Monday, September 11, 2006

Several cities in Oregon (including Portland) and Colorado state police have been reported to use laser radar to catch tailgaters (and speeders). Laser radars can display target speed and range from radar. The police aim the laser radar first at the lead vehicle front bumper, and then at the suspect tailgater front bumper. The officer gets both a range and speed reading on both targets (if targets are close enough to radar to be singled out).

Measuring distance between a moving vehicle and suspected tailgater with a laser radar using radar range information is difficult if not impossible. Laser radar typically takes at least 1/3 second or more to get a speed reading. The radar also displays the last (latest) range measurement (more useful data would be LAST range on lead vehicle and FIRST range on tailgater). Too many parameters are changing too fast to get accurate information about vehicles separation. The lead vehicle length is also a factor (range between rear of lead vehicle and front of tailgater).

To determine vehicle separation accurately the time difference between vehicles crossing a fixed point or landmark should be used (rear of lead vehicle and front of tailgater). If both vehicles are traveling at the same speed (this is usually the case) and a radar can measure the speed -- a timer could be used to calculate vehicle separation. However the timer accuracy required will be on the order of fractions of a second to measure vehicle separation with any accuracy (most difficult).

CopRadar