Study of driver behaviour at turbo-roundabouts

Chodur, Janusz; Bąk, Radosław · 2016 · DOAJ

DOI: 10.5604/08669546.1218790

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Summary

This study investigates driver behavior at turbo-roundabouts, a specific type of multi-lane intersection designed to eliminate weaving maneuvers through spiral lane layouts. The research was motivated by the increasing adoption of turbo-roundabouts in Poland, where the absence of uniform design guidelines has led to varied geometric solutions, particularly regarding the method of separating traffic lanes. The primary objective was to determine how different lane separation methods—specifically raised physical dividers versus horizontal marking only—influence driver compliance with traffic rules and vehicle speeds. The researchers conducted field measurements at seven turbo-roundabouts in Poland, selected for their geometric diversity and varying lane separation methods. Data collection involved a monitoring system using multiple cameras to record video footage of traffic flows. This footage allowed for the reconstruction of vehicle trajectories and the estimation of instantaneous speeds at five specific sections: the approach, entry, conflicting area, circulatory roadway, and exit. The study categorized driver behavior into correct lane usage and various improper behaviors, such as encroaching on lane edges, illegal lane changing, and driving over solid lines. The findings indicate that raised lane dividers significantly improve driver compliance with designated traffic corridors. In roundabouts with physical separation, instances of driving over lane edges were practically eradicated, whereas roundabouts relying solely on horizontal marking exhibited higher rates of encroachment and illegal lane changing. Specifically, fewer than 20% of light vehicles in unseparated lanes encroached on neighboring lanes, while some drivers ignored markings entirely. However, physical separation did not eliminate all improper behavior; illegal lane changing still occurred, particularly at entries and exits, with the highest frequency observed in Stalowa Wola (45% of inner lane exits). Regarding speed, vehicles encroaching on neighboring corridors traveled visibly faster than compliant drivers. In roundabouts without physical dividers, the mean speed in the circulatory roadway was 35 km/h, compared to 27 km/h in those with dividers. Additionally, the speed difference between inner and outer lanes was greater in unseparated roundabouts (approx. 10 km/h) than in separated ones (approx. 3 km/h). The study concludes that while raised dividers enhance safety by restricting illegal lane changes and reducing speeds, they do not completely prevent improper maneuvers. Using crash prediction models, the authors estimate that lane dividers may reduce the number of crashes by 10% to 17%. The results suggest that physical separation is a more effective safety measure than horizontal marking alone, though geometric factors such as roundabout diameter and deflection angles also influence driver behavior and speed. These findings provide empirical evidence to support the development of standardized design guidelines for turbo-roundabouts.

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Topics

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• intersection design
• perceptual countermeasures