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How Police Measure Your Speed

Posted Thursday, August 2, 2018 by Andrew Charles Huff

*Laser Speeding Tickets*Laser devices, also known as LIDAR (light distance and ranging), measure a car’s speed by using a time/distance calculation. A narrow band of light originates from the laser device and is aimed at the target vehicle and the time it takes the reflected light to return to the laser device is measured. Because the speed of both the original light pulse and its reflection are traveling at the same speed (the speed of light), differences in the time it takes the transmitted light to strike the target vehicle and return can be used to calculate the speed of the vehicle and serve as the basis for a laser speeding ticket. Unlike radar, lasers can pinpoint specific vehicles in heavy traffic.

*Radar Speeding Tickets*Radar guns aim an electromagnetic signal at a target vehicle and pick up the return signal reflected off the vehicle. The doppler effect causes the frequency of the return signal to shift by an amount dependent on the relative speeds of the source of the original signal and the target. Speed radar devices measure the frequency of the reflected signal and compare it with the frequency of the original signal to determine the speed of the target vehicle. A radar beam varies in width comparative to its length-the further the radar’s “zone” extends from the unit the wider it will be. An officer who issues a radar speeding ticket should be certain that the radar was not inadvertently picking up any other moving objects that may also have been within the radar’s “zone”.

**Speeding Tickets by Pace

**Also known as a “pace”, the clock and follow method is where an officer moves his vehicle behind another, keeps a uniform distance between the two vehicles for a certain distance and then uses the reading on his speedometer to measure how fast the target vehicle is driving.

*Speeding Tickets by Aerial Speed Measurement*Police officers in aircraft measure vehicle speeds by monitoring the time it takes the target vehicle to travel between two or more marked spots on the road which are spaced a known distance apart. Information is transmitted to officers on the ground who then issue speeding summonses.