Evaluation of the Accuracy of Stop Bar Video Vehicle Detection at Signalized Intersections

Abstract

Many U.S. agencies have adopted video vehicle detection technology as an alternative to inductive loops. Although many product evaluations have been performed, the majority of these evaluations concentrated on freeway applications in which speed and volume were the primary evaluation criteria. At an actuated intersection, the metrics of speed and volume do not necessarily represent how well a device will operate as a presence detector. Video detection at signalized intersections was evaluated at a test intersection in Indiana. Cameras on all approaches were located at the optimal camera position recommended by the vendors, approximately 60 ft from the strain pole. Two additional cameras were located on each mast arm at slightly less optimal positions, 36 and 48 ft from the strain pole. Traditional inductive loops were also available at the intersection and were used to provide baseline data to screen for discrepancies. Each time the detectors were not in agreement, a discrepancy was noted. A digital video recording was later viewed by a human observer to determine whether the video detector or the loop detector was in error. An analysis of the data showed that video detection was found to produce statistically significantly more false detections and missed detections than the loop detectors on most phases. A small incremental increase in performance was observed when the camera was mounted at 60 ft rather than 36 ft on two of the approaches, but this marginal improvement likely does not justify the additional expense of mast arm, pole, and pole foundation associated with this camera location.