The New York Rapid-transit Subway

12 PARSONS ON NEW YORK RAPID-TRANSIT SUBWAY. [Minutes of to avoid excessive depths in the subway on the north and south sides of the valley, the rails emerged at 122nd Street on the south and again entered the subway on the north at 135th Street. The railway, as constructed, includes all types of urban construction—by cut-and-cover, by tunnelling in rock, in soft ground, in subaqueous material under compressed-air, and by shield ; and by open cut, em- bankment and metal viaduct. The total mileage of construction is divided among these several types as follows:— Table III.—Miles of Various Types of Construction. Contract No. 1. Contract No. 2. Total. Miles. Miles. Miles. Cut-and-cover 12-1 2'1 14-2 Tunnel 3'8 0-1 3’9 Iron lined tubes, single track 0-0 2-6 2-6 „,, ,, double track 0-1 0-0 0-1 Open cut 0'2 0’0 0-2 Embankment between masonry walls 0'2 0'0 0-2 Steel viaduct 6-2 0-0 6’2 Total . . . . 22-6 4-8 27'4 It will be noted that the above totals exceed the miles of route previously given. This is due to the fact that the line beneath Murray Hill is divided into two tunnels of two tracks each, and that the line under a portion of Battery Park, East River, and Jerolemon Street in Brooklyn consists of two single-track tubes. Of the 14’2 miles of cut-and-cover, 13 miles have a flat roof, and 1'2 mile has an arched roof. In making the detailed design, certain assumptions had to be made in regard to loading. The live loads that may be imposed upon the roof of a subway are of three kinds: rolling loads of heavy vehicles such as traction-engines or tramcars; the shock of falling walls, as the result of fires ; and piles of building-, paving-, or other material. The depth of cover, even at the minimum, was enough to distribute the concentrated loads of heavy vehicles over a sufficiently wide area to make the effect upon the roof-beams of less intensity than could reasonably be assumed for the effect produced by either of the other classes of loading. It was also evident that the amount of loading would vary considerably according to the district traversed, being heavier in the commercial districts where there might be a great concentration of material piled in