In automatic lateral control, which will play a key role in highway automation, vehicles must follow a given path and vehicle direction must be controlled as desired. Therefore, the ideal is for the lateral motion and yaw motion of the vehicle to be controlled independently. This requires at least one additional control input which is independent of the front steering angle. This paper explores the use of two independent control inputs, which are the front steering angle and an extra control input. Three types of extra control inputs are considered: (1) a differential driving torque between the two front wheels; (2) that between the two rear wheels; and (3) the rear steering angle. The analysis utilizing a linearized vehicle model shows that the front and rear independent steering allows a wider variation of lateral velocity and yaw rate in the steady state. A control algorithm with front and rear independent steering, which features continuously changing gains dependent on vehicle velocity and road conditions, is presented. Performance evaluation is based on a simulation study on a nonlinear vehicle model and an experimental study with a laboratory model vehicle.

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