The New York Rapid-transit Subway

10 PARSONS ON NEW YORK RAPID-TRANSIT SUBWAY. [Minutes of New York Central and the New Haven Railroads. By omitting certain ventilators on the roofs and making other slight alterations in design, which would not affect the serviceability, it was possible to run such a car in a subway whose clear height from the base of the rail to the under side of a flat roof was 13 feet. The internal diameter of a tube of corresponding capacity would be 15 feet fl inches. Figs. 21, Plate 6, show the car to be of more generous pro- portions than similar cars on the London tubes, except those on tlie Great Northern and City Railway, which are substantially similar. Allowing 9 feet 6 inches as the overall width of the cars, and pro- viding a generous clearance and space for inspectors to stand if caught between passing trains, a width of 12 feet 6 inclies between the track-centres on the straight was adopted. For four tracks there was thus a clear width of 50 feet between the walls. The depth was controlled by the conduit-yokes of the surface tramways, which are 30 inches high. This distance fixed the minimum cover, which actually averaged about 6 feet. The shallowest distance from street- surface to rail-level was 17 feet. Methods of Construction. Various studies were made as to the best form of roof-construction, and full plans were prepared for spanning the whole width with girders without intermediate supports, and with such supports in the form of either one row of columns between the centre tracks or a row of columns between each pair of tracks. Further studies were made as to the columns themselves, to determine whether they should be placed beneath every girder ; whether they should support a continuous girder and therefore be at intervals longer than the cross- girder intervals ; or whether this continuous girder should be cut into sections, to be supported on two columns set back from the ends, the ends of the longitudinal girders being cantilevers. The long girders spanning all the tracks without columns, while providing a subway attractive to the eye, had the disadvantage of being the most expen- sive form of construction. They depressed the rail-level on account of the greater depth of girder required, and involved the handling of large and heavy girders under busy streets. If intermediate columns were to be used, a continuous longitudinal girder carried by columns at economical intervals presented two objections. First, the longitudinal girder was subject— at least during construction—to variations in temperature, which would bring about difficulties in making closures; secondly, these longitudinal girders would vary with tlie gradient and would all be