Abstract: A device for preventing collision of trains includes two units, a stationary signal sending unit mounted on the wayside and a moving control unit mounted on the locomotive. The signal sending unit including the traffic light system transmits a D. C. voltage, zero, positive, or negative value, representing red, yellow, or green traffic light, to the control unit through two contacts, one mounted on the wayside and one mounted on the locomotive. The control unit includes an electro-responsive valve, the air brake system of the train, and four speed-switches. The electro-responsive valve is connected by a pipe to the air brake system of the train. Openings of the electro-responsive valve will cause brake applications. The so organized device will cause the train to stop if the train runs through a red traffic light, and will cause the train to restrict its run under a pre-set low speed limit after passing the red traffic light.