The judgement of the traffic condition by using the cluster analysis

The function of an expressway is very important in modern cities, but the increase of traffic demand has created the recurrent traffic jam. The traffic jam is one of the main social problems. As a consequence, drivers desire the provision of accurate information about congestion. This paper proposes a new definition of the degree of congestion based on the analysis of traffic flow. In the present surveillance of congestion, the judgement is composed of two stage procedures. The first procedure is the judgement of congestion at each section, about 1 km. The second procedure is to combine the judgements of sections to the total judgement of a link which is about 5-10 km. The results of the first procedure fluctuate from section to section and therefore the overall degree of congestion of a link which is commonly used in traffic surveillance becomes unstable. This is due to the fact that the judgement of the first procedure is based on only the velocity measured by vehicle detectors. The general theory of traffic flow tells that the traffic condition can´t be accurately judged by velocity. To solve this problem, volume, velocity and occupancy are handled at the same time in analyzing the traffic flow