In this paper a new automatic approach to road extraction from aerial images is proposed. This method improves a recently introduced promising approach to probabilistic contour tracking, originally semi-automatic, by adding a fully automatic initialization strategy and a merging methodology, able to combine the different obtained results. The initialization strategy is based on the Hough transform and on some topological considerations, and the merging step is based on a new introduced quality measure, based on color and gradient information. Experimental results on real highly complex images show that the proposed approach is a promising and fully automatic method for extracting roads from images, even in presence of highly urbanized areas, occlusions or shadows.