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118 Interpretation of Railroad Signals
Interpretation of Railroad Signals
Railroad signals regulate train traffic, just as road signals regulate road traffic. In fact, road traffic signals were developed from railroad signals.
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Each section of track, between signal lights is called a “block.” Blocks are three to six miles long. Generally, only one train is allowed at one time in each block. The signals regulate whether or not a train is allowed to enter a block, and at what speed.
Trains are heavy and therefore take more distance to stop than automotive. Trains require one-half to one-and-a-half- miles to stop. The engineers need plenty of warning to stop the trains. Part of this warning is achieved by positioning yellow lights ahead of red lights (unlike on roads, where the yellow lights are housed in the same traffic control devices).
Green Signal—A green signal means that at least the next two blocks are clear.
Yellow Signal—A yellow signal indicates that the next block is clear, but that the block following that is occupied or otherwise unsafe to enter. Thus the next signal - located farther ahead of the train - is red, and the train has one block to stop.
Red Signal—A red signal can mean that: (1). The next block is occupied (2). A train traffic controller may want to hold the train at that location, to allow another train to pass or (3). Some other danger situation exists, such as a switch being improperly set in the tracks ahead.