Recent Evolutions of Roundabouts: Methodological Issues and Practical Concerns.

Abstract

The aim of the research is to provide a choice criterion between innovative roundabouts (turbo-roundabouts and flower-roundabouts) and double-lane roundabouts by evaluating convenience in terms of performances, when traffic demand is known. For this purpose, comparisons of operational performances at innovative roundabouts with regard to those at traditional roundabouts were developed. We started from consistent assumptions regarding the arrival process of major streams and used capacity models founded on gap-acceptance theory. Having in mind a bunched exponential headways distribution, we proposed adaptations of the Hagring model for estimating entry capacity at intersections under examination, where movements with only one or two conflicting traffic streams can be observed. Suitability domains (or indifference areas) were obtained using as comparison criterion the control delay since it is related to the level of service quality. Results provide some evidence of convenience or not in choosing a turbo-roundabout or a flower roundabout rather than a double-lane roundabout, both for new installations and for conversion of existing roundabouts