Vehicle counting is becoming a common requirement for car parks regardless of their size. It is a great convenience for visitors to be aware of the number of available spaces before they enter a car park or venture into another section of the car park. Traffic monitoring on roads is also becoming commonplace as highway authorities and council transport departments strive to reduce congestion.

For vehicles to be automatically counted, there needs to be a means of detecting them. The most common form of vehicle detection uses an inductive loop buried in the road surface. As a vehicle passes over the loop, the loop inductance changes causing the loop monitoring circuit (loop detector) to output a signal. If two such loops are placed close together along the path of the vehicle, the direction in which the vehicle is travelling can also be detected. In car park applications, loops need to be placed in each entrance and exit lane as well as on the ramps between levels. The counting system receives the signals from the loop detectors and maintains a count of vehicles entering and exiting each area. It then computes the data as necessary to provide the required display information and/or alarm signals.

Typically, the counting system will provide comprehensive on-screen information to the management and/or display count values at key locations around the car park using Variable Message Signs (VMS). The counting system may also have 'count thresholds' set so that it can raise an alarm whenever a count reaches a critical value.