Network Equilibrium Model with Dogit and Nested Logit Structures

This paper develops a combined equilibrium model for the simultaneous prediction of trip distribution, mode choice, and trip assignment. Trip distribution is formulated as a dogit model to take into account travel behavior of compulsory (work) and discretionary (nonwork) trips. Mode choice is given by a two-level nested logit model to avoid the independence from irrelevant alternatives restriction. Trip assignment is based on Wardrop's user-equilibrium principle. The log sums of the mode choice model were computed and fed back into the trip distribution step. Under this iterative process, destination choice of discretionary trips would respond to changing travel cost conditions occurring in mode choice and trip assignment steps, whereas destination choice of compulsory trips would remain fixed in the study time period. The proposed combined trip distribution, mode choice, and trip assignment (CDMA) model was reformulated as an equivalent convex programming problem with linear constraints and applied empirically to a county-level network in New Jersey. The results indicate that the CDMA model is better than the commonly used logit combined model in reproducing the observed link flows, origin–destination (O-D) trip flows, and O-D trip flows by mode.