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This paper investigates the use of four-wheel steering system (4WS) for the automatic vehicle control in the context of path tracking. The 4WS vehicle is assumed to be set up in a previously studied look-down reference system with sensors installed on the vehicle's front and rear bumpers to measure its lateral displacements from the reference path. Past research in the path tracking control have showed the difficulties to design a controller that is robust against the intensive vehicle modeling uncertainties and disturbances. In this paper, noticed the new dynamic characteristics of 4WS vehicles, we firstly found a new robust sliding mode controller for a class of linear systems and then apply it to the path tracking problem of 4WS vehicles. Both theoretical analysis and simulations show that with the proposed controller, the system's tracking accuracy, stability and robustness against the parameter variances and external disturbances, especially the changes of road friction condition, longitudinal velocity and crosswind forces, are identically guaranteed.