Safety Evaluation of Turbo-Roundabouts with and without Internal Traffic Separations Considering Autonomous Vehicles Operation

Giuffrè, Tullio; Granà, Anna; Trubia, Salvatore · 2021 · Crossref

DOI: 10.3390/su13168810

archive: archived pipeline: cataloged verified

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Summary

This study addresses the safety evaluation of turbo-roundabouts, specifically comparing configurations with raised internal lane dividers (curbs) against those relying solely on road markings. The research is motivated by the global variation in turbo-roundabout designs—often influenced by operational constraints like snow-plowing—and the emerging need to assess how these infrastructures perform when Cooperative Autonomous Vehicles (CAVs) are introduced into traffic mixes alongside Conventional Vehicles (CVs). Since crash data involving CAVs is currently unavailable, the authors utilize surrogate safety measures to evaluate potential conflicts and safety performance. The methodology employs a microsimulation approach using the VISSIM software. The researchers developed models for turbo-roundabouts with and without raised curbs, calibrating the simulations against field data collected from 14 intersections. Calibration involved adjusting parameters such as standstill distance, look-ahead/look-back distances, and temporary lack of attention to ensure the simulated driving patterns matched observed behaviors, verified using the GEH index. Traffic flow scenarios were derived from field observations, with heavy vehicle percentages capped at 5%. To assess safety, vehicle trajectories exported from VISSIM were analyzed using the Surrogate Safety Assessment Model (SSAM). The study also proposes a specific criterion for setting SSAM filters to accurately account for the presence of CAVs in the traffic mix. The results indicate that turbo-roundabouts equipped with raised lane dividers exhibit higher safety levels compared to those without curbs. Furthermore, the introduction of CAVs into the traffic mix resulted in improved safety conditions for both roundabout configurations. The analysis confirmed that surrogate measures of safety, derived from simulated traffic conflicts, are effective tools for evaluating the safety performance of road entities in the absence of historical crash data, particularly for emerging vehicle technologies. The significance of this work lies in its validation of microsimulation and surrogate safety assessment as viable methods for evaluating infrastructure safety under mixed-autonomy traffic conditions. By demonstrating that raised curbs enhance safety and that CAVs contribute to safer traffic operations, the study provides evidence-based insights for urban planning and infrastructure design. It highlights the importance of physical traffic separations in turbo-roundabouts and supports the use of simulation-based conflict analysis as a standard approach for assessing safety in the era of autonomous driving, where traditional crash statistics are insufficient.

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• intersection design