I’m in New York. In my city, the police make the final determination, and the camera provides context of the situation when the camera detects a light running event.
The police also use them as a time indexed source of evidence that can help stitch a timeline of events filmed on random security cameras. I know because they presented that in a case I was a juror on.
Ah, that makes sense. it sounds like there's one benefit to having the cameras rolling (that the police can apply judgment before red-light tickets are handed out) but another detriment (that the cameras are rolling 24/7. Seems you could obtain the same benefit by having a 2-min cache running at all times, and only store the cache permanently when a light-running event is triggered.
That said, we do have a lot of "traffic cameras" mounted on poles, which presumably do record 24/7 and are archived for some period of time.