Modeling of a novel risk index for evaluating the geometric designs of roundabouts

Abstract

In the geometric design of roundabouts, safety-oriented approaches are required rather than specification design ones that simply determine the dimensions of the geometric structural elements. We herein propose a risk index (RI) that combines the invisibility probability and the crash impact as a performance measure for evaluating the safety of the geometric designs of roundabouts, and we also describe a method for calculating this index. Invisibility probability represents the probability that an entering vehicle cannot view a vehicle coming from the upstream in a circulatory roadway and crash impact represents the amount of lost kinetic energy at the time of collision corresponds to the impact of the crash. A numerical simulation to model this RI on the basis of various geometric conditions is further presented. It is demonstrated that the invisibility probability is large when the entry angle is small and that the crash impact increases when the deviation angle decreases. The proposed approach is expected to help resolve issues with currently existing roundabouts and improve the design of future roundabouts to enhance their safety performance.