Operational Improvements at Traffic Circles: Final Report

Ozbay, Kaan; Bartin, Bekir; Rathi, Neha; List, George; Demers, Alixandra; Wojtowicz, Jeffrey · 2008 · ROSA P / New Jersey. Dept. of Transportation

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Summary

This study addresses the operational inefficiencies and safety concerns associated with legacy traffic circles in New Jersey, specifically the Collingwood, Brooklawn, and Asbury circles. Built in the early 20th century, these facilities were designed for lower traffic volumes and often lack the "yield-at-entry" rules characteristic of modern roundabouts, leading to congestion and accidents. While replacing these circles with modern infrastructure is a viable long-term solution, the high costs and time required for construction motivate the exploration of interim operational improvements. The research aims to evaluate specific geometric and operational alternatives for these three sites using microscopic traffic simulation to determine their impact on mobility and safety. The methodology involved developing and validating detailed simulation models using PARAMICS, a microscopic simulation software selected for its ability to model complex roadway structures and driver behaviors. The models were calibrated using extensive field data, including video surveillance and traffic counts. A critical component of the modeling process was the development of site-specific gap acceptance/rejection models, as the efficiency of these circles is heavily dependent on driver decisions at yield or stop-controlled entries. These models were integrated into the simulation via PARAMICS’ Application Programming Interface (API). Additionally, to ensure realistic interarrival times, the simulations incorporated actual signal timing parameters from traffic signals located in the vicinity of the circles. The study analyzed the current designs alongside proposed operational changes, utilizing factorial design matrices to assess performance during morning and afternoon peak periods. The findings reveal distinct outcomes for each location. For the Collingwood circle, the proposed design aims to convert the facility into a modern roundabout. Simulation results indicated that while this change introduces longer queue times at the approaches due to the new yield requirements, it significantly improves overall efficiency by preventing the circle from locking up, thereby maintaining operational flow. In contrast, the proposed operational changes for the Brooklawn circle were found to increase overall network travel times, particularly during the afternoon peak hours. The Asbury circle served as a baseline case with no proposed operational alternatives, allowing for comparative analysis of current performance metrics. The significance of this research lies in providing a validated framework for evaluating operational upgrades to legacy traffic infrastructure without immediate reconstruction. By demonstrating that specific geometric and operational modifications can mitigate congestion and improve safety, the study offers transportation planners a cost-effective interim strategy. The successful calibration of gap acceptance models within PARAMICS also contributes to the broader field of traffic simulation by enhancing the accuracy of modeling complex, non-standard intersection controls.

Key finding

The proposed design for the Collingwood circle improved overall efficiency by removing lock-ups, whereas the proposed design for the Brooklawn circle increased overall network travel time, especially during afternoon peak hours.

Methodology

simulator

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