Lateral and Tangential Accelerations of Left Turning Vehicles from Naturalistic Observations 2019-01-0421

Intersection collisions involving left-turning vehicles represent a significant portion of collisions, and accident reconstructionists are often tasked with determining the relative timing and spacing between two vehicles involved in such a collision. This time-space analysis frequently involves determining or prescribing a path and acceleration profile for the left-turning vehicle. Although numerous studies have examined the typical straight-line acceleration of vehicles, few have studied the tangential and lateral acceleration of left-turning vehicles. The authors made observations at three intersections. Each intersection incorporated permissive green turn phases for left-turning vehicles. The authors recorded video of left-turning vehicles at each intersection from an unmanned aerial vehicle, and that video was analyzed with a convolutional neural network designed to detect vehicles. The detected vehicles were then tracked over time and the results were compiled and analyzed. A total of 129 left-turning vehicles were analyzed. In some of the observed turns, an oncoming vehicle was also visible in the video. The spatial relationship between the oncoming vehicles and the left-turning vehicles was analyzed and the relationship between gap acceptance and tangential acceleration is presented.