Vehicle Level Evaluation of Loop Detectors and the Remote Traffic Microwave Sensor

Abstract

Traffic detectors support most traffic management applications, so it is important that a detector performs as expected. This study evaluates the performance of four loop sensor models and the remote traffic microwave sensor (RTMS), adding to the body of sensor performance knowledge through the use of new analytical techniques. The study collected contact closure data from all five of the detectors and concurrent video data. Each loop sensor was deployed following Caltrans guidelines for at least 24 h across dual loop detectors in each lane of I-80, north of Oakland, Calif. The research examined various distributions of the individual vehicle actuations from each of the detectors. This exercise found some of the loop sensors locked up and did not provide any data to the controller although they appeared fully functional from the front panel. The sensitivity appears to vary between the RTMS and the loop sensors, as well as from one loop sensor model to the next, which means the occupancy measurements will also change. Detailed analysis of the sensors used the video to manually validate each vehicle passage over extended periods, preselected at random, with the errors classified by type (e.g., nondetected vehicle) and source (e.g., due to a lane change maneuver). As presented herein, the RTMS exhibited problems due to occlusion and reflections, while two of the loop sensors exhibited non-negligible problems. Finally, the methodology used in this paper can easily be extended to validate other detectors and detection technologies.