I've already seen likely malfeasance from the traffic overrides used to help emergency vehicles (in the US) control traffic lights. When the override is activated, a white light turns on near the traffic light. I've seen that go on in heavy traffic when there were no obvious emergency vehicles present.

Another time I was in heavy traffic and held up for about an hour because a parked police car had left their traffic light override turned on, causing the light not to cycle.