speed cameras?

Question

Yesterday I was traveling on a long stretch of road with a couple of speed white painted lines on the road every so often. I was just crusing at about 100mph and forgot about my speed and suddenly noticed a police van parked up in the distance right along a set of speed white lines. When I suddenly slowed down, question is the road is a long straight, does anyone know do they get you right from a set distance like when I would of been doing 100mph or just when you go over the lines that they are parked up next to? Cheers

I'm also from the U.K

Answer 1

the lines on the road are used for police airplanes to track your speed and radio ahead to a waiting police officer.this is known as a speed trap. i once got a ticket and told the officer that my radar and laser detector never went off how did he know i was speeding?he said by aerial view and pointed to a plane flying over the highway. unfortunatley i have been caught 2 x this way !!!!