The Optical Barrier is used in the motorway toll lanes to survey the vehicle cadence and to detect the vehicle height above the first axle. These parameters are used to determine the tariff. It consists of two parts (transmitter and receiver), positioned on the sides of a single lane. These parts generate and receive an infrared and orthogonal light in the direction of the vehicle. The two equal elements consist of fibreglass cabinets that include transmitter and receiver cards and the adjustable height detector. This device is exempt from manual regulations and provides a self-diagnostic software that, in case of failure or dirt, allows its operation in a degraded way with a special external signal.