Or, more importantly, what are red light cameras supposed to do?
This recent post by the National Motorists Association points to a number of studies that claim that red light cameras increase accidents. I haven't read much about red light cameras, and I am ambivalent about them in general, but I don't think that accidents are the main cause rationale for their installation. I know in some cases accidents are the main concern, but from the perspective of Los Angeles traffic, the main benefit is in traffic flow. Red light cameras deter cars from cruising through the intersection at yellow as well as they probably have some type of positive effect on gridlock conditions.
There is no doubt that red light cameras are not a panacea for many traffic problems. They have been declared unconstitutional (at the state level) in Minnesota on two levels. First, the city cannot enforce traffic laws that are not consistent with the rest of the state (I think this ruling deserves further thought about it's implications). Second, the court ruled that the law violated the presumption of innocence because the driver may not be clearly identified. Whether this case affects the remainder of the country in unclear.
Perhaps the takeaway point from all of this is that greater consideration should be given to employing traffic cops at busy intersections. Having people direct traffic works very well and limits scofflaws and accidents. How to pay for the traffic cops is another story, but if the goal is to improve traffic flow they should be considered. If the goal is simply to raise revenue, as the NMA argues, then rather than red light cameras each city should charge a toll on the roads on at their borders.