The New York Rapid-transit Subway

36 PARSONS ON NEW YORK RAPID-TRANSIT SUBWAY. [Minutes of In order to get the subway over a transverse sewer at 22nd Street, the roof of the subway at this point had to be brought to within 30 inches of the surface, the extreme minimum as governed by the depths of the tramway-yokes. It was finally arranged to take up all the sub-surface structures and to relay them according to a systematic arrangement, the north and south mains keeping one plane and the cross mains another. As it was not possible to construct all the junctions directly at the crossing itself, some of the lines of 23rd Street were carried either north or south of that street for a distance of about 100 feet, then crossed over beneath the north and south lines and returned on the other side of the street to a continuation in 23rd Street, depressions in the roof-girders being made for some of the cross connections. The work of readjusting these pipes was carried out at a point where there was not only a large vehicular traffic, but also, during the busy hours of morning and evening, no less than 800 cars per hour crossing the point of inter- section. A temporary roof of timber was built to carry the traffic. The principle of separating the longitudinal and cross lines into separate planes formed the general basis for plans at other places. If pipes were small they were left on top of the subway, there being usually sufficient space to accommodate them thus. If they were large they had to be moved to a new position at one side. The details of beam construction for the roof of the subway afforded easy means of carrying pipes across, as it was determined at the outset that no pipes for either gas or water should be carried beneath the subway. The roof of the subway being close to the surface of the street, there was not, except in special cases, sufficient room between the top of the subway-roof and the bottom of the trolley-conduits to pass between them large mains. By constructing troughs between adjacent cross beams of the subway- roof it was possible to gain about 15 inches of extra depth. These troughs were formed either by placing 3-inch beams on the beam- flanges of the roof-girders, or by placing plates with the ends resting on the flanges of the girders and then covering them with a layer of concrete and waterproofing. Mains up to 15 to 20 inches could then be dealt with, even in extremely shallow places. At places, however, mains of larger diameter were encountered, which had to be carried across the subway; and where it was not possible to lower the roof, tlie large pipes were divided into a series of smaller ones of equal total capacity. As an example of this form of construction may be mentioned the work of dividing two gas-mains, one 36 inches and one 30 inches in diameter, at 65th Street and Broadway, where, by constructing a series of