Temporal Expansion of a Transportation Network—I

A model is developed for determining the optimal timing of investment in the capacity of a transportation network for which there is a finite planning horizon. The model is long term and macroscopic in nature and is limited to single-mode transportation systems in which there is a unique path connecting each origin-destination pair. The form of the optimal solution for the special case of a two-link serial network is presented. Conditions, that may be checked in application, are developed that allow the optimal solution to be calculated by solving a sequence of independent, unconstrained optimization problems. If these conditions are met, the necessity for forecasting cost and demand data for the whole planning period is eliminated.