Page:Popular Science Monthly Volume 74.djvu/218

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and by the schedule speed. Speaking generally, longer trains and hence fewer trains on the line at one time, are to be had only at great sacrifice of speed. The longest freight trains weigh from 2,000 to 3,000 tons and are only operable on level track. On reaching mountain grades, such trains have to be broken into two or three parts, which, therefore, on single-track roads increase the number of passing points and subsequent delays, thus rapidly shortening the headway between trains and filling the line to its capacity. Schedule speeds on such grades now average about ten miles per hour. The operation of two or more locomotives in a train is not satisfactory, owing to the impossibility of securing simultaneous cooperation of the several motive units. As already stated the tractive effort at high speeds is much greater for the motor than for the steam locomotive; hence, in the case of electric operation, the limiting weight of the train on grade is higher, also the schedule speed may be largely increased by the use of double or triple headers. This method of operation is perfectly possible under electricity by the system of multiple control, already mentioned, and the length of a train is limited only by the strength of the draft gear. This limit would disappear if all freight cars could be equipped with a simple standard cable, enabling the placing of an electric locomotive in the middle or at the end of a train. This cable would be necessary to secure the simultaneous operation of the several locomotives.

A few comparative figures bearing out the above facts of the possible methods of increasing railway business are not without interest. A typical western freight locomotive, weighing with its tender 165 tons, can develop continuously a draw-bar pull of 25,600 pounds, up to a speed of 15 miles per hour. An electric locomotive, weighing 100 tons, can develop this value of pull, up to a speed of 37 miles per hour. Another similar type of electric locomotive gives 56,800 pounds, up to 23 miles per hour, and still another 8-motor type can develop 113,600 pounds draw-bar pull up to a speed of 23 miles per hour.

A late type of Mallet compound locomotive, weighing 300 tons, can develop continuously 2,180 horse power at its driving wheels. A New York Central electric locomotive can do the same and weighs only one third as much. The cost of each locomotive is about the same. It may be noted that 200 ton-miles are saved in every locomotive mile if the electric locomotive is used instead of the steam locomotive. At 40 cents per locomotive mile and 100 miles per day the saving is $40 per day or about $15,000 per year. The saving on this account alone would in two years pay for the electric locomotive. Another type of Mallet locomotive, weighing with its tender 250 tons, can haul a train weighing 330 tons up a 2.2 per cent, grade at 15 miles per hour. A 100-ton electric locomotive can haul a train of 800 tons under the same conditions. The total train weights are thus 580 and 900 tons and the