Experimental analysis of operational data for roundabouts through advanced image processing

Roundabouts is still the focus of several investigations due to the relevant number of variables affecting their operational performances (i.e., capacity, safety, emissions). To develop reliable models, investigations should be supported by devices and related sensors to extract variables of interest (i.e., flow, speed, gap, lag, follow-up time, vehicle classification and trajectory). Notwithstanding that several sensors and technologies are currently used for data collection, most of them present limitations. The paper presents the investigation carried out to survey vehicle movements at roundabouts as per a comprehensive video image analysis system able to derive the origin/destination (O/D) matrix, compile a vehicle classification, track individual vehicle trajectories together with corresponding speeds and accelerations along paths. To this end, the authors collected video-sequences that were analyzed with a piece of software developed for that task. To minimize the problems due to perspective distortion, environmental effects, and obstructions, a number of camera set-up configurations were adopted with equipment being placed on central or external poles, and on permanent fixtures such as raised working platforms outside the confines of the intersection area. Performance of those installation set-ups with different vehicle tracking strategies has been evaluated. Particularly, speed has been successfully related to trajectory tortuosity, result that emphasizes the tremendous potential of image analysis and opens up to further studies on the evaluation of the operational effects of roundabout geometrics.