Speed Cameras

[BertiWooster]

Following on from the question below about SPECS speed cameras

How does 'ordinary' speed cameras work - the ones where there is a camera followed by white lines going across the road

[MarkRae]

It takes two photographs a defined interval apart and then compares how far the photographed car has travelled during that interval using the lines on the road. This gives the car's speed.

[BertiWooster]

What triggers the camera to take the photos , in the first instance ?

[anacryp]

The camera has a speed detector and will only flash if the vehicle is travelling over the speed limit.