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Traffic signals were first introduced for reasons of safety by providing the right of way to the intersecting traffic in a fixed sequence. It was soon found, however, that a signalized intersection could be used more efficiently by properly timing the traffic light in accordance with the amount of incoming traffic. Further improvement in efficiency was then achieved by coordinating the timing of the traffic signals along a traffic artery. With the advent of computer technology, coordination of signal timing is now extended to cover the two-dimensionally distributed traffic signals in such a way that the timing adaptively follows to the changes of the traffic pattern in the area. Information from a large number of traffic detectors are now automatically collected, processed, and fed to the centrally located wall-map displays as well as to the remote roadside displays to provide the traffic officers and the drivers with such information as congestion, accident, frozen surface, etc. This paper outlines the problems, methods, and principles of the road-traffic control and describes the state of the art with reference to the Tokyo Traffic Control and Surveillance System. Some of the results of floating car surveys, the accident statistics as well as the estimated reduction in exhaust emission and fuel consumption are also presented.