Classification of busses and lorries in an automatic road toll system

Abstract: An automatic road toll system enables the passing vehicles to change lanes and no stop is needed for payment. Because of different weight of personal cars, busses, lorries (trucks) and other vehicles, they affect the road in different ways. It is of interest to categorize the vehicles into different classes depending of their weight so that the right fee can be set. An automatic road toll system developed by Combitech Traffic Systems AB (now Kapsch TrafficCom AB), Joenkoping, Sweden, classifies the vehicles with help of a so called height image. This is a three dimensional image produced by two photographs of a vehicle. The photographs displays the same view but are mounted with a little spacing. This spacing makes it possible to create a height image. The existing classification uses only length, width and height to divide vehicles into classes. Vehicles of the same dimensions would then belong to the same class independent of their weight. An important example is busses and lorries (trucks) which often have the same dimensions, but trucks often have greater weight and should therefore require a larger fee. This work describes methods for separating busses from lorries with the help of height images. The methods search for variations in the width and height, and other features specific for busses and lorries respectively.