of electricity, the capacity of the elevated lines in car-miles per day was increased 331⁄3 per cent, and this in spite of the facts that the subway system had inaugurated during this time a service furnishing over 75 per cent, that of the steam elevated and that the surface lines showed little or no decrease. During the two years ending 1906 the increase in passengers on all the lines of New York city numbered more than 114,000,000, which is about 75 per cent, of the ultimate capacity of the subway system. In order to handle this continuously increasing demand it has now become necessary to consider the construction of additional subways.
Returning to the second of the reasons given for changing to electricity, the general statement that it will pay to electrify a steam railroad may not be made without important qualifications. It is admittedly true for the majority of steam roads of any considerable size and density of traffic that the operating expense would be substantially reduced by electric operation. Figures showing that this saving, together with the returns from increased business, is sufficient to offset the interest charges on the necessary capital are still few. Such figures have, nevertheless, been given for existing roads on which the transfer to electricity has been made. On the other hand, on railroads operating light trains and comparatively infrequent traffic, it is at once evident that there would be little if any saving in operating expense in changing the motive power. Much of the economy possible under electric operation results from the combination of all the locomotive boilers and engines into a central power plant. It is obvious that when the number of such locomotives is small that the cost of the power plant and the motor equipments may far outweigh the economies obtained. There is, however, an intermediate class of road, many instances of which have been equipped electrically, in which the saving in operating expense, together with the usual increase of business following the electric installation, are looked to for a reasonable return on the capital invested. The enormous amount of capital represented by the steam equipments of existing railroads, which can not be applied to the new equipment, is the most serious obstacle to the general adoption of electricity as motive power. It will only pay to electrify in those cases where the economies in operation and the increase in business will outweigh the charges on the new capital necessary.
The public will invariably drift to an electric rather than a steam route between given points. Moreover, when a steam road is paralleled by electric service, not only does the latter take the bulk of the traffic, but the traffic itself increases in volume. Further, when a sparsely settled section is penetrated by an electric road, population and consequent business follow promptly. These facts are now matters of common observation. One extreme example will indicate the lengths to