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In order to stop people from driving above the speed limit and by doing so reducing the likelihood of accidents, traffic police use different systems for speed detection: radar devices, loop technology, light beams, video systems (fixed and mobile), LIDAR and a combination of the above.

 


The laser beam is very narrow as opposed to a radar beam (on 500 m around 2,5 m in diameter), that is why LIDAR can be used in heavy traffic. The measuring starts from the moment the trigger is pressed on the LIDAR. In the next 0.5 s the LIDAR takes 50 measurements and calculates the speed of the target using these measurements. Since it uses light the range depends on weather conditions and the target area. The range of the LIDAR is reduced when dealing with a smaller target area and less light reflection. The area of a vehicle with the greatest reflection is the licence plate. If the vehicle has no licence plate the range of the LIDAR is halved.

The most popular LIDARs in Europe are: LTI Marksman 20.20, LTI Ultralyte, Prolaser III and the Jenoptik LaserPatrol (TraffiPatrol). Their characteristics are similar. The maximum range of LIDAR in ideal conditions is around 800 m, while in average conditions this is reduced to 350 m.

Traffic Radars. The traffic radar works by continually sending and monitoring returning radio waves. When a radio wave hits a moving object its frequency changes. The precise change in frequency depends on the speed of the object and the direction of travel. This is known as the Doppler Effect.

 

Mobile video system (Vascar, Travimo). The Travimo video camera is installed in a police vehicle that follows a vehicle whose speed it is trying to determine. The minimal travel distance required to determine vehicle speed is 200 m - during which the speed of the following vehicle should be kept steady in order to gauge correctly the speed of the followed vehicle.

 
LIDAR, Light Detection And Ranging. The LIDAR unit emits a narrow laser beam towards the target, the beam is then reflected and a small part returns to the unit. The time that passes from the emission to the reception of the laser beam is measured in the LIDAR unit which then determines the distance to the target.

 
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