"Fred Johnson" wrote in message
news
On Thu, 13 Dec 2018 21:03:57 -0000, Mike Humphrey
wrote:

Fred Johnson wrote:

Can anybody else remember blue traffic lights on railways? Can't find
any evidence on google. I'm sure whereas cars have red/amber/green,
railways always had a 4th blue light. What does it mean and why has it
disappeared from Google?

Railway signals in modern times have always had red, yellow (not
amber)

I've never been fussy enough to even notice the difference between yellow,
amber, orange. I could tell the difference if they were side by side, but
I just think of a road traffic light as either yellow or orange. I
couldn't even tell you what amber colour is compared to yellow and orange.
I don't do things like "mauve", etc. Just purple, light purple, etc.

and green. A four-aspect signal has two yellows - the sequence
approaching a stop signal goes G, YY, Y, R. There can be a number of
other indications as well as the main signal but these are almost
invariably white.

I assume this is to allow trains the longer stopping distance they require
than road vehicles.

There's a number of uses for blue and purple, but not appearing with the
R/Y/G "traffic light" signals, at least in the UK.

I might be thinking of non "traffic light" signals, or I might be thinking
of a light which was off and was just seeing the blue lens which had a
yellow light behind to make green.

If you want to look
at the full range of signs and signals, http://www.railsigns.uk/ has a
very comprehensive guide.

That's a lot for a driver to remember! At least with road signs the
symbol is meaningful.

I wonder why the red is at the bottom on rail lights and the top on
traffic lights?

Basically because when there are two ways of doing
something, you can be sure someone will do it both ways.