Conflicts between capacity and safety in roundabout design : a case study.

The introduction of small island roundabouts has enabled junctions of greater capacity than conventional layouts to be achieved within a given land area. However, it has become apparent that the capacity gain is often accompanied by an increase in accidents. The authors will detail a case study where a congested conventional roundabout was converted to a small island layout, and where that layout was itself subsequently modified in an attempt to reduce a significantly increased accident record. Drawing from the experience of this, and other roundabout sites in Kent, the authors will comment upon the importance of design factors such as approach speed and deflection, relating their conclusions to the current DTP design memoranda.(a) for the covering abstract of the proceedings see IRRD 274491.