This is very interesting. I looked around a bit and according to OED: “Another word used in South Africa, but long discontinued in England, is robot for traffic lights.” (reference). Looking around a bit more: “It makes sense in its own way: It's a device that replaces a policeman directing traffic.” (reference)
"The etymology of the word derives from a description of early traffic lights as robot policemen, which then got truncated with time." (Wikipedia)
It's actually quite logical; the problem (or humour) arises because South Africa is the only country where this term is used. Older readers will remember that, until ~1970, it was still common for road junctions in the UK to be controlled by bored-looking policemen.