The capacity of conventional concentric double-lane roundabouts is only 25% higher than that of single-lane roundabouts because the inner lane is used much less than the outer lane. A multi-lane roundabout with an innovative spiral design, known as the turbo roundabout, has been developed and implemented in the Netherlands. Existing analytical models that could be used to estimate the capacity of such roundabouts are reviewed to identify the main differences between them. The Multilane Roundabout Explorer model,developed for use in the Netherlands, is based on a modification of the model derived by Bovy (1991) since the latter takes pseudo conflict (a relevant factor in Dutch traffic analysis) into account. However, this model cannot handle the stream split over the lanes of the roundabout well. On the other hand, gap-acceptance models do not take the pseudo conflict into account at all. A sophisticated approach has therefore been developed to enable these models to be used to analyze traffic situations where pseudo conflicts are involved. Finally, the parameters needed to tailor VISSIM micro simulation software for this purpose were estimated. It is concluded that a VISSIM model may be suitable for the analysis of both single-lane and two-lane roundabouts. The article ends with some noteworthy conclusions. It is hypothesized that the traffic flow rate influences the estimated critical gap. From a more practical point of view, the form of the capacity functions, the influence of speed on the critical gap and the influence of the lane-use split on the entry capacity are estimated
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