Weighted Digraph Models for the Assessment of Energy Use and Air Pollution in Transportation Systems

This paper describes extensions, to weighted and double-weighted digraphs, of the author's earlier work on building and analyzing energy-demand signed digraphs. Several weighted and double-weighted digraphs are built to provide a test of the construction methodology, to provide a test of the methods of analysis of such digraphs, and to illustrate the type of analysis one can make using such digraphs as models of complex systems. The digraphs are constructed within the context of the transportation system of a hypothetical metropolitan area, similar to the County of San Diego, California. The digraphs are used to compare fuel consumption and air pollution under two scenarios: the nominal case, where clean air standards are met by some retrofitting of cars with smog control devices; and the bus case, where cars are banned and an expensive wide-ranging bus system is introduced. It is concluded that weighted and double-weighted digraphs can be constructed relatively inexpensively and that at least weighted, and probably double-weighted, digraphs can be used at an early stage of a policy-making task to set directions for further research.