Most transportation engineers around the world, and now in the United States, are relatively familiar with roundabouts and their operational and safety benefits. Although roundabouts are becoming increasingly common, drivers and even engineering professionals often contend with mixed messages about roundabout design and operation. In a world speckled with all manner of spiral roundabouts, signalized roundabouts, traffic circles, gyratories, and rotaries, is it any wonder that confusion, and public resistance, often persists? These mixed messages may represent the greatest hurdle to implementation, public acceptance, and safe operation of multi-lane roundabouts in particular. Within North America and across the globe, circular intersection designs that appear relatively similar to users can in fact require significantly different driver behaviors, depending on whether they are configured with a continuous circle road or a network of crossing roadways. This distinction can be of critical importance for roadway designers and agencies, elected officials and other policymakers, road user education and licensing, traffic enforcement, mapping and GPS navigation, and safe operation of autonomous vehicles. This paper aims to provide an overview of existing definitions, explore the nature of conflict points for each design, provide a framework modeling method for analysis, and provide globally applicable definitions for roundabout features for use in design, education, policy, enforcement, and research. This paper is focused primarily on roundabout design guidance and operations within the United States, but places these practices within the global context, such that the definitions and analyses provided can be applied to all forms of roundabout intersections around the world.
