Non-standard roundabouts: analysis of problems

Road intersections are dangerous places in the road system due to the high number of conflicting points between motorized and non-motorized vehicles. In the case of defined traffic volume, several research groups have proven that roundabouts reduce the number of injuries and fatal accident cases. In the last years, several studies have investigated the performance of roundabouts, among which, include different models with the ability to calculate the entering flow (Qe) as a function of the circulating flow (Qc). This research work has focused on an analysis of the performance features of Italian urban roundabouts, that have non-standard geometric characteristics. The goal of the research work is to analyze, on the basis of geometrical and design parameters, the capacity of the "non-standard roundabouts" in order to understand in which way non-standard features influence capacity. The study underlines that in standard roundabouts the entering flow is reduced when the circulating flow increases (like in the existing international models) and in non-standard roundabouts the entering flow is not reduced when the circulating flow increases (it seems that there is not a relationship between circulating flow and entering flow)