Geometry of the roundabouts

A modern roundabout can be defined as an intersection with raised central island and a circulatory roadway at which yield-at-entry rule is applied. Due to the yield-at-entry rule, an appropriate sight distance must be ensured to enable a driver entering the roundabout safely, to note on time the position of the vehicle with the right of way and to have an obstructed view of the opposite exit. In this talk we will present some of the geometry of the roundabouts referring to the as paraboloids concerning the sight distance as development of a geometric model that aids in the roundabouts central island design by determining the maximum size of the visibility obstacle.