Steve Walker wrote:
It matter for railways due to needing to determine the colour from a
long distance, due to the long stopping distance of a train. It is fine
for a colourblind person to drive a car, as the stopping distance is
short enough for the driver to get close enough to determint the
position of the light on traffic light.

Perhaps more importantly, road signals are two-aspect. Anything that's
not green means stop - if you're close enough to worry about whether
it's amber or red, you're close enough to see if it's the middle or top
light. Also the "green" is actually a blue-green, there's enough blue in
it to make a very clear contrast with red, even for people with
red-green colour-blindness (like me).
Other signals also have non-colour cues - for example the motorway
warning signs flash amber up and down for a warning, but red
side-to-side for a lane or road closure.

On the railways, you need to distinguish yellow (stop at the next
signal) from red (stop here) in the dark, rain, snow or fog, while
travelling at 100mph or more. Perfect colour vision is mandatory to work
on the railway.

Mike