Lidar speed gun

Lidar has a wide a range of applications; one use is in traffic enforcement and in particular speed limit enforcement, gradually replacing radar after 2000. Current devices are designed to automate the entire process of speed detection, vehicle identification, driver identification and evidentiary documentation.

Lidar is a portmanteau of 'light' and 'radar', and an acronym for 'light detection and ranging' or 'light (laser) imaging, detection and ranging'. Unlike 'radar' ('radio detection and ranging') which is now regarded as a word, not an acronym, there is no consensus on capitalisation, however 'lidar' is in use, for example by The New York Times. A use of the acronym occurred in 1953 and of the portmanteau in 1962.

Lidar was used in the 1930s, further development occurred after the invention of the laser in 1960, from 1964 NASA has used lidar to map the earth and planets. Jeremy Dunn (Laser Technology Inc.) developed a police lidar device in 1989, and in 2004 10% of U.S. sales of traffic enforcement devices were lidar rising to 30% in 2006, given the advantages of lidar it appears likely that the majority of current sales are lidar, although sophisticated radar units are still being sold.

Current units combine five operations; speed detection; operator viewing, even under adverse conditions; imaging synchronised with speed detection; acquisition of court ready evidence; downloading of evidence to an external device. They can operate in automatic mode either attended or unattended.

Radar has wide signal beam divergence, so that an individual vehicle cannot be targeted, requiring significant operator skill, training and certification in order to visually estimate speed so as to locate an offender in a traffic stream, and offenders may use the defence that some other vehicle was offending. Radar will register the speed of any object in its field, for example a tree swaying or an airplane passing overhead.

Lidar has a narrow beam, and easily targets an individual vehicle, thereby eliminating the need for visual estimation, and records an image of the license plate at the same instant as recording the speed violation. Speed estimation takes less than half a second which together with the narrow, targeted beam results in offending vehicles having little warning even when using an evasion device. Lidar can measure the distance between vehicles to detect 'too close' (tailgating) infringements. The speed of a vehicle in the shadow of another vehicle cannot be measured.

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Wikipedia