Block System

a method of preventing collisions on railways. According to this plan a line of railway is divided into sections guarded at each end by signal towers or semaphores operated by local officials in constant communication by telegraph. No train is allowed to enter a section until the display of a wooden arm on the signal tower indicates that the section is clear. In this manner no two trains are permitted to be on the same section of track. If signals are displayed properly and obeyed, collisions are impossible. See Railroad