Safety evaluation in the weaving segment between minor roads and U-turns on arterial roadways

Amani, Kimiya; Boroujerdian, Amin Mirza; Aali, Mahdi · 2025 · DOAJ

DOI: 10.1038/s41598-025-29843-0

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Summary

This study addresses the safety challenges inherent in weaving segments between minor road connections and U-turn openings on arterial roadways, specifically focusing on the Right Turn Followed by U-Turn (RTUT) access management configuration. In RTUT designs, vehicles entering from minor roads must merge into faster inner lanes to execute a downstream U-turn, creating high-conflict weaving maneuvers. The research was motivated by the lack of comprehensive, quantitative design guidelines for RTUT segments, particularly regarding the optimal separation distance (SD) between the minor road and the U-turn. Previous studies often relied on crash data or simulations and examined variables in isolation, leaving a gap in understanding the combined influence of geometric and operational factors on real-world safety. To evaluate these risks, the authors conducted field studies at ten RTUT segments in Mashhad, Iran, with separation distances ranging from 186 to 488 meters. They utilized Unmanned Aerial Vehicle (UAV) technology, specifically a DJI Mavic 2 Pro drone, to capture high-resolution 4K video footage during stable traffic periods. The video data were processed using DataFromSky software to extract precise vehicle trajectories and calculate Time to Collision (TTC) as a surrogate safety measure. A conflict was defined as a TTC value below 5 seconds. After filtering for relevant weaving conflicts, 1,136 events were analyzed. The researchers employed a multivariate linear regression framework, validated by Generalized Additive Models (GAM) and random parameter models, to assess the impact of separation distance, entry vehicle speed, number of lanes, acceleration lane length, and hourly traffic volume on TTC. The results indicate that separation distance is the most significant factor influencing safety in RTUT segments. Specifically, TTC increased by approximately one second for every 100-meter increase in separation distance under maximum entry speeds, demonstrating that greater spacing provides drivers with more time and space to merge safely. Other variables, including vehicle entry speed, the number of lanes, acceleration lane length, and hourly traffic volume, also showed statistically significant effects on conflict risk. The GAM analysis confirmed that the relationships between separation distance, entry speed, and TTC were essentially linear, supporting the use of the linear regression model which explained 71.6% of the deviance. The significance of this study lies in its provision of a novel, data-driven method for evaluating RTUT safety using real-world trajectory data rather than simulations or historical crash records. By integrating UAV-based tracking with surrogate safety measures, the research offers practical, quantitative insights for roadway designers. The findings emphasize the critical role of optimizing separation distance and other geometric parameters to mitigate weaving conflicts, thereby providing a robust basis for improving arterial roadway safety and refining access management policies.

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• intersection design