Models for estimating the capacity of roundabouts

Roundabouts, as a special form of unsignalised intersections, are an increasingly common choice of designers around the world. Adjusting the capacity of roundabouts with flow requirements is one of the most important steps in order to meet the planned traffic conditions. The capacity of roundabouts can be determined by empirical methods, by the methodology of gap acceptance and by simulation. Each of these methodologies has some limitations, because none of them can independently and fully take into account the complex processes of driver behaviour, as well as the kinematic processes that occur at the entry flows of roundabouts. All of these models require certain semi-empirical or fully-empirical parameters that take into account local conditions that are largely dependent on driver behaviour. Although such calibration allows applicability in similar traffic conditions, it is often restricted by data availability or an incomplete understanding of the relationships between model parameters and capacity.