ACCIDENT PREDICTION AT URBAN ROUNDABOUTS IN NEW ZEALAND: SOME INITIAL RESULTS

Roundabouts are becoming increasingly popular as a choice of intersection control in New Zealand (NZ) due to operational efficiency and safety benefits; in particular roundabouts are used instead of priority control types such as Stop and Give Way controls. Recent revisions of Transfund’s Project Evaluation Manual (PEM) utilise accident prediction models to give a better estimate of the true accident frequency of an intersection. At present these prediction models are based solely on traffic volumes. This paper details the initial findings of research to develop more advanced urban roundabout accident prediction models that will enable more accurate evaluation of urban roundabout accident benefits. It is planned that these models will predict vehicle accidents on urban roundabouts in NZ in relation to traffic volumes and geometric variables – it is proposed that the inclusion of geo metric variables will greatly improve the accuracy of these equations. Accident prediction model forms and findings from the United Kingdom, Australia, and NZ are outlined. A considerable database has been collated including traffic movement volumes, geometric site characteristics, and accident data for 95 urban roundabouts throughout NZ. Some initial results from the database are presented and discussed. It is envisaged that these new accident prediction models based on traffic volumes and geometric layout variables will be incorporated into a future amendment of the PEM, which uses benefit / cost analyses to determine road improvement priorities in NZ.