Evaluating Driver Behavior in Navigating Rotor Turbo Roundabout Features and Intersection Safety Performance

Turbo roundabouts minimize weaving conflicts by introducing raised lane separators within the circulating lanes compared with conventional multilane roundabouts. Although widely used in Europe, turbo roundabouts are relatively new in the US. The California Department of Transportation (Caltrans) installed a rotor turbo roundabout in San Benito County in 2024. This research analyzed driver behavior and evaluated safety performance at this newly built turbo roundabout by performing descriptive analysis and statistical modeling. Approximately 5% of vehicles made prohibited lane changes within circular lanes, particularly during left-turn movements. The factors affecting the prohibited lane-change model indicate that lower vehicle speeds on circular lanes, light vehicle types, and vehicle headways are significantly associated with the likelihood of lane-changing events. The speed choice model indicated that lower approach speeds, heavy vehicle types, left-turn movements, and smaller circular lane radii reduced vehicle speeds on circular lanes. An early traffic analysis applying the extreme value theory (EVT) captured the relationship between conflict estimates and observed crashes. Based on average post encroachment time (PET), extreme conflicts were caused primarily by improper lane changes and failure to yield. The turbo roundabout substantially lowered crash severity and eliminated speeding-related crashes. A total of 76% of postinstallation crashes were attributed to unfamiliarity and right-of-way violations, and 22% were due to navigational errors. These findings underscore the need for improved dissemination of proper turbo roundabout driving information and appropriate signage to facilitate safe lane selection and prevent prohibited lane changes within circulating lanes. The findings of this study contribute to a broader understanding of turbo roundabout performance in the US and can be used to refine design and safety analyses based on driver behavior in the US.