Speed is a combined quantity (speed = path/time) with the SI unit m/s. It is derived from length and time. The realization of the unit is carried out by a standard measuring system, a special laser light barrier measuring device.
The following types of measuring instruments for traffic speed are used in Austria:
Radar traffic speed measuring instruments
measure according to the principle of the Doppler effect the speed of vehicles passing the instrument
Laser traffic speed measuring instruments
determine the speed on the base of the change in distance over a certain time. The distances are determined by measuring the time interval between transmission and echo-return of light pulses.
determines the average speed over longer distances (starting from about 300 m) by recording the license plate number at the entrance and the exit of the measuring section and measuring the transit time.
Electronic speedometer (Video traffic control systems)
measure the speed of a vehicle, in which they are built in. While following in constant distance the speed of the followed vehicle is the same.
Distances and speeds of vehicles are determined from a video recording of traffic on a street section measured before exactly.
Sensor controlled traffic speed measuring instruments
measure the time over a distance limited by sensors (pressure sensitive, induction loops, light barriers).
Roller type dynamometers
For two wheeled vehicles: do not measure the speed of driving vehicles, but serve for the determination of a possible maximum speed (type speed) and so for the test of specific requirements for motor bicycles and small motor bikes.