Abstract
The paper presents a microsimulation approach for assessing the safety performance of turbo-roundabouts where Cooperative Autonomous Vehicles “CAVs” have been introduced into the traffic mix alongside 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 such curbs. The paper will then describe the methodological path followed to build VISSIM models of turbo-roundabouts with and without raised curbs in order to calibrate the simulation models and estimate the potential conflicts when a higher percentage 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 the traffic mix of CVs and CAVs. Therefore, it follows that, in absence of crash data including CAVs, the surrogate measures of safety are the only approach in which the safety performance of any roundabout or road entity can be evaluated.
Highlights
Accepted: 2 August 2021The turbo-roundabout concept has been introduced as an alternative roundabout which provides a spiraling traffic flow and requires drivers to preselect the right lane before entering the intersection
Based on vehicle trajectories exported from VISSIM, traffic conflicts were estimated by the Surrogate Safety Assessment Model (SSAM) for single-lane, double-lane and turbo-roundabouts
The literliterature informs us that internal separations improve road safety, since raised lane diature informs us that internal separations improve road safety, since raised lane dividers viders should mark entry, circulating and exit lanes, curbs could be an obstacle in weather should mark entry, circulating and exit lanes, curbs could be an obstacle in weather conconditions, especially when work vehicles must be used for ditions, especially when work vehicles must be used for specific activities
Summary
The turbo-roundabout concept has been introduced as an alternative roundabout which provides a spiraling traffic flow and requires drivers to preselect the right lane before entering the intersection. [14], Giuffrè et al [15] presented a microsimulation-based approach for evaluating the safety performances of roundabouts where different percentages of CAVs were mixed with CVs. Based on vehicle trajectories exported from VISSIM, traffic conflicts were estimated by the SSAM for single-lane, double-lane and turbo-roundabouts. Tollazzi et al [16] showed the benefits of the application of microsimulation to the roundabout evaluation, and the present study confirms that the simulated conflicts could be used to evaluate safety performance of roundabouts in the absence of crash data, including CAVs. Krivda et al [17] highlighted the traffic conflict method based on the sustainable approach. There was better safety performance in the traffic mix of CVs and CAVs
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