Junction(route) indicator "incorrectly described"

MisterW · 21 Mar 2024

Dear all,

Many years back in our original driver training (UK mainline railway) we were told that when presented with a junction route indicator arm, pre LED type with five white lights, that if two or more of the white lights in the indicator arm had failed that the route should be considered "incorrectly described" and not taken, contact the signaller and act upon the instructions given.

I cannot for the life of me find anywhere in any available publications if this was EVER was an official rule or was and has been since dropped and whether there are any such restrictions currently in place.

Can anyone shed any light on this?

For clarity:
1) Was the two or more lamps failed in the junction indicator arm to be considered "incorrectly described" a rule?
2) Is there a current rule (there's nothing in the latest RSSB rulebook) or guide in effect that relates to the number of failed indicator lamps there can be in the suction indicator before it must be considered not showing correctly?

Your input and assistance gratefully appreciated!

RailUK Forums

Lucy1501 · 21 Mar 2024

In terms of signalling equipment, the route indicators should illuminate before the signal clears. This is to allow the route indicator to be proved, and if it isn’t proved to be lit, the signal won’t clear.

There is some logic to determine if the route indicator’s display has been affected enough by failure, so one or two lamps out might not be enough to hold the signal at danger.

Theoretically if a driver is unsure of a route indication they should stop and question it. TOCs can add their own defensive driving rules as they see fit even if it’s not in the rulebook.

Ashley Hill · 21 Mar 2024

Nothing wrong with reporting it as defective,but as above if you’re unsure if the correct route is displayed then stop and question.

Annetts key · 21 Mar 2024

Lamp type position light junction indicators (often called "feathers") as said above illuminate before the signal aspect changes to a proceed aspect. For the five lamp types, the lamp proving circuit (where provided) should detect if three or more lamps are lit. If this is the case, the signal should clear to a proceed aspect. Otherwise it will stay red. The signaller will normally notice this before a driver.

If a driver notices a problem with a signal, the driver should report the defect or problem to the signaller. Drivers often report a problem to the signaller when one lamp is unlit.

357 · 21 Mar 2024

I was taught to report one bulb out at the first convenience but if two or more are out to stop the train and report it.

Leyland155 · 21 Mar 2024

As you say, at my TOC we're instructed that a junction indicator must display at least three lights (referred to as Lunar Lights) for the route to be accepted. But it should be reported regardless of how many bulbs have failed. I do wonder how this works with the new VMS-type bar junction indicators, thought I suppose it's more likely that the entire light bar would fail rather than a specific section.

Railsigns · 21 Mar 2024

Leyland155 said:
I do wonder how this works with the new VMS-type bar junction indicators, thought I suppose it's more likely that the entire light bar would fail rather than a specific section.

Individual LED failures are not unknown...

[Photo of a VMS LED junction indicator with some LEDs unlit]

Annetts key · 21 Mar 2024

Leyland155 said:
As you say, at my TOC we're instructed that a junction indicator must display at least three lights (referred to as Lunar Lights) for the route to be accepted. But it should be reported regardless of how many bulbs have failed. I do wonder how this works with the new VMS-type bar junction indicators, thought I suppose it's more likely that the entire light bar would fail rather than a specific section.

Modern LED types have various failure modes, depending on the design. Some fail completely, some may fail and show one, two, three, or four 'lights'.

Leyland155 · 21 Mar 2024

Railsigns said:
Individual LED failures are not unknown...
[Photo of a VMS LED junction indicator with some LEDs unlit

Fortunately I've not come across one in that state yet!

Annetts key said:
Modern LED types have various failure modes, depending on the design. Some fail completely, some may fail and show one, two, three, or four 'lights'.

I see, it's strange that there isn't a universal standard with the failure mode.

MadMac · 21 Mar 2024

The “rule“ in terms of functionality and engineering was that you needed four lit to clear the signal but if another one failed while the signal was cleared, it would stay cleared. I don’t recall ever seeing anything mentioned rules-wise.

Annetts key · 22 Mar 2024

Leyland155 said:
I see, it's strange that there isn't a universal standard with the failure mode.

