Steering control for passenger cars on automated highways is analyzed. The feasibility of an automatic steering system based on absolute positioning global positioning system (GPS) and a magnetic marker guidance system has been evaluated using computer simulations. State estimation and control algorithm issues are examined for such a control system. By use of GPS and a magnetic marker sensor, an accurate and real-time estimation of the vehicle's lateral displacements with respect to the road can be accomplished. A steering control algorithm based on road curvature preview for achieving good road tracking and providing ride comfort is also presented. The proposed estimation and control system are validated by simulation results.