Modeling of transportation systems must invariably balance behavioral richness and computational tractability. In this paper, we develop a transportation equilibrium model and an algorithm for the simultaneous prediction of trip generation, trip distribution, modal split, and trip assignment on large-scale networks. The model achieves a practical compromise between behavioral and computational aspects of modeling the problem. It is formulated as an equivalent convex optimization problem, yet it is behaviorally richer than other models that can be cast as equivalent convex programs. Although the model is not as behaviorally rich as the most general equilibrium models, it has computational advantages. The applications reported in this paper of the model to real systems, i.e., the intercity transport network of Egypt and the urban transportation network of Austin, Texas, illustrate the computational attractiveness of the approach. These results indicate that equivalent optimization formulations are not as restrictive as previously thought, and hence, the equivalent convex programming approach for modeling and predicting equilibrium on transportation systems remains a viable and fruitful avenue for future consideration.
Between 1990 and 1997 intraregional trade was very low among the member countries of the United Nations Economic and Social Commission for Western Asia (ESCWA). Their export share fell from 10.9% to 8.6% of their total world exports, and their import share rose from 9.1% to 10.4% of their total world imports. Among the main reasons were complicated, costly, and time-consuming border controls and customs formalities. To overcome these obstacles and to promote greater economic integration among its members, ESCWA developed an integrated transport system in the Arab Mashreq (ITSAM). ITSAM comprises three basic components: an integrated (multimodal) transport network, an associated information system, and a methodological framework for issue analysis and policy formulation. The present research focuses on the development of an international freight simultaneous transportation equilibrium model (IFSTEM) to predict equilibrium freight flow patterns (times and costs) that can describe the behaviors of exporters and importers of different commodities over an international multimodal network covering ESCWA member countries. IFSTEM is considered a central component of the ITSAM methodological framework. The application of IFSTEM to the prototype shows that the model satisfies the behavioral aspects of the freight system, and its solution procedure is computationally tractable. This should encourage the full implementation of IFSTEM (after its calibration process) as a policy analysis tool and a decision-support system for transport policy makers in the region. The approach can easily be extended and applied to other regions of the world.
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