Turbo roundabouts:geometric design parameters and performance analysis

A turbo roundabout is a particular type of roundaboutwhere entering and circulating lanes are bounded by traffic signsand by non-mountable curbs. The physical separation betweenlanes, both at entries and on the ring, helps to prevent sidecollisions crossing the roundabout.The main advantages of turbo roundabouts are: i) reduction inthe number of potential conflict points; ii) lower speed of vehiclespassing through the intersection; iii) safety conditions at theintersection due to lower risk of side-by-side accidents. Also, insome cases the capacities of turbo roundabouts are higher thanthe capacities of conventional roundabouts.This paper presents an estimation of capacity, delays and level ofservice of turbo roundabouts in undersaturation conditions,considering both vehicular flow and pedestrian stream. It alsoexamines the geometric parameters of the central island andcirculating lanes in several turbo roundabout layouts.