Rear-end collisions occur at higher frequency in Japan. The causes of rear-end collisions were therefore investigated. Accident statistics were used to conduct a statistical traffic accident analysis. Simulation was then used to perform an accident analysis on the basis of those studies. The results suggested that many of these accidents were caused by momentary inattention during daily driving. Research was therefore carried out to determine what kind of collision avoidance assist system would be effective for use at such times. The researched system used warning and brake control. The warning timing was set so that it would not interfere with the driver nor lose its impact as a warning. The result was creation of a system capable of contributing to the reduction of rear-end collisions.