Evaluating Designs of a Three-Lane Exit Ramp Based on the Entropy Method

Pan, Binghong; Xie, Zhenjiang; Liu, Shangru; Shao, Yang; Cai, Junjie · 2021 · OpenAlex-citations

DOI: 10.1109/access.2021.3070465

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Summary

This study addresses the capacity limitations of freeway diverging areas, which often serve as operational bottlenecks. While expanding two-lane exits to three-lane exits can improve throughput, traditional design methods require excessively long auxiliary lanes, leading to high construction costs and land use inefficiencies, particularly in urban environments. Furthermore, existing Chinese design specifications lack guidelines for three-lane exits. The authors propose and evaluate innovative three-lane exit designs based on a specific interchange in Xi’an, aiming to identify optimal traffic organization methods that balance capacity improvements with geometric constraints. The research employs microscopic traffic simulation using VISSIM software to compare four distinct schemes: the current two-lane exit design (Scheme 1) and three innovative three-lane designs (Schemes 2, 3, and 4). These innovative schemes vary by how an upstream auxiliary lane connects to the ramp lanes (Lane 1, 2, or 3), thereby altering traffic flow organization. The simulation model was calibrated using field-collected data from the Xi’an Gao-Xin Interchange, including vehicle trajectories, speeds, and traffic volumes obtained via radar and drones during peak hours. Key calibration parameters included vehicle composition (4% large vehicles, 96% cars), traffic volumes (4,347 through and 1,594 diverging vehicles), and speed ranges. To objectively evaluate the schemes, the authors applied the entropy method to calculate weights for four performance indicators: traffic volume, delay, CO emissions, and fuel consumption. The results indicate that the innovative three-lane exit designs significantly outperform the traditional two-lane configuration. Specifically, the optimal combination of schemes calculated via the entropy method increased traffic volume capacity by up to 40% and reduced delays by 50–88%. The study demonstrates that by modifying the connection point of the auxiliary lane, designers can achieve substantial operational improvements without the extensive mainline widening required by conventional taper-type designs. This approach effectively alleviates congestion in the diverging area while minimizing infrastructure costs and land usage. The significance of this work lies in providing a practical, data-driven framework for designing three-lane exit ramps in regions with limited space or high construction costs. By validating these designs through calibrated simulation and objective multi-criteria evaluation, the study offers actionable insights for transportation planners and engineers. It suggests that innovative traffic organization strategies can fundamentally improve freeway efficiency and safety, offering a viable alternative to demand-restriction policies or costly infrastructure expansions. The findings support the adoption of these innovative designs in future interchange projects to enhance overall network performance.

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• intersection design