Turbo roundabouts: geometric design parameters and performance analysis

A turbo roundabout is a particular type of roundabout where entering and circulating lanes are bounded by traffic signs and by non-mountable curbs. The physical separation between lanes, both at entries and on the ring, helps to prevent side collisions crossing the roundabout. The main advantages of turbo roundabouts are: i) reduction in the number of potential conflict points; ii) lower speed of vehicles passing through the intersection; iii) safety conditions at the intersection due to lower risk of side-by-side accidents. Also, in some cases the capacities of turbo roundabouts are higher than the capacities of conventional roundabouts. This paper presents an estimation of capacity, delays and level of service of turbo roundabouts in undersaturation conditions, considering both vehicular flow and pedestrian stream. It also examines the geometric parameters of the central island and circulating lanes in several turbo roundabout layouts.