Read the text below. Use the words given in Capitals at the end of each line to form a word that fits in the space in the same line. Railroads use signals and other means of controlling train . The chief purpose of traffic control is to prevent accidents and to make railroad faster, more efficient and . Most railroad signals consist of colored lights alongside or over the track. Each color has a meaning. Most railroads have adopted some form of the block signal system. The system is designed to keep a safe distance between trains on the same track. Most blocks range from 1 to 2 miles. Only one train is to be in a block at a time. Colored-light signals control to the block. No train may proceed from one block to the next without an all-clear signal. Automatic block systems are used on all tracks where trains travel at speeds of 60 mph and more and where freight trains move at speeds of 50 mph and over. The of automatic block signaling makes human errors practically . Besides, it is much and more reliable than the manual one. VARY MOVE OPERATE RELY DIFFER CHIEF TRAVEL ALLOW ENTER SIGNAL PASS APPLY POSSIBLE SAFE