Previous studies introduced a performance function for a toll link of which its level of service was an equivalent travel time (Chen et al. 2006, Chen and Subprasom 2007, Subprasom and Chen 2007). The link performance function used in the previous UE minimization algorithms represented link levels of service based on travel time and toll rates, but neglected the other important determinants of the user route choices such as vehicle operating cost (VOC) and the ride quality.