A recent ruling by the Supreme Court may have significant impact on traffic cameras. The SCOTUS ruling said that defendants have the right to challenge their accusers in court, and that the prosecution couldn't simply produce a certificate saying someone (e.g., a lab technician) had produced incriminating evidence.
This strongly suggests that traffic camera violations can be challenged by demanding that those who test and certify these machines show up in court under oath. In many cases the camera companies are compensated based on the volume of violations reported--and are also responsible for the calibration and maintenance of the machines. This ruling could put this conflict of interest right into the courtroom.