Comparison of hierarchical network design shape grammars for roads and intersections

Abstract

Urban systems are growing fast in many countries today and depend essentially on ecient transport networks. Significant productivity gains in urban systems can be achieved by improving transport infrastructure and thus reducing overall costs of travel. Shape grammars provide a solid foundation for coherent transport network design, and concurrently reduce complexity of planning processes. Shape grammars describe how network elements are joined with each other. However, only a few are listed in standards for network design without any fundamental research basis. Therefore, shape grammars remain vague and the standards lack of clear recommendations. In this paper, shape grammars for hierarchical network design are examined for di erent transport networks. The investigated shape grammars include di erent link and intersection types. The network models are artificially created to avoid a bias in the results due to history. The networks are optimized regarding an infrastructure and user cost function. Shape grammars significantly a ect transport network performance. As expected, the distribution of link types a ects the network eciency. However, intersection types and the corresponding delays in travel time have a remarkable and even larger e ect on network performance. In the future, more shape grammars will be examined to shed light on the impacts of relevant grammars for transport network design and to derive clear recommendations for urban planners.