THE CONVERSION OF A CONVENTIONAL TO A SMALL ROUNDABOUT

A conventional roundabout with a central island diameter of 27 M had become congested at peak periods and was replaced with a small roundabout having a central island diameter of 8 metres. Within 6 months of its installation, some operational shortcomings of the small roundabout were obvious, and substantial changes were made to the road markings. Surveys were then undertaken for a before and after comparison of traffic volumes, delays and safety. A proposed before and after comparison of the small roundabout with traffic signals at the same intersection was abandoned when it was decided to retain the small roundabout permanently, as its success exceeded expectations of the road controlling authorities. Queue lengths and delays during peak periods reduced dramatically after the installation of the small roundabout. The increase in traffic volumes was restricted by the inability of the adjacent intersections and roads to feed sufficient traffic to the approaches of the small roundabout to enable it to reach capacity. The before and after analysis of accidents failed to establish that a statistically significant change in accident rate had occurred. (a) (TRRL)