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Neil P

Two aspect colour light signalling - no space for distant

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On lines that are signalled with two-aspect colour lights, could someone explain what happens if there isn't space for a distant signal between two home signals? For example, a junction protected by a signal a hundred yards before a station with a starter signal at the end of the platform?

 

Would they use a three aspect for the signal protecting the junction? 

 

Apologies if I've got any terminology wrong, as this is new to me. Reason I'm asking is to keep the costs down, I'm keen to use two aspect signalling on my layout (1980s). I'll pretend that most of the distant signals are off-scene, but I'm stumped with what to do with a branch line that joins the mainline just before the station.

 

Thanks,

Neil

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Yes it would be a three aspect, not uncommon where a semaphore layout has been modernised piecemeal. 

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On some schemes dating from the 70s on the WR, and probably elsewhere, 2 aspect signalling was used on the method of every other signal having yellow and green aspects, interspersed with red and green.  This meant that a red aspect could be preceded by a yellow, and the yellow preceded by a green.  The Swansea extension to Port Talbot Panel was of this sort as was a stretch of the Badminton cut off signalled for two way working in connection with the introduction of the HST timetable.

 

 In this case the yellow/green signal is in effect the 'distant', though to be pedantic that term does not apply to MAS signalling, and neither does 'home' or 'starter'.   On MAS (multiple aspect signalling) each signal that can display a red aspect is effectively a block signal in it's own right, allowing clearance only as far as the next such signal.  Signals on MAS schemes are controlled from the Panel, or automatic, controlled on stretches of plain main line by passage of the trains by the track circuits.  Such signals are identified by a white oblong plate on the post with a black bar through it.  Automatic signals that can be controlled from the panel by an override are 'semi automatic', and the word 'semi' is printed on the white plate above the black bar.  All MAS signals have push button telephones connecting to the Panel Box; they are called Signalling Centres nowadays.  

 

The other sort of two aspect signal you could still come across was the colour light distant of a semaphore Signal Box, yellow and green aspects.  Distant signals were often replaced with colour lights at manual boxes because the quarter mile plus of wire to pull was physically tough on the signalman and needed heavy maintenance to be operable at all.  The signal was to be read in the same way as a semaphore distant is read at night.

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Thanks @The Johnster

 

Presumably this scheme of alternating red-green yellow-green two aspect signals is still used on some mainlines today (or at least was in the late 1980s)?

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I doubt that it would be a new installation on mainlines today because three aspect signalling, which can display a red aspect on each signal, is more flexible and provides more capacity for running trains.  However, I understand that two aspect signalling still exists across many parts of the network, particularly on lightly trafficked secondary lines, where the existing semaphores were almost replaced like for like with colour light signals in a piecemeal basis.  If there is no need to increase the line capacity, then there is no need to update the signalling and what was installed many years ago can remain.  There are even a few semaphore signals left on the rail network.

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10 hours ago, The Johnster said:

In this case the yellow/green signal is in effect the 'distant', though to be pedantic that term does not apply to MAS signalling, and neither does 'home' or 'starter'.   On MAS (multiple aspect signalling) each signal that can display a red aspect is effectively a block signal in it's own right, allowing clearance only as far as the next such signal.  Signals on MAS schemes are controlled from the Panel, or automatic, controlled on stretches of plain main line by passage of the trains by the track circuits.  Such signals are identified by a white oblong plate on the post with a black bar through it.  Automatic signals that can be controlled from the panel by an override are 'semi automatic', and the word 'semi' is printed on the white plate above the black bar.  All MAS signals have push button telephones connecting to the Panel Box; they are called Signalling Centres nowadays.  

As an aside, "distant" has come back into favour for colour lights and is now preferred over the older term "repeater" for a signal with no red aspect.  Such signals now display a black plate with a white triangle and don't have phones.  

1 hour ago, Neil P said:

Thanks @The Johnster

 

Presumably this scheme of alternating red-green yellow-green two aspect signals is still used on some mainlines today (or at least was in the late 1980s)?

 

3 minutes ago, Dungrange said:

I doubt that it would be a new installation on mainlines today because three aspect signalling, which can display a red aspect on each signal, is more flexible and provides more capacity for running trains.  However, I understand that two aspect signalling still exists across many parts of the network, particularly on lightly trafficked secondary lines, where the existing semaphores were almost replaced like for like with colour light signals in a piecemeal basis.  If there is no need to increase the line capacity, then there is no need to update the signalling and what was installed many years ago can remain.  There are even a few semaphore signals left on the rail network.

