Accelerating Roundabout Implementation in the United States - Volume V of VII: Evaluation of Geometric Parameters that Affect Truck Maneuvering and Stability

Rodegerdts, Lee A.; Griffin, Ashleigh; Steyn, Hermanus; Ahmadian, Mehdi; Hou, Yunbo; Taheri, Mehdi · 2015 · ROSA P / United States. Department of Transportation. Federal Highway Administration. Office of Safety

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Summary

This report, Volume V of the Federal Highway Administration’s "Accelerating Roundabout Implementation in the United States" series, addresses the critical issue of truck stability and rollover risk at roundabouts. While existing design guidance adequately covers horizontal alignment and swept paths for large trucks, there was a lack of comprehensive research in the United States regarding how the combination of horizontal alignment, vertical alignment, cross-section, and curb treatments affects truckload instability. The study aims to provide practitioners with data-driven insights to enhance safety and accommodate freight movement effectively. The research methodology combined a literature review, an analysis of a sample of truck overturn incidents at roundabouts, and extensive multibody dynamics simulations. The simulation model evaluated the impact of various design and behavioral factors on truck stability in both single-lane and two-lane roundabouts. The study tested three truck configurations: a baseline WB-67 semi-truck, a single-unit truck, and a B-train tractor with double trailers. These were modeled under three load conditions (full, half-full, and empty) to assess lateral stability. Key roadway variables included the inscribed circle diameter (ICD), circulatory roadway cross-sections (varying cross-slopes and the presence of truck aprons), and overall roundabout tilt. Entry and circulating speeds were also varied to determine their influence on lateral acceleration. The simulation results identified truck speed as the most significant factor affecting stability, followed by the cross-sectional geometry of two-lane circulatory roadways and the use of truck aprons. The study utilized a Rollover Index to quantify stability risks across right turns, through movements, and left turns. Findings indicated that larger roundabout diameters generally reduced the peak rollover index. In two-lane roundabouts, the presence of a truck apron and specific road crown configurations significantly influenced stability, particularly during left turns and through movements. The analysis also revealed that truck configuration and load weight impacted stability, with heavier loads and specific trailer configurations showing varying degrees of susceptibility to rollover depending on the maneuver and speed. The significance of this work lies in its contribution to safer roundabout design for freight transportation. The report concludes with design considerations emphasizing the importance of appropriate circulatory roadway cross-sections, the strategic use of truck aprons, and speed management. It also highlights the need for education programs and driver practice to mitigate risks. By identifying the specific geometric parameters that most affect truck stability, the study provides actionable recommendations for engineers to design roundabouts that safely accommodate large trucks, thereby supporting the broader goal of accelerating roundabout implementation while maintaining high safety standards for all road users.

Key finding

Truck speed was the most significant factor affecting stability, followed by the cross-sectional geometry of two-lane circulatory roadways and the use of the truck apron.

Methodology

modeling

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

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• intersection design