This paper proposes an automated steering control system for passenger cars. The control strategy used is a look-down reference system which uses a sensor at the front bumper to measure the lateral displacement and a GPS to measure the heading orientation. Firstly, the road curvature estimator is designed based on the steering angle. Secondly, the steering angles can be estimated by using the sensor and the GPS information. The estimation algorithm employed is an observer for a new extended system model, in which the steering angle and its derivative are viewed as two state variables. Then, the lateral displacements estimation and the control algorithm are investigated. An accurate and real-time estimation of the lateral displacements with respect to the road can be accomplished in such a control system. The closed loop controller is used as a compensator to control the lateral dynamics of the vehicle. The vehicle dynamic and control system are simulated with Matlab Simulink. The proposed estimation and control algorithms are validated by simulation results. The results show that the system provides a good and robust performance for vehicle to follow or track a reference path.