London Underground signals with route indicators

[1018509]

Why did - or perhaps - still do - route indicators have the top two lights joined by a plate?

[class411]

Isn't the real question why the top two are separated from the bottom one?

Also, what is the exact purpose of the shrouds?

I can think of three reasons, but none of them seem particularly likely. Since there is no shrouding to the right, shielding the lights from drivers on adjacent tracks (as the shrouding on the red and green) does not seem that likely.

[rincew1nd]

There is no "shrouding to the right" of the main aspects, there are however pig's ears which help the train operator see the aspect when drawn up to the signal.

[class411]

Feb 7, 2021 20:58:35 GMT rincew1nd said:

There is no "shrouding to the right" of the main aspects, there are however pig's ears which help the train operator see the aspect when drawn up to the signal.

By 'shrouding', I meant the 'collars' (I don't know what the technical term for them is), that are fitted to signals, road and rail. They are open at the bottom so that snow cannot build up on them.

[Chris M]

Certainly with road traffic signals these are "hoods" and are there primarily to aid visibility in bright light and prevent sunlight giving false aspects.
Whatever their name none of this answer's the OP's question about why 2 of three junction indicator lights share one but the third doesn't.

[1018509]

I don't know where the pictured location is but when I worked at Rayners Lane 1973 - 2002 both platform SB starters had them fitted. I asked the question then and no one knew.

[zbang]

Do all three light up together, or lower and center+upper? I could see hood/shroud/pig's-ear on a pair that are supposed to always operate together; gives a hint to the operator that they're a single indication.

That is, of course a complete WAG. There might be something in one of my signalling books, but no time to check this week.

[Tom]

Yes, they all light up together. However, if there were to be two diverging routes, the lowest lamp will need to light for both of them (known as the pivot lamp) and then you can't join the hood to the other two.

[philthetube]

Feb 7, 2021 23:50:52 GMT Tom said:

Yes, they all light up together. However, if there were to be two diverging routes, the lowest lamp will need to light for both of them (known as the pivot lamp) and then you can't join the hood to the other two.

you probably have the answer there, the extended hood may be to ensure that there can be no mistake seeing which route is illuminated on a diverging signal, and it is just a standard part used on signals with only one set of harbour lights.

Having said this some signals with one set of lights do have separate hoods

When I did my training I was taught that these are harbour light signals.

[class411]

Feb 8, 2021 7:47:47 GMT philthetube said:

Feb 7, 2021 23:50:52 GMT Tom said:

Yes, they all light up together. However, if there were to be two diverging routes, the lowest lamp will need to light for both of them (known as the pivot lamp) and then you can't join the hood to the other two.

you probably have the answer there, the extended hood may be to ensure that there can be no mistake seeing which route is illuminated on a diverging signal, and it is just a standard part used on signals with only one set of harbour lights.

Having said this some signals with one set of lights do have separate hoods

When I did my training I was taught that these are harbour light signals.

Can you say something about 'harbour lights' as they apply to railways. I found them mentioned here but it wasn't very helpful.

Surely something that was literally a miniature harbour light would be too easy to mistake for a normal signal (at some distances).

[Dstock7080]

Feb 8, 2021 9:44:23 GMT class411 said:

Can you say something about 'harbour lights' as they apply to railways. I found them mentioned here but it wasn't very helpful.

Surely something that was literally a miniature harbour light would be too easy to mistake for a normal signal (at some distances).

Delving back into the archives, I found this thread:
districtdavesforum.co.uk/thread/1483/arbor-arbour-harbour

Dec 5, 2005 17:23:00 GMT Dstock7080 said:

A 'Point of Interest' article in the current UNDERGROUND NEWS (LURS house magazine) says:

"References in previous issues and elsewhere have perpetuated the misheld belief that the slang term for a Junction Route Indicator are 'Harbour lights'. However, the real term is ARBOR lights.
To explain its origin, Arbor is the Latin term for 'branch'- your local tree surgeon is an arboriculturalist!"

Well, thats taught me something!!

[Tom]

Feb 8, 2021 7:47:47 GMT philthetube said:

you probably have the answer there, the extended hood may be to ensure that there can be no mistake seeing which route is illuminated on a diverging signal, and it is just a standard part used on signals with only one set of harbour lights.

Having said this some signals with one set of lights do have separate hoods

When I did my training I was taught that these are harbour light signals.

It's as much down to the age of the signal head and when the mechanical design was produced. The arrangement in this thread is the standard Westinghouse design for a three-lamp junction indicator, there were other designs for ones manufactured by LT and provided from other suppliers such as Howells or Metropolitan-Vickers/AEI/GRS.

[philthetube]

Couple of asides on these.

If 2 of the white lights fail on a given route, then the signal will fail, (Remain at danger)

I am told that the colour of the writes is actually Lunar white.

[Deleted]

Not strictly true it requires 3 filaments to light in a outside type signal like the one in the original post. On a tunnel type it requires at least 2 lamps to make the signal clear as they are only single filament lamps.

On a outside type signal junction indicator each lamp has 2 filaments.

If you see the junction lights on with a red aspect yes the signal is failing but only requires a quick relamp of the defective lamps.

They are known as lunar white as the lens is actually blue in colour

[t697]

Still using filament lamps in route indicators? Presumably not included in the project to change over to LEDs a few years ago?

[Deleted]

LED’s do work in them but a modification needs to be made to the circuit but the powers that be didnt like the idea so we are still using lamps in junction indicators.

[zbang]

(More for my own curiosity than anything else.)

Is that due to watching the lamp current to know that they're lit? Since LEDs draw a fraction of what incandescent lamps do, that relay won't trigger.

