Question:Explain how "average speed" Speed cameras work.
An average speed camera does not measure the cars speed directly.
Instead the system takes a recording of every car license plate passing cameras separated by a known distance. A computer then used "pattern recognition" software to 'read' the license plate. The time for the car to travel the distance between the two cameras is then worked out, by subtracting the time for the first recording of any licence plate from the second time. The speed can then be worked out.
They are called "average speed" cameras because they cannot say how the speed of the car changes along the distance they are monitoring. Many motorists go to fast into the average speed camera zone, stop on the hard shoulder to let their average speed go down.