Fixed safety cameras
These are located where three or more people have been killed or seriously injured over a 1.5km stretch of road, in the three years prior to installation.
The cameras, in yellow housings, use radar to detect the speed of passing vehicles. The camera is activated when a vehicle crosses a radar beam at excessive speed. It takes two photographs, on 35mm colour film, of the rear of the vehicle at an interval of 0.5 seconds. A series of short white lines are painted on the surface of the road, five feet apart, as an independent way of veryfying the speed reading on the film.
Because two photographs are taken of the speeding vehicle, it is possible to compare these and work out how far the vehicle has travelled in the interval using the check marks on the road. Using a simple formula, the viewer of the film can verify the speed given by the camera. The secondary check marks are there to safeguard the motorist against a faulty or false camera reading.
Truvelo and Traffiphot
These cameras, also in yellow housings, use sensors embedded in the road to measure the speed of oncoming vehicles and photograph the front of vehicles using 35mm colour film. They are also able to photograph the rear of vehicles.
The system works out how fast the vehicle is travelling, according to the information received from the sensors in the ground. The vehicle speed is calculated the moment the front axle crosses the last sensor but a photograph is only taken when the camera expects the vehicle to reach three marker lines; 1.8 metres beyond this point. The time taken to travel the 1.8 metres is recorded in milliseconds on the negative alongside the speed. An operator also checks the photograph manually to ensure the vehicle has reached the marker lines as expected by the camera.
Mobile safety camera vans are also used to supplement our fixed safety camera sites.