Study of vehicle speed in the design of roundabouts

Some roundabout design elements significantly influence the vehicle driving speed, i.e. the trajectory of vehicles at roundabouts, which is directly responsible for the level of service and traffic safety at roundabouts. An "in situ" speed, taken as a significant roundabout-design element, is analysed in the paper using as an example four urban single-lane roundabouts located in the City of Zagreb. The American method and the Australian method are used for the definition and verification of the design speed at roundabouts. Results obtained show correlation between the design speed and the actual vehicle speed measured at roundabouts