Conventional Diamond, Diverging Diamond, and Single Point Diamond Interchanges: A Comparative Operational Performance Evaluation in the Era of Connected Vehicles

Alzoubaidi, Mutasem; Zlatkovic, Milan · 2022 · Crossref

DOI: 10.31075/pis.68.03.01

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Summary

This study evaluates the operational performance of three interchange designs—Conventional Diamond (CDI), Diverging Diamond (DDI), and Single Point Diamond (SPDI)—in the context of Connected Vehicle (CV) technology. Motivated by the need to mitigate traffic congestion and the lack of research on the combined effects of unconventional interchange geometries and CVs, the authors aim to determine how interchange design and CV market penetration rates (MPRs) influence traffic mobility. The research employs a microsimulation approach using VISSIM software, integrated with ASC/3 Software-in-the-Loop signal controllers and Python-programmed Vehicle-to-Infrastructure (V2I) communication algorithms. The study area is the intersection of I-15 and 12300 S in Salt Lake County, Utah, currently configured as an SPDI. The authors created nine simulation models representing each of the three interchange designs at three CV MPR levels: 0%, 50%, and 100%. CV behavior was modeled using a modified Wiedemann-74 car-following model, activated when vehicles entered a 1,000-foot communication radius. The base model was calibrated and validated using field data from the Utah Department of Transportation, achieving a GEH statistic of 0.22 and an R² value of 0.97 for phase green times, ensuring high fidelity. Performance metrics included mean vehicular travel times, delays, queue lengths, and the number of stops, averaged over 10 randomly seeded runs. The results indicate that interchange design has a significantly greater impact on traffic operations than CV market penetration. Specifically, increasing CV MPR from 0% to 100% reduced delays by only 6.4% across all designs. In contrast, geometric configuration caused substantial variations: converting an SPDI to a CDI increased delays by up to 24.0%, while converting to a DDI reduced delays by up to 60.6% compared to the SPDI. The DDI consistently outperformed the other designs, reducing queue lengths by up to 48.4% and stops by up to 45.2% relative to the SPDI. Conversely, the CDI increased queue lengths by up to 82.1% and stops by up to 23.1% compared to the SPDI. Statistical analysis confirmed these differences were significant (p < 0.01). The study concludes that while CV technology offers modest improvements in mobility, the choice of interchange geometry is the dominant factor in operational performance. The DDI emerges as the superior design for reducing delays, queues, and stops, even in environments with high CV penetration. These findings suggest that transportation planners should prioritize unconventional designs like the DDI for congestion mitigation, as their benefits outweigh the incremental gains provided by CV implementation alone.

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• v2x connected vehicle