Can 3 lens signals display preliminary caution?

[DistantAR3]

I always imagine the top and bottom lenses would display yellow, but I've never seen an example of a 3 lens showing pre caution.

 

[The Planner]

I always imagine the top and bottom lenses would display yellow, but I've never seen an example of a 3 lens showing pre caution.

What do you mean by pre caution? Double yellow? It can be done on a transition to four aspect signalling where a 3 aspect signal head has yellow, green, yellow. You can't have a double yellow on three aspect signalling, or it would be four aspect.

 

[rheingold103]

Or on a stop signal that shows maximum double yellow (preliminary caution). Top lens Y, middle R, bottom Y to give R-Y-YY.

 

[DistantAR3]

What do you mean by pre caution? Double yellow? It can be done on a transition to four aspect signalling where a 3 aspect signal head has yellow, green, yellow. You can't have a double yellow on three aspect signalling, or it would be four aspect.

I mean I know 3 lenses can show red, yellow and green but can they also show double yellow as well as those three.

 

[The Planner]

I mean I know 3 lenses can show red, yellow and green but can they also show double yellow as well as those three.

I'm not sure what you are getting at? Most modern LED signals have two signal lenses that can show different aspects in a 4 aspect area, a single lens in 3 aspect. A historic 3 lens bulb signal wouldn't be able to do what you are suggesting.

 

[DistantAR3]

I'm not sure what you are getting at? Most modern LED signals have two signal lenses that can show different aspects in a 4 aspect area, a single lens in 3 aspect. A historic 3 lens bulb signal wouldn't be able to do what you are suggesting.

I mean would a 3 lens LED signal (if they exist) show 4 aspects

 

[John Webb]

I mean would a 3 lens LED signal (if they exist) show 4 aspects

They - a three-lens LED signal - don't exist as far as I am aware.
A Single LED 'Module' is usually capable of showing three aspects: Red, Yellow and Green one at a time.
So these are used in three-aspect signal areas.

A second module, wired to show only a yellow aspect, is placed above the fully working module to give the preliminary Y-Y signal in four-aspect areas.

 

[edwin_m]

I mean I know 3 lenses can show red, yellow and green but can they also show double yellow as well as those three.

With "traditional" multi-lens signals each lens can only show one colour. A three-lens one would nearly always be green-yellow-red but yellow-green-yellow would appear occasionally as mentioned in #2 above. I guess yellow-red-yellow is theoretically possible but usually red needs to be nearest the driver so they would probably just use a four-aspect and block off the one that would normally be green.

Many years ago there were distant signals with two yellow lenses, with one being a backup in case the other one failed. These were superseded by dual-filament lamps. There were also distant signals that could display double yellow as an early form of warning for a diverging route or crossover, mainly by the LMS I think. Either of these would probably have had yellow-green-yellow lenses in that order.

 

[DistantAR3]

They - a three-lens LED signal - don't exist as far as I am aware.
A Single LED 'Module' is usually capable of showing three aspects: Red, Yellow and Green one at a time.
So these are used in three-aspect signal areas.

A second module, wired to show only a yellow aspect, is placed above the fully working module to give the preliminary Y-Y signal in four-aspect areas.

ah, thanks a lot.

 

[4COR]

On the approaches to London Victoria, on Grosvenor Railway Bridge, I seem to recall from the distant past three aspect signals with Y-R-Y, leading up to R-Y as the final signal before platform. Am I misremembering?

 

[Taunton]

Traditional Searchlight signals, more on the ex-LNER than anywhere else, for example Liverpool Street to Shenfield, could have two lenses. Bottom one showed R/Y/G like a 3-aspect, upper one only lit Y in combination with the lower Y, to give a 4-aspect double yellow.

USA, where these signals originated from, commonly had two vertically mounted multi-colour lenses (and sometimes three), but their approach to signalling and what is shown is completely different.

 

[GW43125]

On the approaches to London Victoria, on Grosvenor Railway Bridge, I seem to recall from the distant past three aspect signals with Y-R-Y, leading up to R-Y as the final signal before platform. Am I misremembering?

No, you remember correctly.
Similar installations survive (or at least did three weeks ago) on the approach to Liverpool Street.

 

[alxndr]

They - a three-lens LED signal - don't exist as far as I am aware.

You can have signals where the filament lamps have been replaced by LED light engines. It’s just a direct swap from filament lamp to light engines, so they work in exactly the same way as the filament lamps did, but lit by LEDs.

