Abstract: This paper develops a method for estimating the link travel time by using the cell transmission model (CTM) and formulates a variational inequality problem of dynamic user optimal (DUO) based on the link variables. In our DUO formulation, the variables are towards the destinations, which, at each interval, can provide the link inflow rates, the link outflow rates, the link flows and actual travel times, consequently providing complete inducing information for travelers. To get the solutions, we employ a modified projection method for the problem based on link variables. Our DUO formulation is a good combination of the road traffic flow model and the network traffic assignment problem. Its practicability and advantages are confirmed by numerical simulation.