Research notes : adjustment of driver behavior to an urban multilane roundabout.

NHTSA · 2007 · ROSA P / Oregon. Dept. of Transportation. Research Unit

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Summary

This study evaluates driver adaptation to the first multi-lane urban roundabout in Oregon, constructed in Springfield in June 2006. The roundabout replaced a signalized ‘T’ intersection, prompting an investigation into how motorists adjusted their behavior to the new traffic control device. The research aimed to test two primary hypotheses: first, that speed variability on approaches to the intersection would decrease compared to the previous signalized intersection, and second, that the high incidence of driving errors observed during the initial weeks of operation would diminish over time as drivers gained familiarity. The methodology involved measuring traffic speed and variability using standard road-tube instruments at three specific locations: a single lane on Hayden Bridge West and two lanes on northbound Pioneer Parkway. Data was collected before and after the roundabout’s construction. Additionally, researchers conducted eight on-site observation sessions over a six-month period to quantify driver errors in two specific areas identified during the first week of operation as sites of confusion. These areas included westbound Hayden Bridge Road, where drivers in the right lane often made abrupt lane changes within the roundabout to avoid exiting, and eastbound Hayden Bridge Road, where drivers performed late merges across solid white lines. The results indicated that mean traffic speeds increased by an average of 4.5% across all three tested locations. However, the impact on speed variability was mixed and did not consistently support the hypothesis of a smoothing effect; one lane showed decreased variability, one showed increased variability, and the third was inconclusive. The authors suggest that factors such as the predominance of left-turning traffic and the need for lane planning may have influenced these outcomes. Regarding driver behavior, the study found a steady decrease in driving errors. Specifically, the percentage of vehicles incorrectly using the right-hand entry lane on Hayden Bridge Road dropped from an initial high of 40% to 3.3% six months after opening. This reduction in errors followed a logarithmic learning curve, indicating rapid adaptation. The study concludes that while the roundabout did not consistently reduce speed variability, drivers rapidly learned to navigate the complex intersection, significantly reducing confusion and errors over time. The findings suggest that although careful design is crucial for long-term efficiency, motorists can quickly adjust to multi-lane roundabouts despite initial challenges. The research underscores the value of roundabouts in managing traffic flow safely and aesthetically, provided that drivers are given time to adapt to the new navigation requirements.

Key finding

Improper right-lane entry maneuvers fell from as high as 40% of vehicles initially to 3.3% six months after the roundabout opened, while mean approach speed rose about 4.5%.

Methodology

field_study

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

Topics

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• work zones
• intersection design
• traffic density

Information type

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• Empirical Findings: behavioral performance data