Well, I never saw it in Germany, so I think it's a british thing.
But I can only imagine it being used to mark the locomotive. For the visibility.
You're right...
Imagine being trackside on a warm summer’s morning.
It’s 1952 and there’s hardly a cloud in the sky.
In one direction, you can see for miles as the metals stretch out in front of you; in the other, the line curves away, disappearing down behind a bank lined with trees.
It’s from that direction that the next train’s due.
No problem for you as you work alone in the cess: it’ll probably be worked by a ‘Black Five’ and be audible for miles, the engine barking as it struggles up the gradient – plenty of time to get to a position of safety before it’s upon you.
Now imagine being in the same spot nine years later: it’s still bright, you can still see for miles in one direction and the line still curves away in the other.
The next train’s due from the latter, only this time it’s not a ‘Five’ on the front, but a new-fangled ‘Brush 2’ – a diesel, a demon to some, a necessity to others.
No time to muse on that now, though – you’ve got work to do, and not much time to do it in.
You get stuck in.
You’re so stuck in you almost miss the horn as the train rounds the bend, almost fail to pick up your tools, almost fail to get to a place of safety before it rumbles past...
The trouble was – in comparison to steam engines – diesels were quiet, electrics quieter still.
Yet they had to come, and were coming – though you couldn’t always hear them when they did!
You couldn’t always see them either, the green livery of the diesels often blending them into rural backgrounds.
But what if there was some way they could be made easier to see?
It would certainly help trackworkers, and help farmers using occupation crossings too.
The solution was simple: paint a ‘bright yellow panel’ to the fronts of the new locomotives and units.
From 1961, it was done; it was done a bit more when the new ‘corporate BR identity’ was born a few years later, a full yellow end becoming almost a second livery colour against the cool Monastral Blue of that design.
Did you know that early steam engines in
Germany used a bright red paint on their wheels
to make it easier for safety inspectors to detect metal fatigue and cracks.