Speed Control at Roundabouts - use of Maximum Entry Path Radii

Abstract

This paper proposes a method for speed control at roundabouts based on setting maximum values of entry path radii for roundabouts, in lieu of the deflection criteria used in the current Austroads (1993) roundabout guide. The proposed method uses the results of a Queensland study of roundabouts. The aim of the Austroads (1993) method is to control speeds through roundabouts by the provision of 'deflection', which is measured as a maximum vehicle path radius of 100m through the circulating carriageway. This method of speed control is based on 1975 design recommendations by the UK Department of the Environment. The current practice in the UK Department of Transport 'Design Manual for Roads and Bridges' provides speed control on the entry curve in lieu of the circulating carriageway. USA and Queensland also have criteria for speed control through roundabouts. This includes setting maximum values of the vehicle speed on the entry curve (and subsequent entry path radii). No mandatory speed control criterion is given for the circulating carriageway.