Modelling the capacity of a traffic circle with respect to the effect of delays in the circulating area

This study discusses capacity models, delay in the circulating area and its effect on roundabout capacity. Firstly, an overview of the roundabouts and capacity models is presented. As a result of the study on capacity models; for empirical model and gap acceptance model; because the drivers don't obey the rules about reverse and limited priority conditions; results are not satisfactory and when pedestrians and bicyclists are also considered; applicability of the methods are even less, we try to adopt additive conflict flow (ACF) model to our country. After evaluating the methodologies proposed in early studies we suggest a new formulation for capacity calculation for the further develope and improve of ACF model. Also, a new α formulation and an Aij formulation based on field observations, at five roundabout sites in the city of Izmir, are proposed in this study. Field data, values of proposed formulation results of this study are then compared with those values calculated by other formulations; values obtained as results of the proposed formulation are found to be in accord with those of the field data. At final part of the study; we mention there might be delay in the circulating area under limited priority case, when the drivers on minor stream force the drivers on major stream to slow down or stop and reverse case, when the minor stream have a higher traffic volume than major stream and analyze its effect on roundabout capacity.