As small roundabouts are becoming an increasingly popular type of at-grade intersections, researchers are encouraged to study new computational methods and carry out comprehensive studies of small roundabouts performance.Some aspects of their operation are of special interest, i.e. their operation in a situation of changes of the dominant flows throughout the day, possibility of certain increase of the capacity of one-lane small roundabouts without necessity of building a two-lane roundabout or other type of intersection and also an impact of small roundabout geometry on traffic safety, represented in an indirect way by the impact on speed on its consistency. The paper presents results of analytical study (first case) and empirical studies of two other issues. Small roundabouts became very fashionable. Decisions on their construction instead of other intersection type are made without sufficient traffic analysis, which is indispensable, particularly at large variations of size and directional composition of traffic flows as well as in the cases of predicted demand flows close to capacity. The paper presents analytical study of the first issue and a model of capacity of a right-turn bypass used on several Polish roundabouts that can carry large right-turn movements. The last part presents results of empirical studies of operating speed of vehicles negotiating a roundabout and analyses of impacts on speed of such design elements as: inscribed circle diameter, widths of approach, entry, circulatory roadway and exit as well as entry and exit radii.
Abstract