Signalling Trivia - Warnham to Horsham.

[Deepgreen]

While watching a video I took in April 2024 of a steam working leaving Warnham for Horsham, I noticed something that I hadn't previously. The southbound starting signal at Warnham was cleared and the train departed, and the next signal south (four aspect) was showing green. As the train passed that signal, it turned to double-yellow rather than red. Now, was this because the signaller re-set the route ahead, or was it some form of semi-automatic signal that would normally show double-yellow rather than red when passed?

If the latter, I don't think I have come across this before with four aspect signalling. If the former, that would mean that the driver, having seen green and expecting either a green or a double-yellow next, would actually probably see single yellow. The route is not a fast one, but I find it odd for a driver potentially to be faced with an unexpected aspect in this way.

Just curious, if anyone has the explanation.

 

[bramling]

While watching a video I took in April 2024 of a steam working leaving Warnham for Horsham, I noticed something that I hadn't previously. The southbound starting signal at Warnham was cleared and the train departed, and the next signal south (four aspect) was showing green. As the train passed that signal, it turned to double-yellow rather than red. Now, was this because the signaller re-set the route ahead, or was it some form of semi-automatic signal that would normally show double-yellow rather than red when passed?

If the latter, I don't think I have come across this before with four aspect signalling. If the former, that would mean that the driver, having seen green and expecting either a green or a double-yellow next, would actually probably see single yellow. The route is not a fast one, but I find it odd for a driver potentially to be faced with an unexpected aspect in this way.

Just curious, if anyone has the explanation.

The first signal south of Warnham is not a stop signal. As is usual practice it will change to its most restrictive aspect when a train passes, which in this case would seem to be YY.

 

[zwk500]

If the former, that would mean that the driver, having seen green and expecting either a green or a double-yellow next, would actually probably see single yellow.

If the signal in rear is not capable of showing red, the signal in rear of the Distant signal (T831 in this instance) will be held at red until the section is clear to the next signal capable of showing red (presumably T837)*. So the driver won't see the Double Yellow out of Sequence.

* - I'm sure there's an exception somewhere.

 

[godfreycomplex]

There’s quite a few of these floating about, they’re known as Double Repeater or Outer Distant signals. There’s another one country side of Horsham, coming from Christ’s Hospital on the Up. Other locations include Blea Moor and various bi-di installations

 

[Deepgreen]

Many thanks - after 50+ years of railway interest, there's always something new to learn!

== Doublepost prevention - post automatically merged: 27 Aug 2025 ==

The first signal south of Warnham is not a stop signal. As is usual practice it will change to its most restrictive aspect when a train passes, which in this case would seem to be YY.

Many thanks - so it is actually only a three aspect (no red) but as part of the four aspect system?

 

[merry]

- so it is actually only a three aspect (no red) but as part of the four aspect system?

Strictly, no. A three aspect signal has the ability to display red, yellow or green.
As a previous poster stated, this is a colour light outer distant. The next signal is no more restrictive than yellow when this displays double yellow.
In a TC block area like this, the signal can only show double yellow or green. In this context, green means next signal can only be green or double yellow (or single yellow if transitioning to a 3 aspect area). Double yellow means next will be no more restrictive than yellow. Yellow means next signal could be red, or something less restrictive.
In an Absolute Block area it would be slightly different: if there is an outer distant, it can show green, double of single yellow. The next signal will not be more than one aspect more restrictive, but if an AB outer distant is green, all signals controlled by that box will be clear as the next section is clear.
Yes, sounds complicated, but it isn't really.

 

[Deepgreen]

Strictly, no. A three aspect signal has the ability to display red, yellow or green.
As a previous poster stated, this is a colour light outer distant. The next signal is no more restrictive than yellow when this displays double yellow.
In a TC block area like this, the signal can only show double yellow or green. In this context, green means next signal can only be green or double yellow (or single yellow if transitioning to a 3 aspect area). Double yellow means next will be no more restrictive than yellow. Yellow means next signal could be red, or something less restrictive.
In an Absolute Block area it would be slightly different: if there is an outer distant, it can show green, double of single yellow. The next signal will not be more than one aspect more restrictive, but if an AB outer distant is green, all signals controlled by that box will be clear as the next section is clear.
Yes, sounds complicated, but it isn't really.

Indeed, got it - my clumsy wording - I meant a signal able to display three different aspects only - i.e. no red (a three lamp signal if you will), but it turns out it can only show two aspects - YY or G. Does it have a bulb at all where the red would be? All minor stuff I know, but it was a new one on me. Thanks.

 

[zwk500]

Does it have a bulb at all where the red would be? All minor stuff I know, but it was a new one on me. Thanks.

Not normally, I think. You might get a 4-Aspect head with the normal red aspect location plated over, or a 3-Aspect head with just Yellow-Green-Yellow bulbs.

 

[swt_passenger]

Not normally, I think. You might get a 4-Aspect head with the normal red aspect location plated over, or a 3-Aspect head with just Yellow-Green-Yellow bulbs.

Then with LEDs could it be two ‘light units’#, with one yellow only and the other green or yellow?

# (I’m not sure if there’s an agreed terminology now, when a single light unit can display up to 3 colours, I think some people use searchlight but to me that’s a completely different technology.)

 

[zwk500]

Then with LEDs could it be two ‘light units’#, with one yellow only and the other green or yellow?

# (I’m not sure if there’s an agreed terminology now, when a single light unit can display up to 3 colours, I think some people use searchlight but to me that’s a completely different technology.)

I think so yes, but it wouldn't look any different on first inspection to a standard 2-apeture* LED Signal capable of displaying All 4 Aspects.

* Apeture seems to be the terminology used by at least one manufacturer: https://www.unipartdorman.co.uk/technical-documents/#trackside

 

[Deepgreen]

Thanks to all - fascinating stuff, and interesting to learn that there are two of these relatively rare signal units in the Horsham area.

 

[devon_belle]

I saw this thread a while ago but had nothing to add. However it's come back into my mind so I had a look at some info I was sent a while back about the signalling on this stretch.

After Warnham's starting signal T831 (red/green) there are two repeaters, T833 and T835 (both 3 bulb yellow/green/yellow, but with a blanked out 4th bulb).

Similarly, on the approach to Dorking from Horsham there is CBK41RR (3 bulb yellow/green/yellow) and CBK41R (2 LED, yellow/green & yellow, I think).

It seems quite arcane, and also confusingly inconsistent between the Dorking end and the Horsham end. Are the Warnham-Horsham ones also considerred 'repeater repeater' and 'repeater', despite the difference in naming?

Some pictures: