Researching a Capacity Model for Multilane Roundabouts with Negotiation of the Right-of-Way between Antagonist Traffic Flows.

This article summarizes a research program designed to assess operating conditions through capacity estimationat not-conventional roundabouts characterized by a central island with a large diameter and by two (or more)entering and circulating lanes. Although giving priority to vehicles on circulatory roadway is the nominaloperating rule, on-field observations highlighted that in some infrastructural schemes of the type considered inthis research drivers negotiate the right-of-way according to a consensus pattern that alternates betweenantagonist traffic flows, similarly to that observed at all-way-stop-controlled intersections. Considering thepeculiarity of the way of working at roundabout schemes being examined, as well as difficulties faced in theapplication of models based on gap-acceptance theory to evaluate performances, an analytical capacity modelderived from field observations was proposed for multilane not conventional roundabouts.Drawing inspiration from the iterative procedure proposed for capacity estimates at all-way-stop-controlledintersections, a calculation algorithm organized in 5 subsequent computational steps was developed in order toevaluate capacity at each entering/circulating lane for the type of roundabouts examined in this research. Resultscompared to those calculated by models for modern roundabouts show the effect on estimates of capacity raisedby a more realistic operating pattern and indicate that the capacity model may be able to estimate parametersuseful for planning and design purposes