This study aims to reduce the severity of injuries caused by and the frequency of rear-end vehicle collisions. A better collision prediction method is proposed by means of millimeter-wave radar sensors able to rapidly detect potential collisions and alert drivers. Implementation of the system would bring about a reduction in accidents and potentially reduce the severity of the accidents that cannot be avoided. The proposed collision avoidance system adopted millimeter-wave radar sensors to collect information on vehicle’s rear surroundings. The designed experimental device has several unique features. The device has a wide monitoring range, incorporates a continuous detection process, and contains a rapid warning system. A series of real-world experiments were performed on cars (Model: Tercel 1.5, Toyota) to demonstrate the monitoring efficiency and warning frequency of this device under several operating conditions. This study furthered the development of a safe technology for avoidance of rear-end collisions, and this offers a novel system which can be used in a variety of vehicles to reduce the frequency of rear-end vehicle collisions.