In order to use ARCADY2, TRRL's program to estimate the performance of a particular roundabout layout, a traffic engineer must either produce a preliminary layout drawing and extract the required geometric input to the program, or make an educated guess at suitable parameters and, if they are satisfactory, attempt to fit a layout to them; in either case, there is likely to be a considerable amount of trial and error. This paper describes in some detail the research, conducted at Transport Studies Group, University College London, to perform this task wholly by a powerful microcomputer, with minimal user intervention. It describes the background to this research project, outlines current manual techniques for roundabout design, and surveys the design methods, optimisation procedures, and software developed. Two modes of operation are available: (1) automatic design, where the software designs the smallest roundabout able to handle the traffic demand well; (2) user intervention, which allows a traffic engineer to override the automatic design features and use the software as an 'intelligent' electronic drawing board coupled with a roundabout performance calculator. Finally, the paper describes the 'authors' programme for further research in this area: (1) development of an objective function, which is a composite measure of the costs of building and operating a roundabout; (2) the production of appropriate cost and performance models, representing the constraints defining feasible solutions.
Abstract