Warning systems are being developed for left-turning vehicles at intersections where protected left-turns are not warranted or cannot be provided, based on limitations of right of way or intersection capacity. These are meant to provide warnings to left-turning vehicles of vehicles approaching from the opposite direction, when the time to turn may be deemed unsafe. To implement these warning systems, it is necessary to estimate in near real time, the probability of conflict between the two approaching vehicles. A study is being conducted with the help of video and radar at various intersections, to obtain estimates of turning time and acceptable gaps for drivers under various situations. Initial pilot observations indicate that the presence of pedestrians in intersections had an immediate and substantial impact on movement of left turning vehicles. From a preliminary systematic video analysis of the intersection, in the presence of pedestrians on the destination crosswalk, the mean and standard deviation of both the gap and gap components (i.e., turning time and the “buffer” between the turning vehicle and the next oncoming vehicle) increased. On the basis of these observations, pedestrian-detection mechanisms may be useful in such intersection warning systems, with a threshold for warning that is adjusted for pedestrians when they are present or in the vicinity of the destination crosswalk.
November 15, 2004