Sorry to butt into the convo, but I was a summer intern at a major "traffic light" operation (for lack of a better term) in the southeast (aka, they did all of the traffic lights and systems for the southeast USA). It will seem almost shocking to many here on HN, but the traffic control industry is lagging behind drastically.
I believe the newer systems started going IP based just a few years ago, and (gasp) wireless networking of traffic lights is a really new thing. It has to do with the environment the system must handle and how "tamper-proof" it must be, which leads to hardware and software being waaayy behind the curve.
The main point though, is that it would be very reasonable to think that some hardware, especially if installed before the 90s, wouldn't have "software" to just "turn off monitoring". Even the newer boxes aren't completely controlled by software, they have physical circuitry that operates as a "fall-back" to make sure that things like two green lights on adjacent roads can't be green at the same time, even if the software was hacked, had a bug, etc.