Simulation of the Pedestrians' Influence to the Capacity of Motorised Vehicles in a Roundabout

Tollazzi, Tomaž; Lerher, Tone; Šraml, Matjaž · 2008 · OpenAlex-citations

DOI: 10.3844/ajassp.2008.34.41

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Summary

This study addresses the challenge of accurately determining the capacity of one-lane roundabouts when significant pedestrian and cyclist traffic interacts with motorized vehicle flows. Traditional methods for calculating roundabout capacity often rely on simplifications or complex mathematical calculations that are difficult to apply in exceptional cases involving high non-motorized traffic. The authors propose a new approach using discrete simulation modeling to analyze how pedestrians and cyclists, who have priority over vehicles, influence the permeable capacity and potential blockage of roundabouts. The motivation stems from the need for a reliable tool to assess whether implementing a roundabout is reasonable in areas with strong mixed traffic flows, where vehicles must yield to pedestrians, potentially causing congestion or complete blockage. The methodology employs discrete numeric simulations using the AutoMod programming tool to model a specific three-armed, one-lane roundabout in Maribor, Slovenia. The simulation incorporates actual geometrical data, such as roundabout diameters and crossing widths, and kinematic parameters, including vehicle and pedestrian velocities and accelerations. Input data for traffic flows were derived from a 15-hour field measurement campaign (6:00 to 21:00) counting motorized vehicles, pedestrians, and cyclists on each arm. These counts were statistically evaluated and modeled using Poisson distributions for arrival rates and exponential distributions for time intervals between arrivals. The simulation algorithm enforces the rule that vehicles must stop and wait if pedestrians or cyclists are present on the crossing, simulating queue formation and waiting times. The results demonstrate that the simulation model closely matches real-world observations. A comparison between measured traffic counts and simulation outputs showed minimal discrepancies, ranging from -2.13% to 4.76% across the three arms of the roundabout. The analysis identified three distinct operational states based on pedestrian flow intensity: (1) sufficient time gaps between pedestrians allow uninterrupted vehicle flow; (2) vehicles wait in designated spaces but flow remains stable; and (3) pedestrian flow is so dense that waiting spaces are constantly occupied, causing queues to spill back onto the circulatory roadway. This spillback can block adjacent entries, potentially leading to a complete blockage of the roundabout if the congestion propagates against the direction of traffic. The significance of this work lies in providing a validated, detailed simulation tool for traffic engineers to evaluate roundabout performance under mixed traffic conditions. By modeling the specific interactions and priority rules between vehicles and non-motorized users, the approach offers a more accurate assessment of capacity reduction and blockage risks than traditional simplified methods. This enables better decision-making regarding the implementation of roundabouts in urban environments with high pedestrian and cyclist activity, ensuring that infrastructure designs account for the complex dynamics of shared road space.

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• traffic density