Each manufacturer has developed and makes their product independently. As long as they comply with the Network Rail specification and have gained product acceptance they can be used on Network Rail infrastructure. So, exactly how they work varies between manufacturers. Hence they have various failure modes.

The Doman Junction Indicator types are designed to look similar to the conventional lamp type. And use modules. So a failure of a single module is possible leaving part of the Junction Indicator working.

See https://www.unipartdorman.co.uk/route-indicators/

It is also possible for the current proving system to fail, the driver will still see the signal lit. But the interlocking will not.

And just for the record, even conventional lamp type signals had various failure modes. With position light junction indicators the most common problem with the type in our area was with the lamp contacts. Hence one or more lamps may intermittently light up or not, sometimes flashing on or off if vibration or wind caused the signal to move slightly.

Two different lamp types could be used in some designs. This also caused problems in that with one failure mode, a one lamp type would light at half brightness. During sunny weather conditions, the lamp may not look lit to a driver, but the lamp proving system may still consider the lamp lit. Modifications were therefore supposed to be carried out to the affected heads.

Hence with both of these failure modes, different train drivers may see a different number of lamps lit...

Leyland155 · 22 Mar 2024

All very interesting, thank you for that detailed reply!

Annetts key said:
Each manufacturer has developed and makes their product independently. As long as they comply with the Network Rail specification and have gained product acceptance they can be used on Network Rail infrastructure. So, exactly how they work varies between manufacturers. Hence they have various failure modes.

The Doman Junction Indicator types are designed to look similar to the conventional lamp type. And use modules. So a failure of a single module is possible leaving part of the Junction Indicator working.

See https://www.unipartdorman.co.uk/route-indicators/

It is also possible for the current proving system to fail, the driver will still see the signal lit. But the interlocking will not.

And just for the record, even conventional lamp type signals had various failure modes. With position light junction indicators the most common problem with the type in our area was with the lamp contacts. Hence one or more lamps may intermittently light up or not, sometimes flashing on or off if vibration or wind caused the signal to move slightly.

Two different lamp types could be used in some designs. This also caused problems in that with one failure mode, a one lamp type would light at half brightness. During sunny weather conditions, the lamp may not look lit to a driver, but the lamp proving system may still consider the lamp lit. Modifications were therefore supposed to be carried out to the affected heads.

Hence with both of these failure modes, different train drivers may see a different number of lamps lit...

All very interesting, thank you for that detailed reply!

Chris Hamilton · 25 Mar 2024

In a relay based signalling environment with filament lamps:

Three lamps (including the pivot - the lamp shared amongst all routes) are required to be lit for the signal to show any sort of proceed aspect. The circuit is current sensitive, and the route lamp proving relay (UECR) has contacts in the circuit for the yellow aspect. If the UECR drops because of a fall in the current draw (i.e., two lamps already failed and another gives up the ghost as the train is about to pass), it will drop the relay controlling the yellow aspect (HR), which will return the signal to danger. Even if the route is already set up, which has the potential to result in a SPAD.

That is why most if not all TOCs treat two lamps out as a “stop and report” event. Of course, that may not always be possible, especially if the feather is being used at a high speed turnout following flashing yellows. It’s also incredibly rare for a filament to fail once lit, as we all know, it’s when you flick the switch, the bulb blows.

Much like the main aspects, there are LED replacements for the filament lamps, but unlike the main aspects (which are now mostly LED lamps), we haven’t ever changed any feathers to LED (at least in the parts of Scotland I’ve worked in).

I can’t speak for the procedure for newer LED matrix feathers such as the one shown above, as there are none on my section.

Junction(route) indicator "incorrectly described"

MisterW

New Member

RailUK Forums

Lucy1501

Member

Ashley Hill

Established Member

Annetts key

Established Member

357

Established Member

Leyland155

Member

Railsigns

Established Member

Annetts key

Established Member

Leyland155

Member

MadMac

Member

Annetts key

Established Member

Leyland155

Member

Chris Hamilton

Member