| A couple of different ways. The best way is to be inside an unmarked vehicle with the radar or lidar, which is not supposed to alert anybody to the presence of the survey. More frequently (and less accurate IMO), you will see the infamous "counter" black boxes that have a pneumatic tube across the roadway being surveyed. When a vehicle crosses the tube, it activates radar, and a computer records the speed and logs that a vehicle passed. Opens up the possibility that the radar actually recorded the speed of a different vehicle that presented a larger cross section to the radar gun at the time the counter records the vehicle. Usually isn't a major issue due to the law of averages in a 100 vehicle survey (a few wrong readings won't change the 85th percentile).
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01:15:46 11/18/04
