Determination of Mini-Roundabout Capacity in the United States

Abstract

The design of mini-roundabouts has been around and practiced in Europe for decades. It has been a successful and low-cost intersection configuration using existing external boundaries of intersections. Nevertheless, accessible traffic capacity models for mini-roundabouts do not exist. This study provides design recommendations and a simulation approach for capacity models of mini-roundabouts from U.S. data. Two geometries are selected that have a 7 or 10 m (24- or 36-ft) approach width typical of conventional intersections. The mini-roundabouts are best defined by the inscribed circle diameter of 15 and 23 m (50 and 75 ft). Field data are collected on drivers’ behavior and decisions for a mini-roundabout design in order to calibrate simulation models. A microscopic traffic simulation software is used to model the selected prototype designs for capacity estimations. The defining feature for mini-roundabouts is the traversable central and splitter islands for large vehicles that make through or left-turn movements. The linear regression models presented estimate the capacity of the mini-roundabouts to be lower than that of the single-lane roundabout. However the mini-roundabout has a higher capacity per square foot of land, which would be an innovative solution for urban areas for increasing capacity at existing all-way stop-controlled intersections at lower cost than single-lane roundabouts.