I was always under the impression that the lines are there to determine what speed you were traveling. If you pass the camera speeding it will flash once as you enter onto the lines and again as you near the end of the line. They then see how many lines you have passed in a certain time frame to work out the speed you were traveling. If it a forward facing camera it's different, can't really have a giant flash when you are driving towards it.
Beat me to it. Not the fastest typing on my phone!!
Forward facing cameras, the Truvelo type have a magenta filter on the flash - they do flash. They have 3 lines on the road infront of the camera, and and 2 induction loops set into the road before them. As you pass over the loop it activates - and measure the speed between the 2 loops - if you're speeding it takes a picture, and the 3 lines indicate how fast you were going.
- Edit - the megenta lines is because as you may be aware red light does not dazzle or ruin your night vision - hence internal lights on ships is red at night time. And is used in photographic dark rooms..
As someone else said the lines on a Gatso indicate 5mph each - the radar says you're speeding and it takes 2 pictures - the number of lines between each picture are counted and you are sent a ticket based on that.
Average speed cameras use numberplate recognition between two points
there is also a third type, which has the 2 induction loops in the ground and a grey post which has a socket in it, where a speed camera van can plug itself in. This is a part time speed trap - and is used for mobile speed monitoring from a distance. I don't know how they work legally now cause usually the plugged in van is around the corner from the loops..hence it's location..
Edited by -AJ, 14 June 2012 - 03:28 PM.