Safety evaluation of turbo roundabout with and without internal traffic separations considering autonomous vehicles operation

The paper presents a microsimulation approach for assessing the safety performance of turbo-roundabouts where Cooperative Autonomous Vehicles “CAVs” have been mixed with conventional vehicles “CVs”. Based on the analysis of vehicle trajectories from VISSIM and subsequent analysis of traffic conflicts through the Surrogate Safety Assessment Model (SSAM), the research aims to evaluate the safety benefits of turbo-roundabouts where the lanes are physically separated by raised curbs compared to roundabouts without curbs. The paper shall also lead to describe the methodological path followed to build VISSIM models of turboroundabout with and without raised curbs, to calibrate the simulation models, and to estimate the potential conflicts when the percentages of CAVs are introduced into the traffic mix. A criterion has been also proposed for setting properly the principal SSAM filters. The results confirmed both higher safety levels for turbo roundabouts equipped with raised lane dividers compared to turbo roundabout solutions without curbs, and better safety conditions under traffic mix with CAVs. Therefore, it follows that in absence of crash data including CAVs, the surrogate measures of safety are the only approach to evaluate the safety performance of a roundabout and any road entity