An optimal preview controller is designed for active trailer steering (ATS) systems to improve high-speed stability of articulated heavy vehicles (AHVs). AHVs' unstable motion modes, including jack-knifing and rollover, are the leading course of highway accidents. To prevent these unstable motion modes, the optimal controller, namely the compound lateral position deviation preview (CLPDP) controller, is proposed to control the steering of the front and rear axle wheels of the trailing unit of a truck/full-trailer combination. The corrective steering angle of the trailer front axle wheels is determined using the preview information of the lateral position deviation of the trajectory of the axle center from that of the truck front axle center. In turn, the steering angle of the trailer rear axle wheels is calculated considering the lateral position deviation of the trajectory of the axle center from that of the trailer front axle. To evaluate the vehicle performance measure, a driver model is introduced and it ‘derives’ the vehicle model based on well-defined testing specifications. The linear quadratic regular (LQR) technique is applied to the design of the proposed preview control scheme in the continuous time domain. The numerical simulation results show that compared with the baseline vehicle, the dynamic performance of the AHV with the ATS system is improved by decreasing rearward amplification ratio from the baseline value of 1.57 to 0.83 and reducing transient off-tracking by 80.6%.