Speed Analyses of Intersections Converted to Roundabouts – Case Study from Croatia

The reconstruction of standard at-grade intersection into roundabout is very often motivated by the need to improve the safety of a part of the road network. To assure the effect of the reconstruction before-after analyses based on traffic accidents or some other indirect traffic safety parameter is needed. This paper presents a detailed analysis of four roundabouts reconstructed from the at-grade intersection according to the Croatian Guidelines for Roundabout Design. The analysis included a comparison of speeds at the location - a standard intersection- before and a roundabout – after reconstruction, time distribution of operational speed and applied design elements as well as their correlations. Experimentally gathered data on operational speed showed that the expected effect of speed reduction was not achieved in most of the analyzed cases. The conclusion is that given that the Croatian Guidelines set a very wide range for roundabout elements, the designer has a great influence on the selection and, consequently, on the effects of the roundabout implementation. The revision of the Guidelines is suggested.