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

Sep 29, 2026

Upload by Damian

Access points determine traffic safety along arterial roadways, and the segment between minor road connections and U-turn openings creates distinctive risks due to frequent weaving. A Right Turn Followed by U-Turn (RTUT) design replaces direct left turns with a right turn and downstream U-turn, forcing drivers to rapidly change from slower outer lanes to faster inner lanes. When separation distance is short, limited time and space increase conflicts with through traffic. This study uses UAV trajectory data and a regression framework combining TTC surrogate safety measures across 10 arterial segments to identify how separation distance and operational factors affect conflict risk, providing design guidance for safer arterial facilities.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages23

Reading Time58 min

AccessFree to download

Safety problem and RTUT configuration

Access management and weaving-related conflict risks

Study objective and approach with UAV trajectories and TTC

[www. nature.com/scientificreports](www. nature.com/scientificreports) OPEN Safety evaluation in the weaving segment between minor roads and U-turns on arterial roadways Kimiya Amani, Amin Mirza Boroujerdian􀀍 & MahdiAali Access points play a critical role in traffic safety along arterial roadways. Among the various elements of access management, the segment between minor road connections and U-turn openings presents unique safety challenges due to frequent weaving maneuvers. A widely applied design in such contexts is the Right Turn Followed by U-Turn (RTUT) configuration, an access management strategy that replaces direct left turns with a right turn followed by a downstream U-turn. In these situations, drivers entering from minor roads and intending to make U-turns often need to quickly shift lanes from slower outer lanes to faster inner ones. When the separation distance (SD) between the minor road and the U-turn is short, drivers have limited time and space to accelerate and merge safely, increasing the likelihood of conflicts with through traffic. This study aims to determine the optimal SD and other contributing factors affecting road user safety in RTUT segments. Unlike most previous research that has focused on isolated variables or relied primarily on simulation based analysis, this study integrates multiple geometric and operational factors into a unified regression framework using high resolution UAV trajectory data. By combining field based trajectories with the Time to Collision (TTC) conflict measure, a proactive surrogate safety indicator, the analysis provides a more detailed and reliable assessment of conflict risk compared with traditional crash based approaches. To achieve this, UAV technology was used to monitor 10 arterial segments with SD ranging from about 200 to 500 m (186–488 m). The collected trajectories were compiled into a comprehensive database for regression analysis. Results indicate that SD has the most significant impact on safety, with TTC increasing by up to approximately 1 s for every 100 m increase in SD under maximum entry speeds, highlighting the critical role of SD in mitigating conflicts. Other variables, such as vehicle entry speed, number of lanes, acceleration lane length, and hourly traffic volume also showed statistically significant effects. By integrating UAV based trajectory data with a multivariate regression framework, this study provides a novel and generalizable method for evaluating RTUT safety under real traffic conditions. The findings deliver practical insights for designing safer arterial facilities by optimizing separation distance and other critical geometric and operational factors. Keywords Road safety, RTUT, Time to collision, Weaving segment, Safety performance functions Enhancing safety on arterial roadways is essential, as these routes connect major urban activity centers and playa critical role in the overall performance of the transportation network. Due to the typically high traffic volumeson arterial roads, the probability of severe conflicts increases substantially, thereby elevating the risk of crashes1. Consequently, improving safety along arterial corridors requires a systematic evaluation and implementation of effective strategies aimed at reducing conflicts and enhancing overall traffic safety. One well established approach is access management, which reduces hazardous interactions by regulating and controlling access points along arterial roadways2. Recent research has emphasized that mixed traffic environments, particularly in merging zones, require safety assessments that extend beyond conventional geometric evaluations. For example, He, Xiang, and Wang (2025) examined driver behavior in such contexts and highlighted that unsafe interactions are often the result of limited decision making time and lane changing pressure3. Similar challenges are observed in weaving segments between minor roads and U-turn locations, where abrupt lane tran

FAQs

What safety issue is the study addressing in RTUT segments?

It addresses conflict risk in weaving segments between minor road connections and downstream U-turns, where drivers must quickly merge across lanes while acceleration opportunities are limited.

How does the study measure safety in place of crash-based evaluation?

It integrates high-resolution UAV trajectory data with Time to Collision (TTC) as a proactive surrogate safety indicator, supported by a unified regression framework.

Which factor has the strongest impact on safety results?

Separation distance (SD) shows the most significant effect, with TTC increasing by about 1 second for every 100 meters increase in SD under maximum entry speeds.

Sep 29, 2026

Upload by Damian