Intersection Sight Distance Requirements for Basic Turbo Roundabouts

Turbo roundabouts, emerging as a solution to conventional multilane roundabouts’ safety and operations concerns, are prevalent in Europe and are still new to North America. However, few studies and guidelines on intersection sight distance (ISD) requirements exist. This paper focuses on the basic turbo roundabouts, examines the circulatory roadway and approach design features, and develops ISD models with North American practices. The ISD requirements were identified for the vehicle approaching and entering the roundabout, which conflicts with the circulating vehicle in the circulatory roadways, and the entering vehicle at the upstream entry approach. Analytical models were developed to identify the required lateral clearance at the central island and clear sight triangles at the roundabout quadrants to satisfy the required ISD. The analyses were completed for four typical sizes of basic turbo roundabouts per Dutch design criteria. The design guidelines are provided for the required lateral clearance at the central island and the required clear sight triangles at the roundabout quadrants. They would be beneficial in establishing landscaping restrictions and determining the roadway right of way and property impacts at the intersections during the roadway planning stage.