Review, Evaluation and Comparison of Models for Predicting Roundabout Capacity

Luís Vasconcelos, Ana Bastos Silva, Álvaro Seco, and Tiago Abreu


Roundabout, Capacity, Gap Acceptance


This paper presents a comparative review of roundabout capacity models, supported by a database of field observations at six roundabouts in Portugal. It is shown that simple, conventional methods – TRL and Siegloch – are unable to produce reliable estimates for the complete range of circulating flows. On the other hand, Hagring’s formula, combined with a new parameterization method of the headways distribution, allows the differentiation of traffic flow characteristics at both the entry and the circulating lanes, thus generating accurate estimates even on roundabouts operating under unbalanced circulating splits.

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