Abstract: In a transportation network with users classified into two categories, the first category chooses the route according to user equilibrium(UE)  principle and the second category chooses the route according to Logit-based stochastic user  equilibrium(LSUE)  principle. In this paper, a variational inequality is proposed to  formulate the mixed equilibrium travel behavior associated with user equilibrium and Logit-based stochastic user  equilibrium. Likewise, the upper bound of efficiency loss for the  mixed equilibrium is described as a general formula. It is shown that the upper bound is related to the  topological structure of networks, transportation demand and the demand  ratio.