. That came in after a derailment near Didcot in 1967 when the driver was thought to have momentarily forgotten that the only main route was over low-speed crossovers and straight ahead was into the power station.

 

[Pyewipecarshed]

Junction indicators ("feathers") are normally provided as follows;

- where a diverging route has a lower speed (however if the straight route has the lowest speed the JI will apply to the lower speed (i.e.straight) route).
- Where there is no obvious straight route, in which case all routes would have a JI.
- where all routes are of equal speed, again in which case all routes would have a JI.

As @507 001 says Route Indicators ("theatre boxes") that show letters and/or numbers tend to be used approaching or leaving major stations where speeds are lower and where the number of routes may exceed the limits of JIs.

 

[High Dyke]

Any signal protecting a diverging junction/set of points will have some sort of route indicator, be it a ‘theatre’ type or a ‘feather’ type.

That is unless it is a set of points with only one permissible route, i.e. a single line opening up into a double line.

Theatres are used in relatively low speed areas. PLJIs (feathers) are generally used where line speed is higher.

They are used to indicate to the driver that the correct route for their train has been set.

It would help if we knew exactly where you were talking about so that we could explain the exact set up in that location.

And to add to that. Some goods loops (see Oakham) are route indicated by the white calling-on type lights, no junction or theatre box indicator. However, the driver does get a letter indication (the blue coloured box just below the main signal head.


Image shows a railway signal with two white calling-on lights indicating the route into the Down Goods loop at Oakham. Screenshot taken from the Don Coffey (Peterborough - Birmingham freight train video on YouTube)

 

[NSEWonderer]

And to add to that. Some goods loops (see Oakham) are route indicated by the white calling-on type lights, no junction or theatre box indicator. However, the driver does get a letter indication (the blue coloured box just below the main signal head.

View attachment 180216
Image shows a railway signal with two white calling-on lights indicating the route into the Down Goods loop at Oakham. Screenshot taken from the Don Coffey (Peterborough - Birmingham freight train video on YouTube)

The route indication is the blue coloured box which is a Stencil Indicator box, it usually only provides one indication. White position lights are not indication solely of the Good Loop being set but simply that you must proceed at caution onto the loop which may be occupied hence why you must be able to stop short of any obstruction, train or buffer stops etc in the distance you see to be clear.

 

[MarkyT]

Slower diverging routes are typically approach released from red. Before the junction signal can clear for an approaching train, the driver must be able to clearly see and read the route indication for the divergence so they can regulate speed appropriately. Feather type Junction Indicators can be interpreted reliably much earlier than alphanumeric Route Indicators, so the approach release can occur earlier, further from the signal, keeping trains moving more swiftly and smoothly through the pointwork.

 

[edwin_m]

The route indication is the blue coloured box which is a Stencil Indicator box, it usually only provides one indication. White position lights are not indication solely of the Good Loop being set but simply that you must proceed at caution onto the loop which may be occupied hence why you must be able to stop short of any obstruction, train or buffer stops etc in the distance you see to be clear.

View attachment 180217

The position light may be offset to the left or right below the signal to indicate a divergence in that direction. But more recent installations will indeed have some sort of route indicator. The more modern ones are LEDs which can show multiple indications in the same display.

 

[TSG]

Hi,

I'm referring to the indicators that are nicknamed a 'feather' indicator with a strip of lights which indicates that you are about to leave the line you are currently on.

Why are these indicators only at some junctions and not all junctions? I was on a train yesterday that didn't have one above the signals, and the train automatically, (signaller would of set it) left the line for another line. Yet further on, we came to a junction and there was a feather about the signal, and it was all lit up and we obviously took that line. The two junctions were identical.

What are the rules and rhymes for the inclusion of an indicator above a signal?
Why are the indicators not at every junction?

Thanks

As has been said, factors like speed of approach, number of routes to be displayed and practice at the time of installation. There is usually no indicator if there is no permitted route of course. There is another possible factor. It's not clear how close these junctions were, but rarely would they be identical in every respect, including things like the risks of mis-routing. Occasionally junctions may have a different junction signalling scheme purely to aid the driver in distinguishing a junction within a sequence of junctions. It's not permitted to overlap flashing aspect sequences for exactly that reason for example

 

[MarkyT]

The more modern ones are LEDs which can show multiple indications in the same display.

There have been various technologies used over the years in standard and miniature alphanumeric route indicators.

Before LEDs, fibre optic bundles were used which channelled light from a number of separate lamp chambers within the enclosure to a front plate with a fine matrix of holes. The fibre ends of each bundle were arranged in the matrix to depict the desired character(s). Not as flexible as LEDs, but it was an earlier way to display a number of different route indications in the same box. The technique could also be used for banner repeaters, OFF and RA indicators etc using the same basic unit.

Going further back, multiple alphanumeric indications were even possible in mechanical semaphore installations using a series of movable stencils in front of a light box.

