Roundabouts are very often implemented as a measure for speed control at the intersections where there is a problem with traffic safety. Although the approaching speed is emphasized in some research as relevant for operational speed in the roundabout, there are no detailed analyses of the effects of geometric and traffic elements on approaching speed that can be used to design safer roundabouts. The experimental study presented in this paper was done on six different roundabouts, on 22 approaches, located at a regional road network. The outer radii of analyzed roundabouts were from 15 to 22 m. The speed was measured for 24 hours at every approach. As operational speed, v85 - speed up to which 85% of vehicles are moving was included in the analyses. The impact of main geometric elements – lane width, slope, and length of the straight part of the road before entrance to the roundabout was analyzed. As a traffic parameter, the impact of the posted speed limit at the approach on the operational speed was also analyzed. Some preliminary recommendations regarding speed control were generated as a conclusion of this study.

roundabout, speed, approach