Capacity and LOS analysis of roundabouts

Abstract

At a roundabout, the vehicles move around a central island to proceed to different newlineapproaches of the intersection. Theoretically, vehicles circulating around the central newlineisland always have priority over the vehicles entering from the approaches. Entry capacity newlineat roundabouts is defined as the maximum traffic inflow from an entry to a roundabout newlinewhen the traffic flow at that entry is sufficient to cause continuous queuing in its newlineapproach. Level of service (LOS) offers the qualitative measure of traffic flow condition newlineof roundabout, i.e. free flow, stable flow, unstable flow or forced flow. newlineMost of the operational analysis procedures of roundabouts are based on assumptions newlinedrawn from traffic data in homogenous conditions with lane discipline. The traffic in newlinemost of the developing countries like India is heterogeneous, where the vehicles have newlinevarying physical dimensions and speeds and move freely over the entire width of newlineroadway, depending on availability of space. The unrestricted movement of vehicles thus newlinemakes the lane concept and expression of flow values, based on standard lane width, newlineinvalid. These variations make it necessary to evaluate the existing guidelines for mixed newlinetraffic conditions, identify significant factors influencing the capacity and LOS of newlineroundabouts, develop more realistic models to estimate the capacity of the roundabouts newlineand provide design guidelines for the same. The modelling approaches to estimate newlineroundabout entry capacity are broadly classified into three categories: (i) Empirical newlineapproaches yielding regression models comprising of variables related to roundabout newlinegeometry, (ii) Gap acceptance theory based on parameters representing driver behaviour, newlineand (iii) Simulation of traffic through roundabout at a microscopic level. newlineGeometric factors, traffic factors and driver behaviour impact entry capacity