The study is here: Caution---Red-Light-Cameras-Ahead
Very interesting discussion of the hazards of "fee-for-service" contracts, plus an attempted rebuttal from the private-firm trade association, who naturally like these contracts.
Summary from the article:
A new study found that contracts between the companies responsible for red-light and speed cameras and municipalities can include payment incentives that put profit above traffic safety. Some of the contracts also limit the ability of governments to set and enforce traffic regulations, the U.S. Public Interest Research Group (PIRG) said. The report . . . said that red-light violation mitigation techniques such as lengthening the duration of yellow lights potentially could lead to financial penalties in some jurisdictions...The findings also revealed that some contracts include language that could also penalize municipalities if they don’t approve enough traffic tickets that come from camera systems. For example, the report notes that in Walnut, Calif., the city has a contract with the vendor Redflex that has a possibility of a financial penalty if the city waives more than 10 percent of violations from the cameras.