Models for Quantitative Assessment of Video Detection System Impacts on Signalized Intersection Operations

Various models are presented for quantitative assessment of the impacts of video detection system applications at signalized intersections. The models are developed mainly to address the occlusion issue, one of the unavoidable phenomena associated with video detection systems. Two types of occlusion scenarios and their potential impacts on intersection operations are analyzed on the basis of typical parameter values and detection setup. Also addressed are the limitations of video detection systems in providing advance detection. Occlusion in video detection systems can result in missing detections, false detections, and increased detector presence time and thus may affect intersection operations under actuated control. It is found that missing detections due to occlusion to the following vehicles are generally less than 5% when the approach volume is less than 600 vphpl and the proportion of trucks is less than 5%. At this traffic volume level, additional phase extension time caused by occlusion is generally less than 3 s. To minimize false detections due to occlusion to adjacent lanes, the horizontal offset between the camera and the travel lane should be at the minimum, with an ideal mast-arm mounting and positioning to the division line between the lanes. Because of limitations on the achievable camera height and mounting angle, it is found to be difficult to use one camera to satisfy the required advance detection for speeds over 50 mph. The study does not address the impacts of physical limits of video detection systems such as pixel size, grayscale depth, lighting, and shadows.