Reduction in Entry Capacity of Roundabout under the Influence of Pedestrians in Mixed Traffic Conditions

Bari, Chintaman; Dhamaniya, Ashish · 2022 · OpenAlex-citations

DOI: 10.26552/com.c.2022.4.d201-d214

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Summary

This study investigates the impact of undesignated pedestrian crossings on the entry capacity of roundabouts operating under mixed traffic conditions, a scenario prevalent in developing countries like India. The research addresses a critical gap in existing traffic engineering standards, specifically noting that models from the United States Highway Capacity Manual (HCM) are unsuitable for heterogeneous traffic environments lacking lane discipline and designated pedestrian facilities. The primary objectives were to estimate roundabout entry capacity under these mixed conditions and quantify the reduction in capacity caused by pedestrian crossflows. The methodology involved field data collection from three four-legged roundabouts in India: two "base" sections in Jaipur and Trivandrum with minimal pedestrian influence, and one "non-base" section in Surat with significant pedestrian activity. High-resolution video cameras captured traffic and pedestrian flows for over twelve hours, covering peak and off-peak periods. Traffic was classified into seven vehicle categories, and Passenger Car Units (PCUs) were determined using the time occupancy method to standardize capacity measurements. The study employed the Probability Equilibrium Method (PEM) to estimate critical gaps and follow-up times, analyzing accepted and rejected gaps for various vehicle types. Statistical analysis, including ANOVA tests, was conducted to compare gap acceptance behaviors between base and non-base sections. The results demonstrated that pedestrian presence significantly alters driver behavior and roundabout performance. Statistical analysis confirmed substantial variations in accepted gaps at the Surat location compared to the base sections, indicating that pedestrians force vehicles to yield and create larger gaps in the circulating stream. The estimated critical gap for the base sections was approximately 1.58–1.62 seconds, significantly lower than the HCM standard of 4.5 seconds, reflecting the high proportion of two-wheelers in the traffic mix. The study developed a modified HCM equation to account for these local conditions. Crucially, the research established a relationship between pedestrian volume and entry capacity, finding that capacity decreased to 1841 PCU/h when pedestrian flow reached 288 pedestrians per hour. The modified model showed a mean absolute percentage error of 11.80% against field observations, outperforming the direct application of HCM standards. The significance of this work lies in its provision of empirical evidence and modeling adjustments for roundabout capacity in mixed traffic environments. It highlights that undesignated pedestrian crossings impose a measurable penalty on roundabout efficiency, necessitating revisions to capacity estimation methods in regions like India. The findings suggest that current international standards, such as the HCM, overestimate capacity in these contexts and fail to account for the complex interactions between pedestrians and heterogeneous vehicle streams. This research offers a foundation for updating local highway capacity manuals and designing safer, more efficient roundabouts that accommodate both vehicular and pedestrian movements in developing nations.

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• pedestrian behavior perception