Counter counter pneumatic tire was the first unit to measure traffic. It is commonly used for temporary measures. vehicle is detected when it passes over the rubber tube attached to the floor. The passage of the vehicle wheels compresses the air in the tube. Pressure variation induced is detected. This sensor has the disadvantage of not counting vehicles but axles. Intensitées are expressed in the number of vehicle units, intensities obtained by dividing the number of axles recorded by two. Counters tires new generation (2 tubes) distinguish different types of vehicles and allow the measurement of speed. Through these counters, the knowledge of HGV traffic is becoming widespread. The principle is to place two parallel tubes at a distance well known. Knowledge of the distance and the time of passage of the first tube to give the 2nd speed of the first axle of a vehicle. The speed of the first axle of the vehicle is known, the distances of the other axle relative thereto can be determined as well as the outline of the vehicle.
