Page:Popular Science Monthly Volume 92.djvu/860

 Building a Subway Under a Subway

Little do New Yorkers know that they are traveling on a suspended subway even though it is underground

By Howard B. Gates, C. E.

��MANY residents of New York city no doubt remember the time when the possibilities of subways as a means of rapid transit were as little realized as the practical application of the airplane, in its present development, is now considered, to our everyday life. But within the last fifteen years a most wonderful system of subways, comprising more than two hundred miles of under- ground railroad, has been built in New York under enormous difficulties at an expenditure of more than $400,000,000.

Statistics show that nearly 2,000,000 persons are carried by this system every day and that m.ore than seventy-five per cent, of this number seek its ac- commodation between the hours of six and nine o'clock in the morning and be- tween four and seven o'clock in the evening. One of our largest railroad systems, with some 26,000 miles of track and traversing thirteen states, carries but one-third of this number. During "rush" hours, even standing room is at a premi- um, although ten-car trains, each carrying 2,000 persons, are oper- ated under a one-and- one-half-minute head- way, controlled by elab- orate electrical signal and emergency stop de- vices, all of which must operate perfectly to make this service pos- sible.

The difficulty of con- structing such an im- portant and complicated system through any of New York's busy thor- oughfares, loses much in a comparison with the difficulties of Iniilding

���Diagram showing relative locations of the old and the new subways

��such a structure beneath an existing and operating subway, without entering or disturbing the structure above. Al- though the average weight of the subway may not be more than a ton to the square foot, there are points, at the columns for instance, where concentrated loads of two hundred or three hundred tons, together with adjacent heavy and rapidly moving trains, make any dis- turbance to the equilibrium or stability of the temporary or permanent supports a matter of considerable responsibility and concern.

Such a piece of work is now in progress beneath the present Times Square sta- tion at 42nd Street and Broadway, passing diagonally beneath that station for about 250 feet of its length. Any in- terruption to operation at this point would congest the entire system, and yet, under a con- siderable portion of that structure, the original foundations have been supplanted by a complicated system of steel beams and timber supports. Traffic is maintained and the 300,000 persons who use the subway daily at that point do not even know what is going on beneath them. The new struc- ture also has four tracks, two local and two ex- press tracks, and will be operated by the Brook- lyn Rapid Transit Com- pany. Connecting pas- sageways will lead from the transit company's present, recently com- pleted station on Broad- way between 40th and 42nd Streets to the Inter- borough station above

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