Conversion of existing roundabouts into turbo-roundabouts: case studies from real world, Journal of Civil Engineering and Architecture 6(8)

Compared with roundabouts the main advantages of turbo-roundabouts are the reduction in the number of potential conflicting points and the lower speed of vehicles through the intersection; they both can improve road safety conditions at the junction. Moreover, the physical delimitation among lanes limits the side-by-side accident risk. These aspects make turbo-roundabouts more appropriate than roundabouts when a higher level of safety has to be guaranteed, particularly in presence of relevant pedestrian and two-wheels traffic volumes. The present paper has three main objectives : 1) to discuss general design criteria and functional principles of turbo roundabouts; 2) to give the geometric design principles of the central island and circulating lanes; 3) to present three case studies from real world concerning the conversion of existing roundabouts into turbo roundabouts.