Block System
in railroad parlance, the division of a railroad into a certain number of telegraphic districts, the disthe amount of traffic, each block station having signaling instruments by which tance between which is determined by the signal man can communicate with the operator on each side of him. When a train enters any block a semaphore signal is lowered, and no train is allowed to follow until the one in front has reached the end of the block, when the signal is raised and at the same time lowered for the block ahead, etc. The block systems used in Europe and in the United States generally employ mechanical and electrical devices for lowering and raising the signal.