Roundabouts are a popular choice for intersection control around New Zealand, particularly for replacing priority controlled intersections where traffic volumes are high and safety has deteriorated. However, safety problems can occur at poorly designed roundabouts, particularly where speed is not managed well and where cycle volumes are high. Despite their generally good record, safety deficient roundabout designs have received considerable attention from safety auditors over the last 10 or so years. This culminated in the publication of the guide The ins and outs of roundabouts. This guide lists problems encountered in 50 safety audit reports. The guide lists visibility and geometric design features, particularly inadequate deflection and marking, as problem areas. The guide states that ‘the safe and efficient movement of traffic relies on good unobstructed lines of sight’. The provision of good visibility at roundabouts follows the guidance in the Austroads Guide to traffic engineering practice part 6: roundabouts. This practice, which occurs in New Zealand and Australia, differs to practice in other parts of the world, particularly Europe, where visibility is often restricted to reduce speeds and improve safety. This discrepancy was a major motivator for this research project. While roundabouts often have better safety records overall when compared with other forms of control, they have a poor safety record with respect to cyclist crashes, particularly at large roundabouts with multiple lanes. This higher cycle crash risk at larger and medium roundabouts is probably caused by higher motor vehicle speeds, resulting in a larger speed differential between cyclists and motor vehicles. In addition, the increased complexity of negotiating multi-lane and high-speed roundabouts could be a reason why some drivers do not see cyclists. This study, undertaken in 2006, aimed to investigate these issues by focusing on the relationship between crashes, speed, traffic volume and sight distance for various approach and circulating movements at roundabouts. This research extends on previous work into flow-only crash prediction models developed in New Zealand by including key non-flow variables. Given the impact vehicle speed is expected to have on the ‘active’ modes (walking and cycling) as opposed to the impact on motorised modes, separate models have been developed for crashes involving these modes. Future research will examine the impact that geometry has on various crash types. (Author/publisher)
Samenvatting