There's also the possibility that a circuit is using the filament as a ballast resistor and LED replacements don't behave like that.

[Deleted]

Outside lamps are 33.5W and tunnel lamps are 5W

LED’s that work are 3W behaving like a tunnel lamp

[class411]

Feb 11, 2021 21:05:03 GMT zbang said:

(More for my own curiosity than anything else.)

Is that due to watching the lamp current to know that they're lit? Since LEDs draw a fraction of what incandescent lamps do, that relay won't trigger.

There's also the possibility that a circuit is using the filament as a ballast resistor and LED replacements don't behave like that.

I was wondering that.

The failure mode of an LED may well not be as clear cut as that of an incandescent bulb.

[Deleted]

The LED’s LU was using were designed to fail short circuit

[1018509]

I think the answer to my original question has appeared here. Without the hoods on the top two lamps if there were two or more diverging routes the lamps that were not lit could pick up a reflection from the ones that are. The fact that the route indicators I have seen just happen to have only one route that needs indicating. What is not needed is confusion in signalling.

[Deleted]

Also the pivot light at the bottom has a seperate casing for the lamps then the other two

[roythebus]

There's also a reason for the red aspect being at the bottom of the signal. Remember there was a tragic crash on the Brighton Line in 1977/78 when a main line express collided with the one in front during snow. The cause was the red aspect had been obscured by snow building up on the shroud of the aspect below it. the Brighton line signals were amongst the first used on the former Southern Railway and had the red light 2nd from the bottom.

I read elsewhere that the term is "arbor lights" for route indicators as the Latin term. I always thought it was harbour lights!

[spsmiler]

Feb 22, 2021 7:49:30 GMT roythebus said:

There's also a reason for the red aspect being at the bottom of the signal. Remember there was a tragic crash on the Brighton Line in 1977/78 when a main line express collided with the one in front during snow. The cause was the red aspect had been obscured by snow building up on the shroud of the aspect below it. the Brighton line signals were amongst the first used on the former Southern Railway and had the red light 2nd from the bottom.

I read elsewhere that the term is "arbor lights" for route indicators as the Latin term. I always thought it was harbour lights!    

Signals on the Great Eastern Main Line out of Liverpool Street station used to be like that - red one up from the bottom. Somewhere I have a photo showing this.

I do not have a photo of a LU combined stop and distant signal, these have 4 aspects with the stop signal using the top two aspects and the distant signal using the lower two aspects. I recall seeing one (maybe even several) of these just outside of Leyton station, many years ago - as eastbound trains exit the tunnel they encounter a sharp right-hand curve before arriving at Leyton station and in the days before the line was resignalled for automation I used to be able to see these signals whilst enjoying a driver's eye view of the route ahead.

Usually I would see two green lamps (ie: both home and distant), but sometimes the home was green and the distant was yellow / amber, and occasionally solely the home signal lamp was illuminated - and red.

The combined signals here actually comprised two twin-aspect signal heads slightly staggered in a way which I suppose was designed to ensure that a build-up of snow would not block the view of the red.

[DWS]

Feb 22, 2021 18:42:24 GMT spsmiler said:

Feb 22, 2021 7:49:30 GMT roythebus said:

There's also a reason for the red aspect being at the bottom of the signal. Remember there was a tragic crash on the Brighton Line in 1977/78 when a main line express collided with the one in front during snow. The cause was the red aspect had been obscured by snow building up on the shroud of the aspect below it. the Brighton line signals were amongst the first used on the former Southern Railway and had the red light 2nd from the bottom.

I read elsewhere that the term is "arbor lights" for route indicators as the Latin term. I always thought it was harbour lights!    

Signals on the Great Eastern Main Line out of Liverpool Street station used to be like that - read one up from the bottom. Somewhere I have a photo showing this.

I do not have a photo of a LU combined stop and distant signal, these have 4 aspects with the stop signal using the top two aspects and the distant signal using the lower two aspects. I recall seeing one (maybe even several) of these just outside of Leyton station, many years ago - as eastbound trains exit the tunnel they encounter a sharp right-hand curve before arriving at Leyton station and in the days before the line was resignalled for automation I used to be able enjoy a driver's eye view of the route ahead.

Usually I would see two green lamps (ie: both home and distant), but sometimes the home was green and the distant was yellow, and occasionally solely the home signal lamp was illuminated - and red.

The combined signals here actually comprised two twin-aspect signal heads slightly staggered in a way which I suppose was designed to ensure that a build-up of snow would not block the view of the red.

London Underground does not have colour light distant signals the signal you noticed with two green lights was a stop signal and a repeater signal .

[brigham]

Feb 22, 2021 19:13:28 GMT DWS said:

London Underground does not have colour light distant signals the signal you noticed with two green lights was a stop signal and a repeater signal .

Although I believe that only the NAME is different, the principle being the same.

[bomo]

Feb 22, 2021 7:49:30 GMT roythebus said:

There's also a reason for the red aspect being at the bottom of the signal. Remember there was a tragic crash on the Brighton Line in 1977/78 when a main line express collided with the one in front during snow. The cause was the red aspect had been obscured by snow building up on the shroud of the aspect below it. the Brighton line signals were amongst the first used on the former Southern Railway and had the red light 2nd from the bottom.

I read elsewhere that the term is "arbor lights" for route indicators as the Latin term. I always thought it was harbour lights!

The Patcham accident was not caused by snow.  It was caused by the total failure of the red aspect lamp resulting in the signal being dark with a train in advance of it.   Also the colour light signals installed by the Southern Railway between Coulsdon North and Brighton as part of the Brighton electrification project, including the signal that failed resulting in the accident, had the red aspect at the bottom.