The vehicle lateral control system performs lane keeping and lane changing tasks on the automated highways. It is of critical importance for the lateral controller to be robust with respect to model uncertainties and various road conditions under the constraints of limited actuator power. In this paper we proposed a controller design method which consists of two steps: (i) designing a state-feedback controller of an "augmented plant" by assuming all state variables are available and (ii) converting it to an output-feedback controller. The state-feedback controller in step (i) is designed to achieve all the control objectives under the assumption that state feedback is feasible. The conversion to an output-feedback controller in the second step preserves the closed-loop characteristics; hence both state-feedback and output-feedback controllers have the same performance and robustness. Experiments on a passenger car show that small tracking errors and smooth steering command can be achieved by the proposed controller.