Geometric design of turbo roundabouts according to Croatian and Dutch guidelines

Turbo roundabout is a specific kind of multilane roundabout with spiral circulatory roadway and physical separation of traffic lanes. This particular roundabout layout was developed in the Netherlands in the late nineties of the last century with the aim of solving capacity and safety problems that occur in standard multilane roundabouts. In this paper geometric design of turbo roundabouts is analysed. Comparative analysis of turbo roundabout design procedures described in the latest Croatian and source Dutch guidelines is made, modifications of Croatian turbo roundabout in regard to Dutch layout are presented, and advantages and disadvantages of both design procedures are discussed.