In the last years roundabouts are being implemented in a variety of situations. Many states are considering roundabouts as viable alternative to a two-way stop-controlled intersections, and in some case , signal and complex interchanges. The success of roundabouts is explained, first, by the ideal safety conditions that this type of intersection present, and, second, by the advantages roundabouts provide in speed reduction, suitability to traffic, and beak effect. In Italy it begin to built roundabouts since eighty but often without to follow a design standards and often resorting to many personal interpretations.
Older roundabouts had a large radius and were traveled with high speed, moreover they had not always a circular shape, in contrast modern roundabouts are circular, have a small radius and are traveled with a low speed. The study focused on geometry characteristics that influence the safety and operational performance of roundabouts, for defining structural adjustment.
The central part of the analysis includes the study of the driver behaviour in the branches of entry, in the exits, and in the crossing of the ring. The driver behaviour is appraised by trajectories and practiced speed through the restitution with photogrametric techniques. The speed profiles of the drivers is compared with the geometric characteristics of the roundabout with the purpose to verify its congruence..
