From: ajw@squid.mel.dit.CSIRO.AU (Andrew Waugh)
Newsgroups: rec.railroad
Subject: Re: Signal type (was: Re: Semaphore Signals)
Date: 13 Oct 92 06:04:32 GMT
Organization: CSIRO, Division of Information Technology, Melbourne

In article <1992Oct09.123310.28008@x.co.uk> clive@x.co.uk (Clive Feather) writes:
>In article <1992Sep2.005414.19229@mailhost.ocs.mq.edu.au> eoliver@laurel.ocs.mq.edu.au (Eddie Oliver) writes:
>Secondly, in most layouts (particularly in the UK), the distance from
>stop signal to the next distant is much longer than the distance from
>the distant to the stop, and so there is much more likely to be a train
>before the distant (where adding a danger aspect would not help) than
>after (where it would). Thus such a change is probably not cost-effective.

If a block is occupied the most likely place to find the train is waiting
for a clear signal at the exit of the block!

In any case, Eddie is not talking about retrofitting a danger position to
an existing distant signal, but 'new' installations. While not providing
for a distant (really a repeater) to show stop does simplify the design
a little it is more dangerous.

>This route also had interesting junction distant signals:
>
>        G                       Y                       Y   
>        |     Straight          |     Right-hand        |     Left-hand
>     O--+--O  ahead          Y--+--O  diverging      O--+--Y  diverging
>        |     route             |     route             |     route
>        O     clear             Y     clear             Y     clear
>        |                       |                       |   
>        |                       |                       |   

This may not be exactly correct, although this is what is contained in
Kichenside & Allen. The Railway Gazette of May 12, 1933 which described the
Euston to Watford widening says:

	This is the stop signal for Bushey, BE 1, with the directional
	indicators which advise how the junction is made at Colne
	junction. When CJ 1 [the junction signal] is at yellow or
	green for Croxley Green junction direction [the high speed route],
	BE 1 exhibits green and the right-hand side lamp displays a
	yellow light. If BJ 1 [typo? should be CJ 1] is at yellow or
	green for the High Speed direction [the diverging route which
	diverges to the right], BE 1 exhibits a double yellow over red
	vertically and the left-hand side lamp displays a yellow light.
	This signifies "Attention, pass next signal at restricted speed."

        G                       Y               
        |     Straight          |     Right-hand
     O--+--Y  ahead          Y--+--O  diverging 
        |     route             |     route     
        O     clear             Y     clear     
        |                       |               
        |                       |               

The 'odd' yellow light is quite straightforward -- think of it as a bracket
signal:

Route Straight ahead                Route set diverging

	+---O         +---G                +---Y         +---R
     |--+-O---G    |--+                 |--+-Y---Y    |--+    
        +---Y         +-R                  +---O         +-G
-----------------------------       ------------------\--------------
                      \                                \
                       \                                \
                        \                                \

The only odd thing is that the 'double yellow' for the diverging route
appears to be for the high speed route.

andrew waugh