The following types of speed cameras are used in Avon and Somerset:
Static, spot speed, unmanned cameras in place in the smart motorway sections of the M4 and M5.
The cameras are mounted at the side of the road and use a pair of radar units to monitor the speed of passing vehicles in all lanes of the motorway.
They are linked to video cameras which monitor the Advanced Motorway Indicator (AMI) displays mounted on the overhead gantries. The system can read what speed limit is being displayed and adjust the camera’s trigger threshold accordingly.
When the AMIs are not illuminated or are showing a National Speed Limit sign, the 70mph speed limit is in effect and enforced. There is a one minute grace period following a change of speed limit being displayed, to allow drivers time to adjust their speed safely.
Static, average speed cameras set-up in linked pairs. The cameras use an Automatic Number Plate Recognition (ANPR) system to read the licence plate of every vehicle.
The system knows the exact distance between the two cameras and uses the time it took the vehicle to travel between the cameras to calculate the vehicle’s average speed.
Static, spot speed cameras used for speed or traffic light enforcement.
Mobile, spot speed cameras, operated by a trained member of police staff.
The camera uses pulses of laser light to measure the changing distance between the speed gun and the vehicle being checked.
From this the system can accurately calculate the vehicle’s speed.
All camera equipment used by the Speed Enforcement Unit has been tested and certified as accurate by the Home Office, is calibrated annually (except for SPECS3 cameras like those enforcing the 40mph speed limit at the bottom of the M32 which have approval to be calibrated every two years) and is operated by trained police staff.