This paper summarises the work undertaken in a study titled 'Relationship Between Roundabout Geometry and Accident Rates', in which data on geometry, traffic volumes and accidents were collected and analysed for one hundred Queensland roundabouts. From this data, five major accident types were identified, with predictive equations developed for each using a generalised linear model with a Poisson error distribution. During the analysis of this data, it was found that the most significant equations were developed by selecting parameters for trial, based on the known or expected behaviour of drivers involved in accidents. The predictive equations are given in the paper, together with design considerations to minimise rates of each accident type. The most important geometric parameters found were approach curvature, central island diameter, decrease in speeds between successive horizontal geometric elements, separation between legs and length of horizontal geometric elements. Following this summary, the paper then discusses the program ARNDT - 'A Roundabout Numerical Design Tool'. This tool enables designers to predict accident rates and costs for new or exiting roundabouts, by utilising the results of the roundabout study. The ARNDT program was developed to avoid the many tedious manual calculations that would otherwise be required to determine some of the input parameters. It is a useful tool for determining the potential safety performance of a roundabout, by identifying potentially hazardous geometry. It can be used to determine the likely saving in accident costs by the adoption of particular geometric treatments. (a)
Samenvatting