Investigating Implementation Potentials of Turbo Roundabouts in Nevada

Dey, Kakan; Naik, Bhaven; Ashraf, Md. Tanvir; Ndeogo, Bernard Issifu; Hossen, Md Amdad · 2024 · ROSA P / Nevada Department of Transportation

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Summary

This study, sponsored by the Nevada Department of Transportation (NDOT) and conducted by researchers from West Virginia University and Ohio University, investigates the implementation potential of turbo roundabouts in Nevada. The research addresses the operational challenges of traditional multi-lane roundabouts, specifically driver confusion regarding lane choice and safety concerns arising from weaving movements and lane-change conflicts. Turbo roundabouts, which utilize spiral circulatory lanes and raised dividers to restrict lane changes within the intersection, offer a potential solution by reducing conflict points from 24 to 14. The primary objective was to develop guidelines for NDOT by evaluating the safety, operational performance, and driver behavior associated with basic and egg turbo roundabouts compared to traditional single-lane and two-lane designs. The methodology employed a mixed-methods approach comprising microsimulation analysis, driving simulator experiments, and the development of an Intersection Control Evaluation (ICE) tool. Microsimulation models were calibrated and validated to assess throughput, delay, capacity, and surrogate safety indicators (Time-to-Collision and Post Encroachment Time) under varying traffic demands, left-turn percentages, and pedestrian volumes. Concurrently, a driving simulator study involved 24 participants navigating basic turbo, egg turbo, and traditional two-lane roundabouts to measure navigational behaviors, including gap acceptance, speed profiles, and braking. Pre- and post-simulation surveys assessed driver familiarity and acceptance. Key findings from the microsimulation indicated that basic turbo roundabouts achieved a simulated capacity of 3,400 passenger car units per hour (pcu/hr), comparable to traditional two-lane roundabouts (3,300 pcu/hr), while egg turbo roundabouts had a capacity of 2,890 pcu/hr. Safety analysis revealed that basic turbo roundabouts generated 18–30% fewer traffic conflicts than traditional two-lane roundabouts across various traffic compositions. Operational performance was largely unaffected by inner radius variations. Driving simulator results showed distinct behavioral differences: critical gaps were 4.2 seconds for basic turbo, 6.1 seconds for egg turbo, and 3.9 seconds for traditional two-lane roundabouts. Drivers exhibited smoother speed profiles and lower approach speeds on basic turbo roundabouts compared to traditional designs. Survey data indicated that while 88% of participants were unfamiliar with turbo roundabouts, 63% did not oppose their installation post-experiment, and 86% expressed willingness to receive additional education on the design. The study concludes with the development of an ICE tool to assist engineers in selecting appropriate intersection controls based on traffic volume and composition. Recommendations suggest implementing traditional single-lane roundabouts for volumes up to 2,200 pcu/hr, egg turbo roundabouts for volumes under 2,800 pcu/hr, and basic turbo roundabouts for volumes up to 3,400 pcu/hr. The research supports the pilot deployment of turbo roundabouts in Nevada, highlighting their potential to improve safety and capacity while mitigating the weaving conflicts inherent in traditional multi-lane designs.

Key finding

Basic turbo roundabouts demonstrated comparable capacity to traditional two-lane roundabouts while reducing traffic conflicts by 18-30% and eliciting smoother driver speed profiles with lower critical gap acceptance times.

Methodology

mixed_methods

Sample size: 24

Provenance

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

Topics

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• intersection design