Control of traffic at a road junction by roundabout or gyratory movement, creates problems in design that are unique. The history of research on roundabouts, shows that "what is going on" is not obvious. Earlier theories and studies were influenced by the existing urban road layouts. Changes in vehicles have also had an impact. Over many years there have been different ideas about the ideal form of roundabout, with little consensus on the crucial effect of rules for negotiating the junction. Important experiments on traffic roundabouts have been carried out in the UK, during a period of some 25 years, when the verdict elsewhere on a roundabout as an efficient form of junction, was unfavourable. These studies sought, the principles of a roundabout layout which maximise traffic capacity and safety, also to develop practical design methods for the highway engineer. The accumulated results have been implemented, and refined in the UK with considerable success. This review refers to that research, tracing in considerable detail, the evolvement of roundabout design in the UK up to 1993. It also looks at the research and contemporary design practice in other countries. It contains extract from UK roundabout Design Guidelines, but does not claim to be a "designer"s manual". (a)
Abstract