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Automation to a very high degree makes the best possible economic sense in an operation that is dedicated to a single high-volume task. Typical of this type of operation is the handling of coal in bulk, and fully automated systems associated with this task include the Norfolk & Western Railroad’s traffic to Lamberts Point and the Chesapeake & Ohio Railroad’s nearby system, delivering coal to Newport News. The Norfolk & Western Railroad’s coal is classified into almost 1,000 different categories, and the blend specified by a particular customer is produced by an automated system, which ensures the speed and ratio of coal falling from bins onto conveyor belts to yield exactly the desired combination of sizes or grades. The right blend and quantity of coal is then transported out to the relevant ship by huge loading towers with 120-ft (36.6-m) extendable booms that drop the coal in the ship’s hold.
In the normal classification yards, where there is a mixture in the types of freight handled, there are wider-ranging systems such as the automatic weighing of cars as they pass over the hump; moreover, more capable computerized systems allow the establishment not only of the total weight but also the loading on each axle, the latter allowing unbalanced loads to be redistributed so that they cause no problems in high-speed mining. As noted above, one of the aspects of freight that offers the railroad operator the optimum conditions for a useful profit is the operation of unit trains, in which all the cars are bound for the same destination. It was for the optimization of this process that the Atchison, Topeka & Santa Fe Railroad constructed its huge classification yard at Barstow in California. Here, traffic previously assembled at yards in other parts of California is brought together, before being hauled to the east. The effective use of the yard’s facilities allows the concentration, in time and space, of cars that can then be classified by destination and shunted accordingly to allow more timely assembly of trains. A similar but not so capable yard is located at Kansas City for the classification of westbound freight, but intermediate traffic is hauled to Barstow in mixed freights and then made up into trains for the various destination points in California. Once a train had left the yard, there must be continued control of its movement for two primary reasons; the arrival of the train at its destination at the right time, and the control of all the movements to a given area to ensure that there are no collisions. The first effective way in which this task was accomplished in the 19th century, was by means of the newly created telegraph system to issue train orders. Linked by telegraph to station operators, the central dispatcher sent orders governing the movements of all the trains on the line, and these orders were then written out and passed to the engineer and conductor of every applicable train. This system ensured that each engineer was given his instructions, told of all other traffic on the line, informed of the priority accorded to the various trains, and all other relevant details. The system still exists in some parts, and is of particular importance when any train must progress along a long stretch of single-track line with passing sections that trains moving in opposite directions must reach at the same time: thus the engineer might be instructed to move to a specified passing point, with a loop in the track allowing him to pull off the main line and wait until the other train has passed before continuing. The engineer of the other train would have been told to move off but also warned of the first train and told where to expect to find it waiting in its loop. If the sidelined train was not in its appointed place, the train with the right of way would stop and telegraph the dispatcher by means of a portable telegraph machine that could be tapped into the line at the side of the track. So important was the telegraph to successful and safe operation of the railroads that it was one of the fundamental rules that no train should depart without a telegrapher.
Improvement with the passage of time led to the introduction of block signaling for sections of any line where there was heavy traffic. This allowed the control of all the trains on that section by means of semaphore or colored light signals. These were operated from a central control point with the levers for setting the switches, and was later enhanced by an interlock arrangement between signals and switches mechanically connecting all the controls, the arrangement ensured that a signal could not be set unless the individual switches were in the appropriate position for the instruction given. Block signaling is impractical for many parts of a large railroad network, and here the modern system is centralized train control. This was developed during the 1920s, and places the whole section of line under the dispatcher’s direct control, with points and signals set by electrically actuated control. The lag in time inherent in the transmission and execution of the command signals is then reduced by the replacement of the original electro mechanical controls by electronic systems, and the dispatcher’s control panels have also been enhanced so that a continuous indication of any train’s movement is represented by colored lights. Radio equipment in the engineer’s cab provides an additional means of control from and communication with the control center, and the cab has also been fitted with a signaling system to provide a continuous picture of the line yet to be covered, this replacing the older system that provided only limited indications from intermittent trackside signals. |