Atomic Systems

transadelaide wrote:This is uninformed.

2 aspect signals DO exist, and don't need the previous signal to show just green/yellow. They are only used in slower-speed locations like station approaches or chokepoints on the network where bi-directional working may be needed (like the Forth Bridge) where the speed is slow enough that the driver can stop at the next signal without needing a yellow aspect...

Can you give some examples, in Britain please, as that statement seems to contradict that by a current driver in this thread.

Andy L

AndyUK wrote:

transadelaide wrote:This is uninformed.

2 aspect signals DO exist, and don't need the previous signal to show just green/yellow. They are only used in slower-speed locations like station approaches or chokepoints on the network where bi-directional working may be needed (like the Forth Bridge) where the speed is slow enough that the driver can stop at the next signal without needing a yellow aspect...

Can you give some examples, in Britain please, as that statement seems to contradict that by a current driver in this thread.

Andy L

On the approaches to London Paddington!

Andy, I'm not sure how things work between Marylebone and Amersham with the LUL side of things but this isn't regular mainline running at that most drivers would be used to. We have an ex-Chiltern driver at my depot so I shall enquire about the operations on that stretch.

Thanks, very kind of you.

Andy L

transadelaide wrote:

AndyUK wrote:If the signals are set up to only show red or green then no, that's not how it is on the real railway despite what whoever set up the signalling on the approaches to Paddington in the default route might think!

You can have signals only capable of showing two colours but in that case they would be arranged so that before a signal that can only show red or green there would be one capable of showing green or yellow so that the driver would get a caution signal before a stop signal, much like how it's done on a semaphore signalling installation.

Modern LED type signals can show more than one colour from the same 'lens' so four aspect signalling will have signal heads that look like two aspect ones

This is uninformed.

2 aspect signals DO exist, and don't need the previous signal to show just green/yellow. They are only used in slower-speed locations like station approaches or chokepoints on the network where bi-directional working may be needed (like the Forth Bridge) where the speed is slow enough that the driver can stop at the next signal without needing a yellow aspect. For the driver it means that they have to approach the following signal at a speed that allows them to stop if it shows a red aspect when it is finally seen, something that a repeater helps make more convenient.

A cab video I just found on YouTube (uploaded in 2007) confirms this is appropriate, the signals coming onto the bridge from either end are 2 aspect colour light signals (they are NOT clustered LED signals either) present.

http://www.youtube.com/watch?v=XLvSWDgYCu8

If I'm correct, I believe repeaters are usually the white disc type as seen on WCML North, indicating either red or not red.

If you pause the video you will find the signal coming off the bridge is a 3 aspect, the signal before it showing green is actually a distant signal that shows either green or yellow. I have driven over this bridge hundreds of times so I am quite familiar with it. The incorrect signalling here was one of the things I found disappointing, signal spacing in some places was another. As far as I am aware LU is the only company in Britain that uses 2 aspect signals without distants, and even they use repeaters of a unique style for foggy weather or limited vision. If I remember correctly they don't use them if speed is above 40 mph, but LU have their own unique signalling and rules. As far as I remember the joint LU/Chiltern lines were signalled to BR standards, at least until the late 90's anyway. There are several styles of repeater on BR and they are not classed as stop signals
Edit: the joint lines also had trip-cocks integrated as well IIRC, no aws on LU stock.

There's a signaling diagram available for the whole route on Mully's SECML web site, which includes signal IDs too.

Indeed there is and it confirms what I typed above.

It's been a while since I studied signalling but any signal that can display a red aspect must be proceeded by a signal that can display amber. this applies to 2 aspects signals to, a red/green signal must have an amber/green signal proceeding(distant sig)

AndyUK wrote:
But having re-read coolhand101's post I'm confused. Can a repeater show red or will it show yellow if the signal it's the repeater for is red?

Andy L

Sorry for any confusion. When I say the repeater will inform the driver if the next signal is red, then the repeater will show a yellow aspect. If the repeater is displayingi a green aspect, then the next signal will be displaying a proceed aspect, either green, two yellows or one yellow.

