This paper describes the estimation algorithm of the vehicle state and the road condition. This algorithm is formulated based on the Interacting Multiple Model (IMM) algorithm. Ten system modes of nonlinear tire are modeled according to the road friction. Changes of the ten system modes are also modeled as switching from one mode to another in a probabilistic manner. The mode probabilities and states of vehicle are estimated based on Extended Kalman Filter (EKF). This algorithm is evaluated in simulation study. Simulation results show that the algorithm is effective in the state estimation of vehicle and road surface.
