Abstract
This paper examines a model due to Nguyen for estimating origin-destination (O-D) trip matrices from observed traffic flows on each network link. It is shown that the bilevel optimization methods for choosing an 0-D matrix can be transformed into single convex programs. Under the condition that the set of observed link flows is an equilibrium flow pattern, Nguyen's model is shown to be equivalent to an underspecified system of linear equations with non-negative variables. By exploiting the properties of the feasible region of the system, more simple method such as least squares technique can be used to obtain an 0-D matrix which, when user-optimally assigned to the network, reproduces the observed link flows exactly.
