Influence of Intergreen Times on the Capacity of Signalised Intersections

Wolfermann, Axel · 2009 · OpenAlex-citations

DOI: 10.26083/tuprints-00001962

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Summary

This dissertation investigates the influence of intergreen times—the intervals between the end of one signal phase and the start of the next—on the capacity of signalized intersections. The research is motivated by the observation that while intergreen times are essential for safety, their duration is often determined using inconsistent international parameters and excessive safety margins. This leads to a significant gap in understanding the precise capacity impacts of these intervals. The study aims to develop a methodology to calculate effective capacity, quantify the potential for capacity improvement through optimized intergreen times, and identify measures that enhance throughput without compromising safety. The methodology combines a comprehensive theoretical analysis with empirical validation. Due to the complexity of driver behavior, the primary focus was on developing a transparent, flexible theoretical model to analyze traffic flow processes during signal change intervals. This model accounts for intersection layout, signal programs, and stage settings. To validate the model and quantify capacity impacts, empirical data were collected from seven urban intersections in Germany using video observations and speed measurements. The study compares the model’s outputs against standard capacity manuals, including the German Highway Capacity Manual (HBS) and the U.S. Highway Capacity Manual (HCM). The findings reveal that effective green times at the surveyed intersections are greater than signaled green times, as vehicles utilize part of the intergreen interval to enter the intersection. At an example intersection, the effective capacity was found to be 5% higher than calculations based on signaled green times and saturation headways, and 7% higher than estimates provided by the HBS. The research identifies that prevailing intergreen calculations are often longer than theoretically required due to ignored parameters (such as entering times), irrelevant conflict scenarios (e.g., low-volume turning traffic), and added safety margins. The study quantifies the capacity improvement potential, attributing up to 50% of the potential to "conflict difference times" where calculated conflicts do not effectively occur, and approximately one-third to the neglect of significant entering times under saturated conditions. The significance of this work lies in providing a detailed description of traffic flow during signal changes and a model to determine effective capacity and optimization potential. It concludes that many capacity reductions caused by intergreen times lack clear safety justifications. Recommendations include analyzing influencing factors to predict parameters more precisely, thereby reducing the need for large safety margins, and optimizing signal programs and intersection layouts to minimize parameter variation. The study suggests that future research should focus on the interrelation of yellow time and crossing times to achieve simultaneous improvements in safety and capacity.

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