If the distance from the R/G signal to the Y/G signal is similar to that from the Y/G to the next R/G then indeed there seems little reason just to make them all three-aspects.  However with a two-aspect scheme the distance from the R/G to the Y/G is unlimited, but from a Y/G to a R/G is limited to (from memory) the maximum braking distance for the line speed and gradient plus 50%.  This is to reduce the risk of a driver passing a yellow, not needing to brake immediately and forgetting they have done so until they see the red.  So in low density areas this form of signaling is still appropriate.  The "modular signaling" schemes done in recent years have concentrated signaling in "islands" which generally replicate the old semaphore boxes.  Each of which has a Y/G distant unless close enough to the previous one to make it a three-aspect.  

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Hopefully without confusing the OP too much, the Leeds - Harrogate line starts off as 4 aspect colour lights at Leeds, becomes 3 aspect up to Horsforth, and is 2 aspect with Y/G distants from there to the outskirts of Harrogate. The 2 aspect stretch replaces two block sections and effectively turns them into 4 (?) signal sections to double the line capacity. The signals themselves are a mixture of old 1960s filament lamps which look like they were hewn from solid steel and the new modular Tupperware signals on the 2 aspect bit. Beyond Harrogate you enter the Museum of Edwardian Signalling - single line electric token block with semaphores and intermediate crossing keepers, before rejoining the 21st century at York. 

 

And some modellers think signalling is boring !

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Some bits round Hastings have just had the old semaphores replaced with....new semaphores! Why? Because of overlaps and the like which do not comply with latest standards. It was easier to replace like-with like.

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If you're going to have a YG distant followed by 3 aspect then RG 2 aspect, the thing to watch out for is braking distances. There needs to be breaking distance between each signal.

 

I'm guessing the 3 aspect junction to 2 aspect station starter is shorter than braking distance? If so then you need the distant to be Y when the station starter is R and have the middle signal R stepping up to Y on approach.

 

Modern versions of this problem may be solved by having a very short 4 aspect sequence.

 

Will

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46 minutes ago, WillCav said:

I'm guessing the 3 aspect junction to 2 aspect station starter is shorter than braking distance? If so then you need the distant to be Y when the station starter is R and have the middle signal R stepping up to Y on approach.


Thanks. Luckily I’m using JMRI for control so I’m pretty sure I can put some rules in there once I have block detection working. 
 

I’m treading a fine line between fun and realism, as I’m building a “train set” for me and my sons to enjoy, but I can’t quite bring  myself to make something that wouldn’t be vaguely plausible in the prototype. 

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3 hours ago, WillCav said:

If you're going to have a YG distant followed by 3 aspect then RG 2 aspect, the thing to watch out for is braking distances. There needs to be breaking distance between each signal.

 

I'm guessing the 3 aspect junction to 2 aspect station starter is shorter than braking distance? If so then you need the distant to be Y when the station starter is R and have the middle signal R stepping up to Y on approach.

 

Modern versions of this problem may be solved by having a very short 4 aspect sequence.

 

Will

 

There are two separate situations here.

a.  Where a R/Y/G colour light has replaced the home signal and a R/G colour light has replaced the starter in a traditional setup.  You have full braking distance from the distant to the home and the home can only be cleared with the starter at danger when a train has slowed right down ready to stop at it.  Then you don't need full braking distance from home to starter.

b.  In every other situation you need full braking distance between each pair of signals in a Y/G, R/Y/G, R/G set up

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9 hours ago, Neil P said:

Thanks @The Johnster

 

Presumably this scheme of alternating red-green yellow-green two aspect signals is still used on some mainlines today (or at least was in the late 1980s)?

Possibly but a lot of it vanished from the WR  in a reasonably short time because HMRI would not permit it to be used on routes where the line speed exceeded 100mph so virtually all the WR 2 aspect stretches west of Wootton Bassett had to be converted to multiple aspect signals for the introduction of HSTs and increased line speeds.  The only exceptions were where SIMBIDS was installed in stead of full Reversible signalling and 2  (and 3) aspect repeaters were allowed in a limited number of locations - but not all  of that was commissioned on the Badminton route although some of the signals stood there for years and were only removed when the route was resignalled for electrification.

 

There was also some 2 aspect signalling on the Swindon - Gloucester section of double line between Kemble and Standish Jcn where it effectively almost recreated the block sections as they were at the time of resignalling.   Similarly there is some between Bathampton and Bradford Jcn and on parts of the mainline between Newton Abbot & Plymouth and between Castle Cary and Cogload although some of that is a mixture of 2 & 3  aspect signals..   Two aspect has been used because it saves money and allows much longer sections but it reduces line capacity compared with continuous multiple aspect signalling due to far longer distances between signals capable of showing a red aspect.

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