We had one here for a couple of years. The cameras and radar start taking a series of photos and speed readings slightly before the light turns red. An officer reviewed the photos and speed readings to determine if a ticket was sent. If you maintained the same speed or slowed as you went through the intersection you were very likely to not get a ticket if it were close. If you accelerated through the intersection, they figured you were trying to beat the light.
They also considered that if you were behind a large truck and couldn't see the light until you were in the intersection. As long as it was a slow speed situation, they didn't send a ticket.
The 1st year lots of tickets were issued. But the state legislature passed a law requiring the yellow light had to stay on for 1 full second longer at lights with cameras than other intersections. That 1 extra second meant that the number of tickets issued the 2nd year was way down. It was costing the city more to have the cameras than they were bringing in from fines. After the 2nd year they took them down and kept the extra 1 second on the yellow light.
