Calculation of turbo- roundabouts with slip lanes

A turbo roundabout is a particular type of roundabout where all lanes are bounded by traffic signs and by non-mountable curbs installed at entering and circulating lanes. Turbo roundabouts also have a very particular shape to accomplish the splitting of traffic streams and to prevent cars weaving through. 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. Only in some traffic conditions, turbo roundabouts can offer higher capacities than conventional double-lanes roundabouts, so if more capacity must be guarantee a bypass lane can be added to the turbo roundabouts layout. This paper presents a closed-form model for the estimation of capacity, delays and level of service of turbo-roundabout equipped with Right-turn bypass lanes, considering the effect of geometric slip lane schemes, control type, vehicular and pedestrian flow.