Simultaneous estimation of the origin–destination matrices and the parameters of a nested logit model in a combined network equilibrium model

This paper deals with the inverse problem of a type of traffic equilibrium models with combined modes. This problem consists of obtaining a parametrization of the equilibrium model from a set of observations of the outputs for the model. The inputs for the model are an origin–destination (O–D) trip matrix for the various alternatives that have been considered, and a set of parameters for a nested logit model used as a demand model. This model has been formulated by using a new approach called the calibration and demand adjustment model (CDAM) based on bilevel programming which simultaneously estimates an O–D matrix and the parameters for the nested logit model. In this paper, the CDAM properties are studied and it is proved the CDAM solution exists. This paper develops a heuristic column (paths/hyperpaths) generation algorithm for the CDAM. This algorithm iterates between the network equilibrium problem and that which is used to obtain a set of paths when equilibrium is attained, and the CDAM is restricted to the set of previously generated columns (the so-called restricted CDAM). The restricted CDAM is formulated as a single level model under certain hypotheses and it furnishes a solution upon which to base a new estimation of the O–D matrix and the vector of parameters. The computational tests on the algorithm have been carried out using data from a multi-modal network in Madrid.