An Operation and Safety Assessment Study of Roundabout Types

PURPOSES: The aim of this study is to analyze and compare the operational effectiveness and safety of three different types of roundabout found in the literatures using a VISSIM and SSAM program. METHODS : The three types roundabout tested are the 2-lane roundabout (2R), the Turbo roundabout (TR), and the Flower roundabout (FR). For each scenario, three roundabout types and traffic conditions such as traffic volume and movement ratio were applied to VISSIM in order to compute the average delays. In addition the total conflict was calculated through SSAM by using trajectory data from VISSIM. RESULTS: From the analysis results, the average delay in TR and FR type was higher than the 2R. Regardless of the roundabout types, the average delay was reduced as the right-turn vehicles increased. The total conflict in TR was fewer than 2R for all traffic conditions. CONCLUSIONS : The results of this study can be used in the planning and design process of roundabout deployment. The data also provides some numerical justifications in transition from at-grade intersection to roundabout.