Mini-roundabouts have been used extensively at urban junctions since their introduction in the early 1970s. They have central islands of up to 4m in diameter, which have no street furniture and are capable of being driven over; they are generally subject to a 30mph speed limit. Although national accident totals at these junctions are relatively low at about 1400 per year, the number of mini-roundabouts is increasing rapidly as traffic calming becomes more widespread, and their safe design is therefore important. This paper reports on the results of a study commissioned by the Road Safety Division of the Deaprtment of Transport and undertaken by the Transport Research Laboratory with the Transportation Research Group at the University of Southampton as a sub-contractor. It is one of a series investigating accidents at different junctions and link types. A stratified sample of 200 3-arm and 100 4-arm mini-roundabouts was identified. Extensive data collection was carried out at these junctions, including 12 hour vehicle and pedestrian counts and a geometric survey. Accident records were obtained for all reported personal injury accidents occurring at the junctions from 1986 to 1992. The main objective of the study was to relate accident frequency by main accident group to traffic flow, road features, geometry, land-use and other explanatory variables using the technique of generalised linear modelling. The resulting models are intended to be used to identify potential design improvements and to provide accident estimates for the economic appraisal of road improvements. They can also be used in conjunction with traffic assignment models.
Abstract