AbstractThis paper discusses the traffic flow measurement system (TMS) based on the idea of vehicle cluster. TMS is an experimental system which aims at the accurate real‐time measurement of the traffic flow parameters (location of vehicle, speed, congestion, location of the queue tail, etc.) which is spread in space, using the image processing technique. As image processing techniques, the line‐differentiation and the clustering based on the idea of vehicle cluster are used. By this scheme, traffic flow phenomena in the region of measurement can be measured directly. By introducing the idea of vehicle cluster, the measurement can adaptively be performed, observing the individual vehicle in low traffic and a set of vehicles in heavy traffic. As a result of the traffic flow measurement experiment using the proposed system, the following observations are made: (1) the measurement can be performed throughout the day; (2) the real‐time measurement with 200‐ms intervals can be performed; (3) the recognition rate for vehicle cluster is 97 percent or more for the range of measurement 150 m. The accuracy of vehicle speed measurement is ±13 percent (for the range of measurement 40 m); (5) the accuracy of vehicle height measurement is within ±10 percent (for the range of measurement 100 m an when the observation of individual vehicles is possible); and (6) the tail of the queue can be i