Turbo roundabouts minimize weaving conflicts by introducing raised lane separators within the circulating lanes compared to conventional multi-lane 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 aimed to analyze driver behavior and evaluate 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 lane-change model revealed that lower vehicle speeds on circular lanes, light vehicle types, and more significant headways between vehicles contributed to lane-change events. The speed choice model revealed that lower approach speeds, heavy vehicle types, left-turn movements, and smaller circular lane radii all resulted in reduced vehicle speeds on circular lanes. Observed critical gaps (4.4 to 5.8 seconds) were higher than in traditional multi-lane roundabouts (4.5 to 5.3 seconds). Follow-up time (3.7 to 4.7 seconds) was also higher than that of traditional multi-lane roundabouts, as drivers merged more cautiously in the circulating lanes due to the raised lane dividers within the circular lanes. Drivers on the turbo roundabout's inner lane exhibited longer critical gaps than those on the outer lanes due to relatively complex merging events on the inner lanes, such as crossing multiple lanes to merge into the inner circulating lane. 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 primarily caused by improper lane changes and failure to yield. The turbo roundabout substantially lowered crash severity and eliminated speeding-related crashes. Seventy-six percent (76%) of post-installation crashes were attributed to unfamiliarity and right-of-way violations, while 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. This research contributes to a broader understanding of turbo roundabout performance in the US. Findings can be used to refine design, capacity, operational, and safety analyses based on driver behavior in the US.
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