The subway is, of course, perfectly clean, smokeless, and comparatively quiet; neither in the streets can any noise be heard from the cars that are continually passing close beneath. By an extension of the subway under Boston harbour, the surface lines in the district of East Boston are connected with the main system, thus making the entire length eight miles of single track. NEW YORK In New York, after much careful consideration of the advantages and disadvantages of deep tunnels (tubes) and shallow railways, the Rapid Transit Commissioners decided upon the latter as being likely to give the best facilities for quick travelling. On account of its peculiar peninsular shape, admitting of extension in one direction [Illustration: FIG. 24. NEW YORK SUBWAY IN COURSE OF CONSTRUCTION. CAR TRAFFIC MAINTAINED _By permission of the_ _London County Council_] only, the problem of transportation in the Empire City is comparatively easy, the routes being straight, and no necessity existing for intercommunication as in London. But, on the other hand, the number of persons to be carried morning and evening is greater. Instead of the arched roof and masonry side-walks of the ordinary underground, there is a rectangular structure with a framework of steel beams riveted together, concrete enclosing the erection completely at the top and sides, and forming the bottom, rows of steel columns helping to support the roof between the tracks--in other words, a kind of Britannia Bridge let into the surface of the earth. The line has four tracks, the two centre ones being reserved for an express service (30 miles an hour), with stations 1½ miles apart. On the other tracks the stations are closer together, about four to the mile. So that there are two kinds of stations; one with platforms on the outside of the outer (or slow) track (at which only local trains stop), and another with platforms for fast trains only, and island platforms for either local or express trains. At the former stations the subway is sufficiently deep to allow of a bridge over the entire four tracks, with staircases leading to the various platforms. By means of loops, and, in places, by the lowering of the express track beneath the local tracks, crossings and switchings at the termini are, as in the Paris Métropolitain, eliminated, and the cars run continuously without any shunting whatever. Its general scheme is as follows. Starting with a loop round the General Post Office, a four-track route is taken direct to the Grand Central Station in 42nd Street. It then turns west along 42nd Street to Broadway, and proceeds under Broadway to 104th Street, a distance of seven miles. Here the four tracks divide, a [Illustration: FIG. 25. NEW YORK SUBWAY, SHOWING HOW IT WAS BUILT _By permission of the_ _London County Council_]