Modelling traffic flow at multi-lane urban roundabouts

This paper proposes Multi-stream Minimum Acceptable Space (MMAS) Cellular Automata (CA) models to study unsignalised multi-lane (two- or three-lane) urban roundabouts. Through detailed space considerations, using Cellular Automata (CA) and the Multi-stream Minimum Acceptable Space method, heterogeneity and inconsistency of driver behavior and interactions in cross traffic at entrances of roundabouts are simulated by incorporation of four different categories of driver behavior (i.e., conservative, moderate, urgent and radical), together with reassignment of categories with given probabilities at each time step. The method is able to reproduce many features of urban traffic, for which gap-acceptance models are not robust. Multi-lane roundabout models, in particular for two-lane roundabouts, are developed with different vehicle lane-allocation patterns. Various properties of multi-lane roundabout operations have been explored including throughput, turning rates, critical arrival rates and congestion. The operations of two- and three-lane roundabouts are compared in terms of throughputs. Vehicle movements in this paper relate to left-side driving, such as found in Ireland, New Zealand and the UK. However, results are generally applicable to the countries where the give-way rule is applied.