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USE OF DETECTOR OCCUPANCY FOR REAL-TIME ASSESSMENT OF SIGNAL CONTROL

Current signal control systems generally lack the ability to perform real-time assessment of their own control efficiencies. This deficiency not only creates difficulties in systems management but also hinders the development of intelligent signal control systems. Because of these implications, automatic real-time assessment of signal control has been identified by the Transportation Research Board Committee on Signal Systems as one of the most urgent research problems. Conventional inductive loop detectors and emerging video image processing systems are among the vehicle detection systems that may be deployed to make real-time assessment of signal operations possible. Most existing signal control systems rely on small-area inductive loop detectors to monitor traffic conditions. Typical dimensions of such detectors are 6 ft x 6 ft (1.8 m x 1.8 m). When a video image processing system is used, numerous virtual detectors can be placed within the view of a camera to simulate inductive loop detectors. Data collected by inductive or virtual loop detectors may be used to estimate occupancy, flow rate, average speed, and other traffic parameters. Occupancy refers to the percent of a sampling period in which a detection area is occupied by vehicles. This parameter is an indicator of the degree of congestion, and it is potentially a useful parameter for real-time assessmenet of signal control strategies. Occupancy has been used for years to monitor the operations of freeway systems, but very little is known about the characteristics of occupancy on urban streets. To guide the development of a system for real-time assessment of signal control, this paper examines the following aspects of occupancy: the impact of detector placement on the usefulness of occupancy data; the ability of occupancy to reveal the real performance of signal control; and the potential use of occupancy and related detector data for real-time assessment of signal control.