Optimizing Geometric Design of Standard Turboroundabouts

Previous studies have shown that existing turboroundabout design procedures, in which swept path analyses are conducted at the end of design process, contain certain disadvantages and understatements which can lead to oversized or undersized turboroundabout solutions i.e. low intersection capacity, poor traffic safety, low driving comfort and high construction costs. Within the scope of this study elements of standard turboroundabouts were designed in accordance with the design vehicle movement trajectories obtained by the swept path analyses. Reliability of the software used in these analyses was verified by the real drives at the test site. Geometric design of standard turboroundabouts was conducted with variation of following influential parameters: design vehicle; circulatory roadway radii; approach leg offset and angle value. Design approach applied in this research resulted in optimal intersection design regarding the occupation of surrounding area and the design vehicle swept path requirements. Circulatory roadway radii and approach leg offset and angle limit values applicable on this intersection type are determined, taking into account the real traffic situation. Additional practical contribution of this research lies in the ability of application of research results in revision of existing guidelines for the design of turboroundabouts, as well as in development of new guidelines in countries which still do not have their own regulations on the design of this rather new multilane roundabout type.