Geometric Design and Safety Aspects of Roundabouts

Abstract

The findings of a 3-year study conducted at Pennsylvania State University for FHWA on the safety and operational performance and geometric characteristics of roundabouts are presented. The study focused on geometric characteristics that influence the safety and operational performance of roundabouts. Accident data (including driver testimonials) were reviewed along with videotapes developed at several roundabouts in Maryland, Florida, and Nevada. Several conclusions were drawn, including the need to improve geometric design on approaches to rural roundabouts to reduce loss-of-control accidents; the need for adequate right-of-way to properly deflect vehicles around the center island; and the need for guidance regarding operating-volume-to-capacity ratios. The findings from the study will assist planners, designers, and engineers in avoiding unnecessary safety hazards and operational failures.