Review of fastest path procedures for single-lane roundabouts

Good safety performance, improved capacity, and numerous environmental benefits of modern roundabouts, in respect to signalised and stop-controlled intersections, have led to their rapid implementation on road traffic networks around the world. A well-designed roundabout reduces vehicle speeds upon entry and achieves smooth speed profile by requiring vehicles to negotiate the roundabout along a curved path. With that in mind, roundabout geometric design must include prediction of entry and circulation speed by estimating the fastest path into and through the circulatory roadway. Despite the fact that overall roundabout performance depends on the quality of the design features, inconsistencies in design standards and practices concerning the aforementioned performance check can be observed. In this paper, various fastest path analysis procedures for single-lane roundabouts (described in several European and US standards and guidelines) are presented, and the diversity of the approaches is pointed out.