The first traffic light was gas-powered and erected in London in 1868 and the first 3-colour light
was set up in New York in 1918.
As they spread with the introduction of motorised vehicles, variations on the light sequence
were adopted.
UK
has RED RED-AND-YELLOW GREEN YELLOW which is unambiguous.
Germany
has RED YELLOW GREEN YELLOW with the second YELLOW being longer than the
first.
USA, Spain and Japan
have RED GREEN YELLOW which presumably discourages drivers from jumping the lights.
(I would be grateful for information about other countries.
Please e-mail me, Chris Jakeman)
Road v Rail
Most road traffic lights place the RED at the top where it can more easily be
seen from a distance. In contrast, railway signals place the RED at the
bottom. If it were at the top, the RED could be obscured by snow building up on the hood of
the lamp beneath.
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