Browsing by Author "Fernandez, JE"

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    A multi-modal supply-demand equilibrium model for predicting intercity freight flows
    (PERGAMON-ELSEVIER SCIENCE LTD, 2003) Fernandez, JE; de Cea, J; Soto, A
    In this paper a new approach to intercity freight transportation system modeling is developed. Modeling formulation considers supply-demand equilibrium, where the demand side represents the behavior of shippers (cargo owners) and the supply side represents the behavior of carriers (transportation operators). Shippers decisions considered include choice of destination, mode, carrier for pure modes and transfer point for combined modes. Carriers take routing decisions over a multi-modal, multi-product and multi-operator network. A new mathematical formulation, not known before, is proposed to find consistent equilibrium solutions for modal O-D shipments, network flows and levels of service. Necessary conditions are deduced to show that the solutions obtained, from the mathematical formulations proposed, satisfy the behavioral principles assumed in each case. It is shown that special rationality conditions are required, with respect to fares charged and network routing decisions, to obtain consistent supply-demand equilibrium solutions. Sufficient conditions for the existence and uniqueness of solutions to diagonalized versions of the mathematical problem formulated are deduced. Finally, a general solution approach is proposed and an application example is developed to illustrate the characteristics of the model and solution algorithm. (C) 2003 Elsevier Science Ltd. All rights reserved.
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    A strategic model of freight operations for rail transportation systems
    (TAYLOR & FRANCIS LTD, 2004) Fernandez, JE; De Cea, J; Giesen, R
    This paper formulates and analyzes a new strategic model for freight rail transportation systems. The objective of the model is predicting equilibrium flows and levels of service, given origin-destination (O-D) transportation demands for a set of different products. The model has the following distinctive characteristics: (1) a detailed representation of different freight rail yard operations is made and railway services with their operational characteristics are considered explicitly; (2) priorities are assigned to different types of freight cars to be moved, depending on the products transported; (3) the distribution of empty freight cars and their assignment over the rail network is treated simultaneously with the assignment of products to be transported; and (4) capacity constraints are considered for the movement of various products. Solution approaches are discussed. The model can be used to evaluate freight railway systems, including yard operations and rail services management policies.
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    Production costs, congestion, scope and scale economies in urban bus transportation corridors
    (PERGAMON-ELSEVIER SCIENCE LTD, 2005) Fernandez, JE; de Cea, CJ; de Grange, L
    A microeconomic model is developed to study the main characteristics of production costs in urban bus corridors. A multiproduct formulation is used, considering trips during peak and off peak periods as different products. The influence of the demand structure and congestion in the production of trips are considered in the analysis. Production and cost functions are specified using a fix proportion technology. The characteristics of period specific economics of scale, ray scale economies and transray convexity are studied with and without congestion. A numerical example is presented to illustrate the results obtained. (c) 2004 Elsevier Ltd. All rights reserved.
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    Solving network equilibrium problems on multimodal urban transportation networks with multiple user classes
    (TAYLOR & FRANCIS LTD, 2005) de Cea, J; Fernandez, JE; Dekock, V; Soto, A
    A modelling approach for solving quite general network equilibrium problems ( with fixed trip productions and attractions) intrinsic to the urban transport planning process is presented. The framework can consider a variety of demand models and route choice behaviours within the same implementation, including multiple user classes and combined travel modes that interact on the same physical network. The demand choices are assumed to have a hierarchical structure. When trip distribution is variable, a doubly constrained entropy-maximizing model is considered at the first level of choice and a hierarchical logit model is used for the remaining demand choices ( time of departure, travel mode, transfer point for combined modes, etc.). If trip distribution is considered to be exogenous, the demand choices are modelled as a hierarchical logit. One of the main features of the model is that it considers the effects of congestion on the road network as well as congestion and capacity constraints effects in each public transport service network. The problem is formulated mathematically as a variational inequality, with asymmetric cost functions, and solved following the diagonalization procedure. Each iteration of the aforementioned procedure solves an optimization problem using the Evans algorithm. Sufficient conditions for the existence and uniqueness of the solution to the diagonalized problem are obtained. The main results of a simple example ( solved with an academic version of the proposed algorithm) are presented to show the consistency of the equilibrium flows and levels of services obtained using the model. Finally, a real scale implementation of the model is briefly described to show the feasibility of its application.