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Overview
In railway signalling, a distant signal (British English) or approach signal (US English) is a signal that repeats the aspects of a signal some distance ahead. Railway signalling is a safety system used on railways to prevent trains from colliding. ...
A signal may refer to: an abstract element of information, or, more exactly, usually a flow of information (in either one or several dimensions). ...
Trains travelling at any significant speed require hundreds if not thousands of metres to stop, and by the time that an obstruction is reached it will be too late to stop.
It is therefore necessary to have a home signal at the obstruction, and a Distant signal located at at least braking distance on the approach side.
Shapes and colours British Semaphore Distant Signal Distant signals vary around the world, in shape, colour, coloured lights at night, and how they work.
The most common arangement is a semaphore arm painted yellow with a black stripe to facilitate sighting, which shows a yellow light in the warning position, and a green light in the clear position.
The distant signal has a fishtail shape to distinguish it from a Home signal.
The yellow colour (used since 1922) is a good colour for warnings. Yellow is the color of light whose wavelength is between 565 nm and 590 nm, or is a mixture of red and green light that appears to be the same color. ...
The black "V" on the arm is to help recognise the signal when the background is an unsuitable colour, for example, a fir tree that turns yellow when it flowers. If a suitable background cannot be provided, an artificial one would need to be provided.
The distant signal shows a yellow lamp in the caution position and a green lamp in the clear position. Yellow is the color of light whose wavelength is between 565 nm and 590 nm, or is a mixture of red and green light that appears to be the same color. ...
Wiktionary has a definition of: Green Green is a colour seen commonly in nature. ...
Norway 
- Next Home signal clear.
- Y = Yellow (unlit)
- FG = Flashing Green (lit)
See Also
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