User fees based on vehicle miles traveled (VMT) are receiving much attention in policy debates as a means of financing the road infrastructure by eventually replacing the current funding model that uses fuel user fees. By focusing on partially modeling driver response to VMT user fees, this paper aims to investigate the potential traffic mobility effects of such fees from a traffic operational point of view under user equilibrium conditions. On the basis of a nonlinear optimization-based conceptual framework, the proposed traffic assignment model is evaluated by assuming heterogeneous values of time. A simple corridor with a single origin–destination pair is first used to demonstrate the sensitivity of network performance to the VMT user fees in a deterministic capacity environment. The effects of VMT user fees depend significantly on the characteristics of the underlying transportation network, such as the relative length of the alternative paths, the overall traffic demand level, and of course the mileage-based fee itself. An open-source mesoscopic simulator is used to assess the systemwide travel time effects of VMT user fees on a real-world network.