 

[Annetts key]

The variations of filament lamp heads that I have seen include:

• 3 aspect head that can only show red or green (middle aspect blanked out)
• 3 aspect head that can only show red or yellow (top aspect blanked out)
• 3 aspect head that can only show single yellow or double yellow (middle aspect blanked out)
• 4 aspect head that normally only shows single yellow, double yellow or green (only shows red when an emergency switch is operated)

 

[4COR]

No, you remember correctly.
Similar installations survive (or at least did three weeks ago) on the approach to Liverpool Street.

My memory isn't so bad then!

Here's a cab ride video from 1990 (Horsham - Victoria) showing the Y-R-Y signals (at 1:04:06).

EDIT: Here's a slightly more modern (but pre-LED replacements) - a Gatwick to Victoria cab ride, VC536 at 32:30:

 

[PLY2AYS]

I was always under the impression that historically, the lowest aspect had to be a Red, to prevent build up of snow on the hood of the signal below blocking the most restrictive aspect…

Happy to concede that this may be a railway fairytale, but genuinely curious if anyone knows if that holds any truth.

Obviously now we have modern LEDs capable of multiple colour light aspects, this seems a redundant feature.

 

[Annetts key]

I was always under the impression that historically, the lowest aspect had to be a Red, to prevent build up of snow on the hood of the signal below blocking the most restrictive aspect…

Happy to concede that this may be a railway fairytale, but genuinely curious if anyone knows if that holds any truth.

Obviously now we have modern LEDs capable of multiple colour light aspects, this seems a redundant feature.

The main objective is to have the red aspect as near to the drivers eye line as possible. That's why the most restrictive aspect is normally at the bottom for post, bracket or gantry signals.

Wet sticky snow tends to accumulate on all the lenses of all aspects. If trains are regularly passing, the air flow from the trains does help to remove some snow if it is the dry powdery type.

 

[edwin_m]

The main objective is to have the red aspect as near to the drivers eye line as possible. That's why the most restrictive aspect is normally at the bottom for post, bracket or gantry signals.

Wet sticky snow tends to accumulate on all the lenses of all aspects. If trains are regularly passing, the air flow from the trains does help to remove some snow if it is the dry powdery type.

A signal mounted below driver's eye level has the red at the top, confirming this factor is more important than any snow buildup. But the Y-R-Y signals mentioned in previous posts don't follow this "rule" - are they in some limited space where a four-aspect with the green blanked out wouldn't fit?

 

[PLY2AYS]

The main objective is to have the red aspect as near to the drivers eye line as possible. That's why the most restrictive aspect is normally at the bottom for post, bracket or gantry signals.

Makes perfect sense, thanks for clarifying!

 

[D6130]

A signal mounted below driver's eye level has the red at the top, confirming this factor is more important than any snow buildup. But the Y-R-Y signals mentioned in previous posts don't follow this "rule" - are they in some limited space where a four-aspect with the green blanked out wouldn't fit?

Y-R-Y signals - such as those on the approach to Victoria and other terminal stations - had to have the red aspect between the two yellows to give the degree of separation required to prevent the two yellows from appearing to merge into one when seen from a distance.

 

[Snow1964]

On the approaches to London Victoria, on Grosvenor Railway Bridge, I seem to recall from the distant past three aspect signals with Y-R-Y, leading up to R-Y as the final signal before platform. Am I misremembering?

A few locations like this approaching a terminus, in 4 aspect areas.
Cannot show green, as there isn't three sections beyond the signal.

There have been (not sure if any still exist) three aspect distants, (yellow, green, yellow, with no red) Lymington Junction used to have one approaching from Sway (Christchurch to Lymington Junction was 2 aspect with home signals about every three miles from 1967 until resignalling few years ago). Approach to Brockenhurst gained a single 4 aspect (remainder were 3 aspect) when resignalled in 1978 (probably due to platform loops followed by a level crossing) and the preceding signal was 2 aspect about 3 miles before, this was before the flashing junction signals were introduced.

 

[edwin_m]

Y-R-Y signals - such as those on the approach to Victoria and other terminal stations - had to have the red aspect between the two yellows to give the degree of separation required to prevent the two yellows from appearing to merge into one when seen from a distance.

