Some common and differing aspects of alternative models for roundabout capacity and performance estimation

This paper considers three well-known analytical models of roundabout capacity, and discusses some common and differing aspects of these models. The models considered are the US Highway Capacity Manual 2010 (HCM 2010) model, Australian SIDRA INTERSECTION model and the UK TRL (linear regression) model. These models have some common features as well as significant differences. A detailed table comparing the features of these capacity models is presented. The UK TRL and SIDRA models are compared in relation to several geometric parameters (entry radius, entry angle, inscribed diameter and flaring). Detailed comparison of estimates of capacity and degree of saturation (v/c ratio) produced by these models are presented for a multi-lane roundabout example. The aim of the paper is to enhance understanding of the fundamental aspects of different roundabout capacity models available around the world.