This is the kind of thing which crosses into the movie realm. Yes, it is possible to hack traffic lights.
Taking over a city’s intersections and making all the lights green to cause chaos is a pretty bog-standard Evil Techno Bad Guy tactic on TV and in movies, but according to a research team at the University of Michigan, doing it in real life is within the realm of anyone with a laptop and the right kind of radio.
via Researchers find it’s terrifyingly easy to hack traffic lights | Ars Technica.