Thanks

coolhand101 wrote:

AndyUK wrote:
But having re-read coolhand101's post I'm confused. Can a repeater show red or will it show yellow if the signal it's the repeater for is red?

Andy L

Sorry for any confusion. When I say the repeater will inform the driver if the next signal is red, then the repeater will show a yellow aspect. If the repeater is displayingi a green aspect, then the next signal will be displaying a proceed aspect, either green, two yellows or one yellow.

Thanks

What you are describing as a repeater is actually a distant signal. There are various forms of repeaters used by BR, where sighting is poor, mechanical and LED, they almost all take the form of a black bar on a white disk or LED equivalent. When the bar is horizontal the next signal is on, when at 45% it is off. There are also platform repeaters which simply say off, and are intended to let station staff know when it is ok to send off the train. These are additional to and not instead of normal signals.

A very interesting thread!
Modern signalling is becoming an unknown area for me! On my own routes I always stick to the principles of the old fashioned 'absolute block' whether using semaphores or the various colour light signals.
Our privatised railway system seems to have been split up, not only in physical terms, but also in the official terminology used. As I understand it the USA railroads used their signals in slightly different ways from each other. Are our rail companies heading in the same direction, staff employed by one company using terms and references that do not necessarily apply to another company?
regards Ted.

holzroller wrote:
What you are describing as a repeater is actually a distant signal. There are various forms of repeaters used by BR, where sighting is poor, mechanical and LED, they almost all take the form of a black bar on a white disk or LED equivalent. When the bar is horizontal the next signal is on, when at 45% it is off. There are also platform repeaters which simply say off, and are intended to let station staff know when it is ok to send off the train. These are additional to and not instead of normal signals.

Ally (pacerpilot) has earlier in this thread described the differences between a repeater and distant colour light signal

holzroller wrote:As far as I am aware LU is the only company in Britain that uses 2 aspect signals without distants

There used to be 2 aspect red / green signals on the Merseyrail network also (in the original Mersey Railway tunnels) however I think these were replaced by standard 3 aspect signals when the tunnels were resignalled in the 90s.

FoggyMorning wrote:
Ally (pacerpilot) has earlier in this thread described the differences between a repeater and distant colour light signal

Then either terminology has changed or it was a case of old habits die hard, probably the latter now I come to think of it, we always referred to these signals as distant's, same with the ones coming into TCB areas. It was 16 years ago. Regardless the last two aspect signal on the bridge going north should be Green/Yellow not Red/Yellow.

holzroller wrote:

coolhand101 wrote:

AndyUK wrote:
But having re-read coolhand101's post I'm confused. Can a repeater show red or will it show yellow if the signal it's the repeater for is red?

Andy L

Sorry for any confusion. When I say the repeater will inform the driver if the next signal is red, then the repeater will show a yellow aspect. If the repeater is displayingi a green aspect, then the next signal will be displaying a proceed aspect, either green, two yellows or one yellow.

Thanks

What you are describing as a repeater is actually a distant signal. There are various forms of repeaters used by BR, where sighting is poor, mechanical and LED, they almost all take the form of a black bar on a white disk or LED equivalent. When the bar is horizontal the next signal is on, when at 45% it is off. There are also platform repeaters which simply say off, and are intended to let station staff know when it is ok to send off the train. These are additional to and not instead of normal signals.

No no. Even though it's already been explained, you can get colour light repeaters and color light distant signals. The CL repeaters i've seen are from ABB to TCB or very long block sections with infrequent traffic. As mention above, the colour light repeater will have the same number prefix as the colour light signal which has a danger aspect but will have a R next to the prefix number, ie WH14 for the colour light stop signal, and WH14R for the repeater colour signal. If the stop signal has poor sighting, then a banner repeater will normally be associated with that signal and will have the prefix of WH14BR.
I believe the "BR" prefix for the banner repeater and the "white triangle" for the distant are post BR as before this, i never recalled a distant signal, colour or semaphore having a prefix plate but i could be wrong there.
Back to the above route, does this mean there are some incorrect placed signals?
Thanks