A safety vehicle using an obstacle detection system with a stereo image sensor has been developed. The stereo image sensor was chosen as a more suitable sensor, compared to a laser radar or a millimeter wave radar. The matching method adopted for this stereo system is the small area based matching to yield a distance distribution image. The road shape and solids are recognized from the distance distribution image. This safety vehicle has three functions for the ''avoidance stage'' proposed in ASV (Advanced Safety Vehicle) project as follows: (1)a collision alarm system. (2)an autonomous collision avoidance system. (3)lane keeping alarm system. Reduction rates by this safety vehicle for a rear-end collision and a collision encountered at a intersection were estimated. It was recognized that the system was greatly effective for both type of collisions.