Another tech popular for the larger 'standard' route indicators in the 1960s was a dot matrix arrangement using incandescent lamps, These were fiendishly complicated devices and very expensive.

The colloquial term 'theatre' indicator for the large type came from music hall variety theatre, where a display was often provided facing the audience showing a number corresponding to the current act as detailed in the programme.

 

[sharpener]

The colloquial term 'theatre' indicator for the large type came from music hall variety theatre, where a display was often provided facing the audience showing a number corresponding to the current act as detailed in the programm

Well blow me down. I have often wondered about the name's origins, and I have a long-standing interest in theatre lighting as well but have never heard it before.

So thank you for that @MarkyT. Doesn't say a lot about the distinctiveness of the acts does it!

 

[Annetts key]

Although officially, Network Rail (or was it Railtrack) dropped the term 'theatre' indicator some time ago...

The current terms are "Alphanumerical Route Indicators", then sub divided into Standard Alphanumerical Route Indicators (SARI) and Miniature Alphanumerical Route Indicators (MARI).

A filament or fibre optic 'theatre' is now classed as a SARI.

A "stencil" is now called a MARI.

Just for the record, the official name for a "feather" is Position Light Junction Indicator or PLJI, often shortened to JI.

 

[swt_passenger]

Is the up direction signal at Reading West relatively unusual in that for some routes it uses a PLJI and SARI at the same time?



== Doublepost prevention - post automatically merged: 22 May 2025 ==

Well blow me down. I have often wondered about the name's origins, and I have a long-standing interest in theatre lighting as well but have never heard it before.

So thank you for that @MarkyT. Doesn't say a lot about the distinctiveness of the acts does it!

Likewise, I could never quite see a use in a theatre. But thanks to the earlier pointer I found this definition using Google:

ACT NUMBER INDICATOR
An indicator board visible to the audience on the proscenium arch of a theatre used for variety performances which showed the Act Number so the audience could tell who was on stage (after referring to their printed programme).
One type of board used replaceable numbers which were replaced by hand, another type used a paper scroll containing the numbers which was advanced either mechanically or electrically. The most popular type used an array of light bulbs which were illuminated in patterns to depict the numbers.

Glossary of Technical Theatre Terms – The Theatre Building – Theatrecrafts.com

www.theatrecrafts.com

 

[MarkyT]

Is the up direction signal at Reading West relatively unusual in that for some routes it uses a PLJI and SARI at the same time?

I think it's rare and quite a modern innovation, so expect it may be a feature in other modern layouts of the last decade or so. The idea is that a single PLJI position seen first can apply to a series of destinations all turning off in the same direction and having the same or very similar speed characteristics, so there's no danger of misjudging approach speed. The SARI then details the precise destination when it resolves into readability a little later. The arrangement can apply for entry to a group of similar bays diverging from a through line, as at Reading for example.

Well blow me down. I have often wondered about the name's origins, and I have a long-standing interest in theatre lighting as well but have never heard it before.

So thank you for that @MarkyT. Doesn't say a lot about the distinctiveness of the acts does it!

The explanation came from old timers in the WR Reading signalling drawing office when I was a young trainee in the 1980s. There was a lot of time to fill!

Likewise, I could never quite see a use in a theatre. But thanks to the earlier pointer I found this definition using Google
"...The most popular type used an array of light bulbs which were illuminated in patterns to depict the numbers."

So a dot matrix of incandescent lamps, just like the early railway route indicators. I recall fairly sophisticated lamp proving arrangements to prevent a potentially dangerous mangled display from misleading drivers.

 

[Cross Fell]

Junction indicators ("feathers") are normally provided as follows;

- where a diverging route has a lower speed (however if the straight route has the lowest speed the JI will apply to the lower speed (i.e.straight) route).
- Where there is no obvious straight route, in which case all routes would have a JI.
- where all routes are of equal speed, again in which case all routes would have a JI.

I noticed a while ago that the junction indicators for Wolverhampton North Junction on the down, and for Bushbury Junction on the up, appear to be anomalous in this. In both cases it is the higher speed route, the present main line, which physically diverges from the lower speed route and yet the higher speed route has a feather indicator. Wolverhampton North in the Down direction is 35/45 mph for the Shrewsbury line and 60mph for the diverging Bushbury/Stafford line, yet it is the Bushbury route that has a feather. Similarly, Bushbury Junction in the Up direction is 20mph for the Grand Junction line but 60mph for the diverging Wolverhampton route, yet the Wolverhampton direction has the feather.

I have wondered if this is related to the historical precedence of the routes as much as to the geographical arrangements. The Shrewsbury and Birmingham Railway (which never got beyond Wolverhampton) and the Grand Junction Railway were the two original lines in this area, and despite its subsequent importance the LNWR Wolverhampton to Bushbury link only came several years later. I don't know how they were signalled in mechanical days but would welcome any enlightenment on what seems like inversion of the usual indicator priorities.