We've got a couple of these cameras along one of the routes that I take to and from work. Here's how it works. During very light traffic (such as at 0500 AM, when I drive to or from work), the automated traffic system is designed to keep a green light along the main thoroughfares unless someone pulls up on a side road and triggers the light. Absent any side road traffic, the light defaults to green for the main road. This maintains a smooth, unencumbered flow of traffic.
This works fine for every traffic light except two - can you guess which two? Yep, the ones with the red light cameras. They not only turn red for no apparent reason, but they do so frequently. I've timed the green on one of them, and it's 15 seconds long.
As you said, the purpose of most of these cameras is to gain revenue, not enhance safety.
BTW, I'm old enough to remember the 3-second rule at red lights. What is the "3-second rule", you ask? When driving in bad neighborhoods in Cleveland, Ohio, the unwritten rule was that when you came upon a red light, you'd stop for 3 seconds, look both ways, and proceed through the light. Back in those days, you were not very likely to get a ticket for doing so as long as you did it safely. It wasn't wise to loiter at a traffic light in a bad 'hood at 3 AM.
In Dallas they were caught decreasing the length of the yellow light. This gives drivers less time to react resulting in more revenue for the private company.
Here in Florida they just passed a state law allowing these. Despite that several cities had already installed them and were handing out tickets they were legally prohibited from issuing.
Whats so hard about putting a cop at a light to hand out tickets? Seems people would learn their lesson and stop running red lights.