The ideal train schedules, or those by which the systems are regularly governed, are charted out beforehand on a ruled sheet, as a ship’s course is charted on a voyage, in the main office of the railroad.  Each engineer and conductor is provided with a printed copy in the form of a table giving the time of departure and arrival at the different points.  When the trains run on time it is all very simple, and the work of the despatcher, the man who keeps track of the trains, is easy.  When, however, the system is disarranged by the failure of a train to keep to its schedule, the despatcher’s work becomes most difficult.  From long training the despatchers become perfectly familiar with every detail of the sections of road under their control, the position of every switch, each station, all curves, bridges, grades, and crossings.  When a train is delayed and the system spoiled, it is the despatcher’s duty to make up another one on the spot, and arrange by telegrams, which are repeated for fear of mistakes, for the holding of this train and the movement of others until the tangle is straightened out.  This problem is particularly difficult when a road has but one track and trains moving in both directions have to run on the same pair of rails.  It is on roads of this sort that most of the accidents occur.  Almost if not quite all depends on the clear-headedness and quick-witted grasp of the despatchers and strict obedience to orders by the trainmen.  To remove as much chance of error as possible, safety signalling methods have been devised to warn the engineer of danger ahead.  Many modern railroads are divided into short sections or “blocks,” each of which is presided over by a signal-tower.  At the beginning of each block stand poles with projecting arms that are connected with the signal-tower by wires running over pulleys.  There are generally two to each track in each block, and when both are slanting downward the engineer of the approaching locomotive knows that the block he is about to enter is clear and also that the rails of the section before that is clear as well.  The lower arm, or “semaphore,” stands for the second block, and if it is horizontal the engineer knows that he must proceed cautiously because the second section already has a train in it; if the upper arm is straight the “runner” knows that a train or obstruction of some sort makes it unsafe to enter the first block, and if he obeys the strict rules he must stay where he is until the arm is lowered At night, red, white, and green lights serve instead of the arms:  white, safety; green, caution; and red, danger.  Accidents have sometimes occurred because the engineers were colour-blind and red and green looked alike to them.  Most roads nowadays test all their engineers for this defect in vision.

In spite of all precautions, it sometimes happens that the block-signals are not set properly, and to avoid danger of rear-end collisions, conductors and brakemen are instructed (when, for any reason, their train stops where it is not so scheduled) to go back with lanterns at night, or flags by day, and be ready to warn any following train.  If for any reason a train is delayed and has to move ahead slowly, torpedoes are placed on the track which are exploded by the engine that comes after and warn its engineer to proceed cautiously.