In this paper, a road detection method based on an image segmentation algorithm is presented. Road detection process is a key issue for an autonomous driving system in urban environment. Image-based road detection algorithm is applied on sources of visual information recorded by cameras when our car is running on road. Our method combines a posteriori probability and visual information for image segmentation. The method is composed of two steps. Firstly, a road identifier is trained with supervised learning algorithm. Secondly, road regions are detected by combining a posteriori probability and visual information using image segmentation algorithm. Experimental results are presented for road images in actual driving video acquired in urban areas.