Improved simulation of driver behavior : modeling protected and permitted left-turn operations at signalized intersections.

Abdel-Rahim, Ahmed; Kyte, Michael; Dixon, Michael · 2011 · ROSA P / United States. Dept. of Transportation. Research and Special Programs Administration

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Summary

This study addresses the need for improved microscopic traffic simulation algorithms, specifically focusing on protected and permitted left-turn operations at signalized intersections. Motivated by the Next Generation Simulation (NGSIM) program’s identification of starting/stopping behavior and permitted left-turn behavior as high-priority areas lacking robust modeling, the research aims to document the microscopic characteristics of these operations. The primary objectives were to identify operational parameters using high-resolution vehicle trajectory data and to describe left-turn phenomena to enhance the accuracy of traffic simulation models. The researchers utilized NGSIM datasets collected from a 2,100-foot segment of Peachtree Street in Atlanta, Georgia, during peak periods in November 2006. The data included high-resolution vehicle positions (accurate to within one foot) recorded every 0.1 second, along with signal timing information. The analysis focused on four key parameters: vehicle turning paths, start-up lost time, saturation flow rate, and speed and time headway profiles. The study examined vehicles in exclusive left-turn lanes, shared through/left-turn lanes, and through-only lanes under both protected and permitted control modes. The findings reveal significant deviations between actual driver behavior and idealized geometric standards. Actual turning paths deviated from the ideal circular path by up to 7.8 feet, with considerable variation among vehicles. In permitted left-turn scenarios, drivers advanced to a distinct "waiting zone" perpendicular to the receiving lane before executing the turn, with the exact stopping point influenced by waiting time and gap availability. Regarding timing parameters, average start-up lost times were 1.79 seconds for through lanes, 1.91 seconds for exclusive left-turn lanes, and 1.86 seconds for shared lanes; these differences were not statistically significant, suggesting the standard Highway Capacity Manual value of 2.0 seconds is conservative. However, saturation headways differed significantly: 2.03 seconds for through lanes, 2.56 seconds for exclusive left-turn lanes, and 2.28 seconds for shared lanes, corresponding to saturation flow rates of 1,773, 1,406, and 1,579 vehicles per hour, respectively. Speed profiles showed that left-turning vehicles consistently traveled slower than through vehicles at equivalent distances from the stop bar, with speed ratios ranging from 0.91 to 0.49. Time headway comparisons showed no clear pattern, though left-turning vehicles exhibited higher headways in the first 50 feet from the stop bar. The significance of this work lies in providing empirical data to refine microscopic traffic simulation models. By documenting the specific deviations in turning paths, the distinct behavior of permitted left-turn waiting zones, and the precise differences in saturation flows and speeds between lane types, the study offers critical inputs for more realistic simulation of arterial operations. These findings challenge the use of idealized geometric paths and conservative default timing values in current simulation software, advocating for models that better reflect actual driver behavior and intersection dynamics.

Key finding

NGSIM left-turn trajectories show systematic deviation from ideal circular paths and a permitted-turn waiting-zone pattern, with lane-use-dependent saturation headways significantly lower for through lanes than exclusive left-turn lanes.

Methodology

dataset

Provenance

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

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• signaling behavior

Information type

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• Empirical Findings: behavioral performance data
• Theoretical Contribution: computational model