Registered Forum User
 Big Twin
     Posts: 1,956
 Join Date: Mar 2005
 Location: Normally in my own little world
 Mood: I own a flame thrower
  
    
     thought they used the white marks on the road as a second check on speed etc.  I thought they took 2 pic's and measured the change in vehicle position using the lines.  That way then can also calculate your speed, knowing the distance covered in a set time between the 2 pic's being taken.