Demand-Supply Interaction in Assignment with Elastic Demand: Some Open Issues

This paper describes how models for traffic assignment to transportation networks simulate how supply and demand interact in transportation systems. These models allow the calculation of performance measures and user flows for each supply element (network arc), resulting from origin-destination demand flows, path choice behavior, and the reciprocal interactions between supply and demand. Assignment models play a central role in developing a complete model for a transportation system their results, in turn, are the inputs for the design and/or evaluation of transportation projects. In this paper a general fixed-point approach will be presented that allows dealing with multi-user multi-mode traffic assignment with elastic demand. The described approach is general enough to accommodate most existing demand models including those regarding path choice behavior, and can be applied to transportation systems with continuous and/or scheduled service. The adopted approach allows to easily defining conditions for solution existence and uniqueness, as well as algorithm convergence. Some issues still deserving research work will also be discussed.