In the present work, an active steering assistance system for heavy vehicles is developed to prevent lane departure and let the vehicle follow the road's centre line. The controller is based on the super-twisting algorithm. An estimator based on the sliding mode observer is also developed to estimate the vehicle dynamics. The lateral positions and speeds are then controlled to keep the vehicle in the centre of the lane. The lateral offset and the relative yaw angle are supposed to be measured and the road curvature to be known. Some simulation results are given to show the quality of this steering assistance system. Copyright © 2011 John Wiley & Sons, Ltd.