Roundabout System Capacity Estimation and Control Strategy with Origin-Destination Pattern

Abstract

This study investigates the roundabout as a system in which the interaction of inflow, outflow, and circular flow are analyzed. Developed based on the concept of Macroscopic Fundamental Diagram (MFD), the macroscopic properties of the roundabout system are estimated by fitting traffic data into several traffic-stream models. The capacity and optimal density are derived from regression fitting. A novel control strategy that aims to regulate the approach inflow in order to maintain the average density on the circular segment at an optimal density is then proposed. It decides on the approach that needs to be restricted based on the circular segment density (i.e., congestion level) and the origin-destination demand pattern to prevent gridlock. A case study of a two-lane roundabout in Selangor, Malaysia is developed in a microscopic simulation environment to study the roundabout system properties and to test the effectiveness of the proposed control strategy. Results show that the Greenshield model has the best fit in describing the roundabout system properties. The proposed control strategy is effective in reducing system travel time and increasing throughput, especially during medium to high levels of demand. In addition, the sensitivity analysis reveals that the effectiveness is sensitive to the parameter setting, roundabout geometry, as well as traffic condition and origin-destination pattern.