Road restoration projects primarily retain the existing road alignment and improve the cross-section and riding quality. This is in spite of the fact that the alignment may contain elements (particularly crests) that do not conform to the design criteria in current design guides. For low volume roads it has long been recognised that they do not have to be designed to the same standard as high-volume roads or the more important roads in the road network. Yet some key design criteria such as vertical and horizontal curvature are not dependent upon traffic volume. So alignment design is usually reduced to "what fits" because of cost. Consequently, many practitioners now consider that both types of project involve minimal geometric design effort and this seems to have contributed to a general decline in the understanding of the importance of geometric design for all roads. This paper examines the need for more appropriate geometric design criteria and practices for road restoration projects and new low volume roads. It describes the Extended Design Domain concept that has been developed by the Queensland Department of Main Roads for restoration projects and how some of its design values may be applied to new low volume roads. (a) For the covering entry of this conference, please see ITRD abstract no. E217099.
Abstract