Loop detectors provide accurate and reliable traffic light control. Two inductive loop detectors are cut into each lane, just before and just after the stop line. Every passing vehicle is registered.
A delay time can be set. Any vehicle that passes after that time is photographed twice in quick succession. The first photo shows the offence, the second confirms that the vehicle was actually moving. The camera is set up so that the red light is also visible in the picture.
Loop detection distinguishes between cars and trucks. A separate speed threshold can be installed for each category. The traffic light camera's can also be used to measure speed when the lights are showing green, red or amber.