A review of capacity modelling techniques for large multi-lane roundabouts with weaving

Multi-lane characteristics in large roundabouts promote driver lane choices, causing an interaction between entry and circulating flows called weaving. Weaving affects roundabout capacity significantly as the entry rate reduces when vehicles interact with more conflicting flows. Thus, the inclusion of weaving in the capacity analysis is essential. This paper first discusses large roundabouts and performs a literature review on existing roundabout capacity modelling techniques. From there, the paper investigates current techniques to estimate the capacity for large multi-lane roundabouts from viewpoints of their capability in evaluating the capacity of large roundabouts, limitations, possible applications of simulation and machine learning in modelling large roundabouts, and modifications from the freeway weaving section. This review shows that current techniques are inappropriate for large multi-lane roundabouts with weaving for two reasons: (1) techniques mainly were introduced and applied for roundabouts with inscribed circle diameters of less than 100 meters; (2) techniques adopt multi-lane circulating streams as a total flow. This simplification cannot capture possible weaving between two streams, which significantly impacts the capacity of large roundabouts due to free driver lane choices. The research identified a challenge: the absence of a capacity modelling technique for large multi-lane roundabouts considering weaving, although many large multi-lane roundabouts are available worldwide. Research should continue to propose a method to assess the capacity of large multi-lane roundabouts considering weaving.