A MESOSCOPIC APPROACH TO CAPACITY AND DELAYS EVALUATIONIN UN-SIGNALISED ROUNDABOUTS

The paper refers to the estimation of roundabout’s performances. The evaluation of un-signalised intersections and in particular the evaluation of the multi-junction ones is actually a very troublesome task. The Department of Civil Engineering of the University of Trieste has proposed a methodology to dynamically estimate the merge-area capacity for on-ramp freeway junctions. The evaluation of roundabouts is, at now, an open problem; many approaches have faced the problem of entry capacity and delays estimation, but a common and universally accepted procedure does not exist. Some suggestions recently developed on the scientific literature have stressed on a specific point: a roundabout has neither to be considered nor modelled as a simple succession of T-intersections. On congested facilities or under very unbalanced flows, a roundabout should be considered as a multi-junction node. In addition, the facility has to be considered as a multi-junction node also because of the particular relationship between the entering and the circulating flows; in fact, the vehicles which could enter into the roundabout depend on the circulating ones, which are the result of entered vehicles in the previous entry legs: the solution of this problem needs an iterative process but a final equilibrium solution could be found out.