Shape Grammars for Intersection Type Choice in Road Network Generation

Abstract

Urban systems continue to grow worldwide due to population growth and migration. Therefore, urban design guidelines are strongly needed for planning purposes. However, current network and urban design guidelines lack of a fundamental research bases regarding design recommenda- tion. Shape grammars describe in the form of rules how network elements and land used types are added to each other. Shape grammars have the advantage of their ease of application in urban and interactive planning, their comprehensiveness, and their low computational requirements. Previous work showed the impact of hierarchical shape grammar rules for road networks. It could be shown a significant impact on hierarchical road type implementation. This paper especially sheds light on various intersection types and the corresponding expected delays for the road users. It is quantitatively shown that intersection delays mostly depend on their number of arms and the current through traffic shares. Propositions for shape grammars and future standards are made regarding intersection type alignment. The proposed alignments are evaluated in virtual networks, generated on featureless planes. The generation of virtual network layouts respects the shape grammars in consideration. The virtual networks are compared regarding the corresponding shape grammars. The results show the high performance of roundabouts for variable demand. The proposed Matrix shape grammar slightly reduce network performance compared to the most optimal intersection alignment in exchange for a simple shape grammar rule. Future research is proposed, including additional shape grammars for land use interactions, and growth processes.