As I posted already, unless there's some space or sighting constraint, they could equally well have the red at the bottom and just be a normal four-aspect but having the green blanked out so the yellows are separated. I'm curious why a Y-R-Y was adopted in these places, contrary to general practice on positioning of the red.

 

[John Webb]

As I posted already, unless there's some space or sighting constraint, they could equally well have the red at the bottom and just be a normal four-aspect but having the green blanked out so the yellows are separated. I'm curious why a Y-R-Y was adopted in these places, contrary to general practice on positioning of the red.

Could it be that as it is approaching a terminus the overall train speeds are lower than on more open line and therefore sighting of the red is easier?

 

[D6130]

Could it be that as it is approaching a terminus the overall train speeds are lower than on more open line and therefore sighting of the red is easier?

IIRC, the 'outer home' signals at Victoria were/are positioned a short way down the steep falling gradient beyond the level section over the Grosvenor Bridge, this rendering a normally-positioned red aspect difficult to see within the prescribed braking distance.

 

[4COR]

IIRC, the 'outer home' signals at Victoria were/are positioned a short way down the steep falling gradient beyond the level section over the Grosvenor Bridge, this rendering a normally-positioned red aspect difficult to see within the prescribed braking distance.

From the route video above, they actually look to be on the level (or at least were) - they were positioned right on the join between the river bridge and the bridge over Grosvenor Rd before the falling gradient into the terminus.

 

[satisnek]

From memory (which can't be relied upon) the penultimate signal on the approach to Eastbourne was, from top to bottom, Y-[blank]-Y-R. The final signal was, of course, Y-R with a route indicator. That was how things were when the panel installed c1990 was in use - I don't know what there was before when the signals were worked from the lever frame, or what there is today.

I thought that 3-aspect (Y-G-Y) distant signals were as common as muck - after all, there are four of them on the preserved GCR alone. Weren't they used, in conjunction with a conventional 3-aspect (G-Y-R) outer home signal, where services terminated so that trains weren't checked at the outer home? There used to be such an arrangement at Kidderminster.

 

[NSEWonderer]

I was always under the impression that historically, the lowest aspect had to be a Red, to prevent build up of snow on the hood of the signal below blocking the most restrictive aspect…

Happy to concede that this may be a railway fairytale, but genuinely curious if anyone knows if that holds any truth.

Obviously now we have modern LEDs capable of multiple colour light aspects, this seems a redundant feature.

Co Acting signals have the red on the top due to their height if that counts.

 

[edwin_m]

I thought that 3-aspect (Y-G-Y) distant signals were as common as muck - after all, there are four of them on the preserved GCR alone. Weren't they used, in conjunction with a conventional 3-aspect (G-Y-R) outer home signal, where services terminated so that trains weren't checked at the outer home? There used to be such an arrangement at Kidderminster.

This could be one or other of the types I mentioned in a previous post - either the yellow is a spare or it gives advance warning of a diversion, or perhaps it could be termination? But I can't say which or if they might be something else entirely, maybe indicating the home is clear but the starter isn't?

Co Acting signals have the red on the top due to their height if that counts.

The majority do that are mounted low down, but if one is mounted at normal height it will have the red at the bottom. There are some at East Midlands Parkway which look just like normal signals but on the "wrong" side of the double track.

 

[izvor]

Traditional Searchlight signals, more on the ex-LNER than anywhere else, for example Liverpool Street to Shenfield, could have two lenses. Bottom one showed R/Y/G like a 3-aspect, upper one only lit Y in combination with the lower Y, to give a 4-aspect double yellow.

I remember these on the LTSR. I was so intrigued by these as a boy that I took a photo of all 4 aspects. When the black & white prints came back...

As a matter of interest, did these have 3 different coloured bulbs, or moveable lenses? If the latter, was there some sort of failsafe to prevent a green (or yellow) lens getting stuck and showing a false clear?

 

[John Webb]

I remember these on the LTSR. I was so intrigued by these as a boy that I took a photo of all 4 aspects. When the black & white prints came back...

As a matter of interest, did these have 3 different coloured bulbs, or moveable lenses? If the latter, was there some sort of failsafe to prevent a green (or yellow) lens getting stuck and showing a false clear?

The 'searchlight' signals had a swinging frame between the bulb and the lens containing three colour filters. The frame by weight and springs was normally in a central position showing red. A solenoid moved the frame in either direction to give the yellow or green aspects - when unpowered the frame moved back to the 'red' position.