Modeling investment options for multimodal transportation networks

This research presents the development of a Multicommodity Multimodal Network Design (MCMND) model to be used as a planning tool when determining investment priorities for intercity freight networks. Such a model can be especially useful for the case of regions in developing countries that have experienced considerable growth and, consequently, have demanded high service levels in certain areas and corridors that did not have an adequate transportation infrastructure. The MCMND model is designed to select the best set of investment options for a multimodal regional network, given a limited investment budget. The main component of the model comprises the solution of a nonlinear bilevel multimodal network design problem formulated to choose investments so as to minimize the transportation costs incurred by users (shippers) and the environmental impacts caused by the use of less efficient modes of transportation in moving freight. Investment options to be considered by the model may involve the addition of new physical links to the network, the improvement of existing links (i.e., increase in capacity), and the location of intermodal transfer facilities at specified nodes of the network. The representation of the multimodal network is performed at a level of detail appropriate for strategic planning for a large region. The demand for transportation services is fixed and exogenous to the model. Mode choice in shipping freight is modeled in combination with traffic flow assignment, with the assumption that goods are shipped at minimum total generalized costs. Travel costs (shipping cost and delay) are considered to be dependent on link flows, according to an exponential delay function. A path-based stochastic user equilibrium assignment algorithm is used to distribute trips over the multimodal network according to a logit-type model. The proposed solution algorithm consists of a heuristic procedure based on a column generating technique, which allows the solution of large scale problems in a reasonable time. The multimodal network design problem is called the master problem, with its subproblem being defined as a bi-criteria path finding problem. This solution procedure was tested for a small network and it was found to approximate the optimal solution to that test problem in a satisfactory way. The Tiete-Parana Valley, located in the Southeast region of Brazil, was used in the development of a pilot application of the MCMND model to assess its applicability and its efficiency when dealing with large networks. This pilot application also served to emphasize the importance of an interface between the MCMND model and a Geographic Information System (GIS) in solving real-life problems.