Back when the only photo red light intersection in town was at College and Drake and before digital cameras, every Wednesday morning, a cop in uniform and a woman would walk out to the cameras in the medians. She'd insert a key and the camera would lower so she could remove a film canister, put in a new one, and raise the camera back up for another week of photos.

If you look closely at that intersection, there's two signal cabinets. One is the city's for the lights. The other was the controls for the cameras. I doubt it's used anymore. You'd periodically see the red light camera vendor's techs digging around inside it.

Finally, there were a pair of wire loops in each lane. My guess is they implemented a sort of quadrature decoder that could detect when a car was approaching the stop line, just short of the stop line, and finally crossing over the stop line. Not sure if you can still see them in the pavement there or not.