The current as produced is, according to the most approved practice, of the three-phase alter nating type, and at a pressure of from 6,000 to 11,000 volts. This current, in appropriate sub stations, is transformed and converted into di rect current at a pressure of about 550 volts, and as such is fed to the line. The means of delivering the current to the trains is usually by means of a third rail set on the floor of the subway, and at a distance of about two feet from one of the track rails. From this rail the current is taken by contact shoes on the motor cars and led to the motors themselves. On some railroads the trains are drawn by electric locomotives at the head of the train, coupled in the same manner as steam locomotives. The most desirable practice, however, is to distribute the power to various cars in the train, so that the weight of the cars and passengers furnishes the necessary track cohesion. This method of working is called the multiple unit system. The various motors thus distributed through the train are controlled from either end of the train or can be arranged so as to be controlled at any intermediate point. In the New York subway the most powerfully equipped cars as yet con structed are in operation. The motor cars have each two 200 horse-power motors, and are adapted so that the express trains can be corn posed of five to seven motors and three trailers. The total weight of an eight-car train, including passengers, standing space occupied as well as seats, is about 300 tons. The nominal power capacity is, therefore, six and two-thirds horse power per ton of train, or, say 10 horse power per ton of train available during the short period of acceleration. This power capacity is greatly in excess of European or other American prac tice on account of higher speed to be realized. Inasmuch as subways are built to convey large numbers of passengers, it becomes necessary that the cars be run in trains and not in single units, except in the case of Boston, where the subway was built for the passage of the surface trolley cars. The trains vary in .length from 2 to 10 cars.
The various subways in Lon don, as well as in Glasgow, Berlin and Buda pest, are the property of private corporations. In England the authorization for such com panies has to be procured by a special bill passed through Parliament, the ownership of the work being vested in perpetuity in the cor poration, the various powers of the corporation being expressed in the act.
New York, Boston and Paris adopted the principle of municipal ownership, but under dif ferent methods of application. In New York the Dual System was created when the city through the Public Service Commission, on 19 March 1913, entered into an agreement with the Interborough Rapid Transit Company and the New York Municipal Railway Corporation (the latter a subsidiary of the Brooklyn Rapid Transit), providing for the construction and operation of new subway lines, elevated and subway extensions, of existing subways, and third tracking and extensions of elevated lines. The city and the two companies contributed large sums for the construction of subway lines, while cost of equipment, plus the cost of construction of elevated extensions and ele vated third tracking and other improvements, was .met by the two companies on their re
spective systems. Despite the substantial con tributions by the companies to the expense of subway construction, all subways and elevated extensions of subways are owned by the city, while elevated railroad extensions and third tracking on elevated railroads remain the prop erty of the companies. The dual agreements included leases to the companies of the lines to be operated by them and their subsidiaries.
In Boston a commission appointed on be half of the city constructs the road by con tracts as cheaply as possible and makes a lease to the company owning and operating the sur face and elevated lines at a figure that will at least return to the city the interest that the city has to pay. In the case of both New York and Boston the profit that the municipality reaps is the securing of the construction of rapid transit lines necessary for the development of the city.
In 1918 the Boston operating company found itself in financial difficulties due to a variety of causes and appealed for aid to the State legisla ture. An act was passed by the latter body vesting a board of five trustees with power to operate the Boston system and to fix the fare rate. For the first six months of control by the board from 1 July 1918 the success of the experiment was questionable. The fare has since been increased 100 per cent and agitation for public operation has decreased proportion ately. Boston's subway now extends to all parts of Greater Boston and to Cambridge, Mass.
In Paris the city arranged with a corporation especially organized for the purpose, the leasing of all lines that the city of Paris might build, the company to pay to the city one-third of the gross receipts, and, in addition, to furnish the equipment, which will become the property of the city at the end of the lease without pay ment. The city of Paris then constructs in its own name the several lines, which must con form to a certain standard of excellence. The company has no supervision of the construction of the lines, as it is not directly interested in the cost. The city of Paris is not secured against loss, as in the case of New York and Boston, but, on the other hand, being practi cally a partner in the enterprise, it can secure a direct monetary profit, provided the roads are profitable in their operation, which have so far been found to be the case. Chicago and Phila delphia are building subways, construction is well advanced in the latter city. Chicago pro poses to spend $100,000,000 in a nine-year build ing plan, involving the construction of a double track rapid transit subway six miles in length and a five-mile subway for street surface cars. These subways would be the nucleus of a larger system to be constructed later, which provides for 58.1 miles of subway. Consult Beavan, A. H., 'Tube, Train, Tram and Car' (New York 1903) ; McPherson, L. G., 'Transportation in Europe> (New York 1910) ; Johnson, E. R., 'Elements of Transportation' (ib. 1909). See also TUNNELS AND TUNNELING.