Model of vehicle path radius at roundabout centreModel of vehicle path radius at roundabout centre

Korlaet, Željko; Dragčević, Vesna; Šurdonja, Sanja; Tibljaš, Aleksandra Deluka - · 2019 · DOAJ

DOI: 10.14256/JCE.2318.2018

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Summary

This paper addresses the discrepancy between theoretical vehicle path models used in roundabout design guidelines and actual vehicle trajectories observed in field conditions. Current technical regulations, such as the Dutch and American models, rely on assumed geometric paths to calculate transit speeds, but these assumptions often deviate significantly from real-world driving behavior, particularly regarding safety distances from curbs and central islands. The authors aim to develop a more accurate model for the vehicle path radius at the center of single-lane rural roundabouts, specifically for vehicles moving straight through the intersection, to improve the precision of transit speed calculations and geometric design validation. The study employs field investigations on a sample of 22 straight directions across ten roundabouts with varying geometric properties. Experimental data were collected using a high-accuracy Hiper V Dual Frequency GNSS device mounted on a standard mid-size personal vehicle (Alfa Romeo 159). Three drivers with similar experience performed at least 50 passes each under free-flow traffic and stable weather conditions. The recorded vehicle paths were approximated using AutoCAD software to determine radii at the entrance, center, and exit, as well as safety distances from raised curbs and the central island. These experimental results were compared against theoretical paths derived from Croatian, Dutch, Slovenian, Serbian, American, Australian, and English guidelines. The findings reveal that theoretical radii calculated according to Dutch, Slovenian, Croatian, and Serbian guidelines are closest to the experimental path radii in the middle of the roundabout. However, the assumed safety distances in these guidelines (minimum 1.0 m from curbs) were not met in practice; experimental paths averaged 0.7 m from the central island curb, while maintaining 1.5 m and 1.7 m from entrance and exit curbs, respectively. Conversely, American guidelines provided entrance radius values closer to experimental results, though they failed to meet recommended radius lengths in three out of four cases. The study established statistically significant correlations between specific roundabout geometric elements and the vehicle path radius at the center. Based on these correlations, the authors developed a regression-based model for the vehicle path radius at the roundabout center. This model offers a more accurate representation of actual vehicle behavior than existing guidelines, which often rely on rigid assumptions that do not reflect local driving cultures or specific geometric variations. The significance of this work lies in its potential to refine transit speed models and optimize the geometric design of roundabouts, thereby enhancing traffic safety and functionality by aligning design standards with empirical evidence.

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• road geometry