SURVEY AND ANALYSIS OF VEHICULAR TRAJECTORIES AT ROUNDABOUTS

The paper presents the results of a video survey of vehicular movements at roundabouts which aimed at deriving the Entry-Exit matrix, compiling a vehicle classification, and tracking individual trajectories together with corresponding speeds along paths. To this end the authors utilised a proprietary software called VeTRA (Vehicle Tracking for Roundabout Analysis) which is based on a technique of image analysis. The paper represents part of an extensive research targeted at the validation of operational models for roundabouts. In order to collect video images and minimize the problems related to wind, cloud cover, shadows, and obstructions, several camera configurations were adopted. In fact, five different video camera set-up configurations were considered with equipment being placed on central or external poles, and on fixed locations such as buildings or a raised working platform outside the confines of the intersection area. The five resulting case studies, each with a different video camera set-up, are presented and analysed in the paper. The results obtained suggest that each configuration presents critical aspects that should be addressed separately using appropriate techniques to obtain usable images. On examination of the various options, the best compromise in terms of video quality and elaboration costs would appear to be the one using an external pole. Furthermore, from an analysis of video records the authors derived a relationship between operating speed and trajectory that demonstrates the benefits resulting from the imposition of deflected trajectories on drivers by geometrical elements designed to curb driver speed in the circulatory roadway, and approaching and departing arms.