Attention is now being directed to noncapital-intensive programs of traffic management which focus on controlling the operation of cars, trucks and buses over an existing highway network so as to achieve a comprehensive set of mobility, safety, energy, environmental and efficiency objectives. This paper deals with the control of traffic flow through improved traffic-signal timing, specifically through real-time, traffic-responsive, traffic-signal systems utilizing digital computers and centralized monitoring stations.The first such system in the Southeast went on line in Atlanta in 1973, with control and surveillance of 21 signalized intersections near Atlanta Stadium. As of mid-1975 the system has been expanded to 50 intersections operating in a responsive mode (plus 178 pretimed controllers in the central business district operating in a time-of-day mode, with manual override for special events). The principal characteristics of the system, including a redundant central processor for stand-by protection against failures, are described.Extensive evaluations of the effectiveness of the traffic-responsive portion of the system have been performed. The impact on speed, stop probability, accidents, vehicle operating cost, motorist time costs, fuel consumption and air pollution has been determined and is summarized.Highly satisfactory evaluations to date have resulted in an Atlanta plan for staged system expansion, described herein, through 1980.