A Comparison of Two Roundabout Capacity Models

Abstract

This paper presents the results of a detailed comparison of two roundabout capacity models, namely a model developed by the first author of this paper based on her research conducted in Poland (referred to as the Macioszek model) and the model used in the SIDRA INTERSECTION software based on roundabout research conducted in Australia (referred to as the SIDRA Standard model due to other model options in the software). Both models are lane-based analytical models based on gap acceptance theory with an empirical basis, and both models use Cowan's bunched exponential distribution of circulating road headways. On the other hand, the two models use different capacity and headway distribution equations, and they are calibrated for different traffic conditions in two different countries. Comparisons of entry lane capacity estimates from the two models for one-lane and for two-lane roundabouts are presented. Analyses indicated that the entry lane capacities at one-lane roundabouts in Poland are lower but close to those in Australia whereas the entry lane capacities at two-lane roundabouts in Poland are much lower than those in Australia. Calibrating the SIDRA Standard model using data for 21 one-lane roundabouts and 12 two-lane roundabouts resulted in capacity estimates with very good match to driving conditions in Poland.