The California Department of Transportation (Caltrans) freeway sensor network is comprised of: 1) a sensor system of vehicle detector stations (VDS) which measure vehicle occupancy and volume, and, 2) a communication network which transports the data to the Traffic Management Centers (TMCs) in each District. The sensor network is the only source of data used by a District TMC to make freeway operational decisions. Because of its poor reliability, the value of the data from the sensor network is greatly reduced, and this degrades the quality of traffic operations and planning decisions. In an attempt to improve reliability, Caltrans initiated the Detector Fitness Program (DFP). This report presents a study of the reliability of the Caltrans sensor network and the effectiveness of the DFP. The study proposes three sensor network performance metrics: 1) productivity, which measures reliability of the sensor system; 2) stability, which measures reliability of the communication network; and, 3) lifetime and fixing time, which are the number of consecutive days that sensors are continuously working or have failed. The metrics are used to evaluate the differences in system performance in Districts 4, 7, and 11, as well as the effectiveness of the DFP.
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