The answer is simple, less cameras and more cars on patrol. A fixed camera only slows traffic for about 100 yards, usually with a plethora of brake lights followed by rapid acceleration.
No, a partol car, a human being (I think!!) that can apply a bit of discretion, judge the road conditions and judge whether 35 is too fast, just moving with the flow of traffic or a brief excursion to overtake safely.
Besides, when the bank down the road was robbed, the gatso outside was unable to give chase and as the robbers didn't run faster than 30mph, the useless thing didn't even take a picture!