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Systems have been installed in several cities in the United States, including Los Angeles, Calif., which allow real-time surveillance and control of freeway traffic. The surveillance function is effected by a system of presence detectors located on the freeways, telemetry, and digital computer processing. Traffic control is effected by using traffic signals to meter traffic entering the freeway through on-ramps. Current research on modeling freeway traffic flow, estimation of traffic conditions from presence-detector data, and control of freeway traffic is utilized to provide a design of a surveillance and control system for a segment of the Hollywood Freeway in Los Angeles. In some aspects of the design, particularly the design of traffic-responsive on-ramp metering algorithms, a sound theoretical foundation which adequately accounts for practical constraints has been established. In other areas, preliminary ideas are presented and approaches to optimal schemes outlined.