Engineering Wonders of the World
Volume I

THE NEW YORK SUBWAY. 343 subway — and this meant going along under the streets rather than cutting through cellars and foundations. The choice then narrowed down rapidly. The objective was to bring the business district at the south end of the island into communication with the residential sections of the north end and the mainland to the east (Bronx Bor- ough). Therefore the line was . branched east and west at about the middle of its length, and is operated by running trains up the west branch (the Broadway line) and the east branch (the Bronx line) alter- nately. Speed was sought for by- providing “ express ” trains (making stops at long inter- vals) and “ local ” trains (with frequent stops). Since these demanded separate tracks, the main part of the line has four tracks. The two branches (above 96th Street) are generally but two tracks wide. Keeping close to the sur- face, the Subway necessarily follows closely the gradients of th© streets through which it runs. Only under the high rocky ridge of Washington Heights in the north part of Manhattan Island, and in one or two minor portions, was this impracticable, and here regular rock tunnel construc- tion was adopted, with a greatest depth of 200 feet below the surface. The shallow depth dictated the type of fied in interesting fashion in two portions. Types of Structure used. Pig. 2.—MAP OF THE RAPID TRANSIT SUBWAY OF NEW YORK CITY. It shows Manhattan Island and parts of Bronx and Brooklyn Boroughs. The subway parallels the four elevated rail- ways. Plans for an additional subway- through the area to the east of Central Park are being developed. The steel-framed box structure to be used—a strong steel and concrete box-like section, quite different from the circular or horseshoe form suited to deep-lying tunnels. The Washington Heights Tunnel, of course, does not use the box form. An important exception also concerns the most northerly parts of the line—the last two miles of the Broadway branch, and three miles of the Bronx branch. These are carried above ground on a steel viaduct, like any other elevated railway. The change was made primarily for econ- omy, and indeed underground construction would be an ex- travagance in open, outlying districts. The view, Fig. 1, taken inside the finished Subway, exhibits the appearance of the normal box type which pre- vails on the main part of the line. Those who wish to see the actual grouping of metal and concrete will find the sketches in Fig. 3 interesting. They may note the ingeni- ously-designed section of the steel columns which support the roof, the strong I-beam framing of the walls, the waterproofing course outside the concrete panelling, etc. Two of the tunnel sections, are also shown in the draw- ing. structure was modi-