Rail gap indicator?

[trebor79]

Whilst waiting for a westbound train at Aldgate East today, I noticed a curious signal and wonder what it is/was?
At the end of the platform is a triangular signal with 3 lenses on it. There's a placard attached which says "Rail Gap Ind."

What is it and what does it indicate?

 

[Tubeboy]

Traction current on the underground is divided into sections.

Before each current section there is a white triangular rail gap indicator. Prior to this indicator this there is a yellow triangular indicator, which is a rail gap indicator repeater, which is an advance warning that the current is off. If the three lights on it are illuminated, it indicates that the traction current section ahead is off. Normally only illuminated in engineering hours or if there is a need to discharge current during traffic hours, eg an operating incident, so a service can be still provided on other sections.

 

[Mojo]

Further to the reply above, the purpose of the Rail Gap Indicator is for train operators to know that the section ahead is switched off, and not to proceed any further (without authority).

Prior to this indicator this there is a yellow triangular indicator, which is a rail gap indicator repeater, which is an advance warning that the current is off.

Only where there is insufficient sighting time for the actual indicator to be seen is there a repeater. Without looking at every diagram I’d probably say there is a significant number /without/ repeaters.

 

[trebor79]

Thanks.

 

[Lewlew]

Without looking at every diagram I’d probably say there is a significant number /without/ repeaters.

Just the one repeater on the Bakerloo (at Oxford Circus)

 

[Dieseldriver]

If a train passes an illuminated Rail Gap Indicator it counts as a SPAD (Signal Passed At Danger). There is a potential danger of livening up the dead section if a train traverses the rail gap from a live section into a dead section.

 

[Ex LT]

If a train passes an illuminated Rail Gap Indicator it counts as a SPAD (Signal Passed At Danger). There is a potential danger of livening up the dead section if a train traverses the rail gap from a live section into a dead section.

Even if it lights up just as you get to it? I seem to remember being taught if you can't stop in time to shut off and coast into the next section.

== Doublepost prevention - post automatically merged: 15 Dec 2021 ==

Just the one repeater on the Bakerloo (at Oxford Circus)

I thought there was more but on checking there are 31 RGIs and like you say 1 RGIR.

 

[Dieseldriver]

Even if it lights up just as you get to it? I seem to remember being taught if you can't stop in time to shut off and coast into the next section.

== Doublepost prevention - post automatically merged: 15 Dec 2021 ==


I thought there was more but on checking there are 31 RGIs and like you say 1 RGIR.

As far as I’m aware, if a train passes it when it illuminates suddenly with no time to stop, it’s treated as a technical SPAD. If it was illuminated the whole time then it’s the equivalent of a Cat A SPAD.
Like you say, if you are unable to stop at it in time the instruction is to shut off and coast through it for as long as you can to get the train all the way into the dead section to prevent it bridging the rail gap.

 

[trebor79]

Surprised there are only 32 of them on the network. There are surely more than 32 sections?

 

[Lewlew]

Surprised there are only 32 of them on the network. There are surely more than 32 sections?

I think it's 32 on the Bakerloo

 

[bramling]

As far as I’m aware, if a train passes it when it illuminates suddenly with no time to stop, it’s treated as a technical SPAD. If it was illuminated the whole time then it’s the equivalent of a Cat A SPAD.
Like you say, if you are unable to stop at it in time the instruction is to shut off and coast through it for as long as you can to get the train all the way into the dead section to prevent it bridging the rail gap.

Yes, however the sighting of many indicators isn’t always perfect, so passing one can be a can of worms opened. Fortunately it’s pretty rare to happen.

 

[REVUpminster]

Rail Gap indicators are not normally lit (like Fog Repeaters) the white plate tells the driver not to treat it as signal with no aspect. Ones in stations can be activated if station staff use the section ahead plunger. The headwall tunnel telephone only discharged current to the rear of the telephone. The section ahead plunger might be used if a passenger disappeared down a tunnel. That's how it worked in my day.

 

[Dstock7080]

Rail Gap indicators are not normally lit (like Fog Repeaters) the white plate tells the driver not to treat it as signal with no aspect.

Fog repeaters have been required to be on at all times for some years now, as SPAD mitigation.

 

[Ex LT]

I think it's 32 on the Bakerloo

Thanks I should have said Bakerloo adding another line after checking my notes on the Northern there are 118 RGIs and 2 RGIR.

 

[philthetube]

As far as I’m aware, if a train passes it when it illuminates suddenly with no time to stop, it’s treated as a technical SPAD. If it was illuminated the whole time then it’s the equivalent of a Cat A SPAD.
Like you say, if you are unable to stop at it in time the instruction is to shut off and coast through it for as long as you can to get the train all the way into the dead section to prevent it bridging the rail gap.

This is correct although as far as I am aware thee are no short rail gaps anymore and so trains cannot actually bridge them.