I would wonder if something like that actually happened - it might have been an unfamiliar trick of the light or electrical malfunction...

It's entirely possible. I recall I stayed at that intersection for a few minutes, watching the light and trying to figure out how such a thing might have happened, before concluding I had hallucinated it - but I can't make any guarantees that I was very thorough, given my mental state at the time. I don't think an electrical malfunction would have produced what I saw, but a trick of the light is plausible.