| Summary: | This paper develops a new combined network equilibrium model by using more behaviorally sound mathematical forms to represent the four travel choices (i.e., trip frequency, destination, mode, and route) in a conventional travel demand forecasting process. Trip frequency choice relates to the traveler decision on “making a trip” or “not making a trip” so it is given by a binary logit model. Destination choice is formulated as a parameterized dogit model of which the captivity parameters (expressed as functions of independent variables) allow individual travelers to be captive to specific destinations. Mode choice is given by a two-level nested logit model to avoid IIA restriction. Trip assignment is based on Wardrop's “user-optimized” principle. All model forms describing travel choices are in response to the level of services incurred by the transportation system. Through the introduction of inclusive values, the traveler decisions concerning trip frequency, destination, mode, and route choices are inherently interrelated and jointly determined.To obtain solutions of the new combined model, it was reformulated as an equivalent convex programming problem with linear constraints, a great advantage from the computational aspects. The model was applied empirically to a transportation network in New Jersey. The application results show that the new model is consistently better than the commonly used logit combined model in reproducing the observed trip flows from origin zones, origin to destination (O-D) trip flows, O-D trip flows by mode, and trip flows on the network links. Keywords: Combined model, Parameterized dogit model, Nested logit model, Wardrop's user equilibrium, Equivalent minimization problem
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