Junction design in Britain is assessed principally in terms of criteria relating to junction capacity, total junction delay, and safety. This paper outlines a strategy for optimising geometric design that includes automatic optimisation of a quantifiable measure of junction performance, namely capacity, within an interactive program. In Britain, the capacity of a traffic stream at a priority junction can be determined by relationships developed at the Transport and Road Research Laboratory. These relationships can be used to form a set of capacity constraints which allow linear programming techniques to be used to assess the capacity of the priority junction for any given geometry. By the addition to the capacity constraints of other design constraints such as those of safety and cost, a problem of maximising the junction capacity can be completely specified. However, geometric constraints become non-linear, making the optimisation procedure complex. Also, there are a number of discrete choices involved in the design of any junction such as number and location of islands and obstructions to visibility; this further complicates the automatic optimisation process. The interactive procedure outlined in this paper involves producing an initial design for each discrete choice of layout, assessing capacity and adapting those features that have the greatest effect on capacity. The adaptation of geometry can be done automatically, incorporating rules representing good, safe design, or interactively by the engineer working from a graphical representation of the junction.
Samenvatting