A Graphical Explanation of the two Principles and two Techniques of Traffic Assignment

Abstract

The purpose of the paper is to identify issues related to the two fundamental principles of traffic assignment and two techniques used for its solution. Firstly, the inter-relationships among the average, marginal total and integral forms of the travel time (cost)-flow function are discussed. The choice of the appropriate form of the travel time (cost)-flow function depends on the assignment technique (heuristic loading or mathematical optimisation) and the assignment principle (user-optimising or system-optimising) adopted for use. A table is given as an aid for this choice. A graphical explanation is then presented, based on the fundamental two-route single-demand assignment problem to illustrate the usefulness of the graphical approach for simple analysis of various issues related to traffic assignment.