K. RAILWAYS - FOREIGN AND CONTINENTAL (cont.)
Railways - United States - Construction
The low cost of American railways has been due largely to a close adaptation of the alignment to the natural surface by the use of grades and curves. The importance of saving in materials, labour, and cost has been very much greater than in Europe, because labour and nearly all materials but timber were much costlier, and especially because the interest on money was very much higher,until about 1875, on the average probably 9 or 10 per cent. The use of the "truck" or "bogie" under locomotives and cars made it possible for the Baltimore and Ohio Railroad, the first long line in a mountainous country, to be constructed with curves of 600 feet radius, and on temporary lines on the same railway with curves of 300 and 278 feet radius. Curves of 955 and even 716 feet radius are common through difficult country; curves of 573 feet radius occur on some important lines; and 410 to 383 feet radii are not uncommon in mountainous regions. On the United States military railroads in 1864 an immense traffic passed safely over temporary lines with a curve of 50 feet radius. Early experiments as to the real power of the locomotive to surmount gradients led to the adoption of 110 and 116 feet per mile for ascents 17 miles long, and to the successful use on a temporary track over a tunnel (in 1852) of gradients of 1 in 10, over which a locomotive weighing 25 tons hauled regularly one-car trains weighing 53 1/2 tons, including its own weight. A gradient of 1 in 12 1/2, 7 miles long, in a mining branch in Colorado is now regularly worked. In the construction proper a noticeable peculiarity has been the free use of open trestle-work of timber, to save both masonry and earth or rock excavation. Some of these timber structures have been of enormous proportions, as the Portage Viaduct (see vol. iv. p.328) over the Genesee River, which was destroyed by fire in 1875. It was 234 feet high and 800 feet long in 50 feet spans, and contained 125,000 cubic feet of timber and 80 tons of bolts. Structures of timber exceeding 100 feet in height have been rare, but of all dimensions below that exceedingly common, the usual intent and practice having been to replace them as they became unserviceable with masonry embankments. Although their use has not unfrequently been abused by permitting them to become unsafe from decay, they have in the main been thoroughly solid and substantial. For bridge spans of 30 to 250 feet the wooden "Howe truss" bridge, a type peculiar to America, was early invented and almost universally used where wrought-iron trusses would be now used both in Europe and America. The piers and abutments for such trusses were usually of stone, but not unfrequently of timber also. These wooden trusses are now being rapidly replaced with iron, the leading types being the Whipple, Post, Fink, and Bollman trusses (see BRIDGES, vol. iv. p. 322 sq.). The sleepers (in America called ties or cross-ties) are usually of hard wood (white oak), hewn on top and bottom, with the natural surface of the tree on the sides. The usual dimensions are 6 (sometimes 7) inches thick, 8 (sometimes 8 1/2 or 9) feet long, and 8 to 10 or even 12 inches face. The usual rule is to place them 2 feet or less apart, and 2640 to 2700 to the mile. The large bearing surface thus afforded has especially favoured the use of the flat-based or Vignoles rail, and it is in exclusive use throughout North and for the most part South America. The rails now most largely rolled weigh from 56 to 65 lb. per yard. On the light-traffic lines of the south and west there are still many 50 lb. rails, and in the north and east rails of 70, 72, 75, and 80 lb. sections are in limited but increasing use. An average for the whole United States would now be somewhat under 60 lb. The close propinquity of the sleepers gives much greater stiffness to the rail than comparative weights alone would indicate, a 60 lb. rail being fully equivalent in stiffness and strength to an 80 lb. rail supported on chairs 3 feet between centres. The ballast and drainage of American railroads have often been very defective, with the view to effecting a large saving in first cost. Improvements in this as in other respects have taken place in recent years, and many thousand miles are now maintained at a high standard of excellence. Right of way, usually in continuous strip 100 feet wide (wider where necessary, but never narrower), has been largely given, or purchased at very low rates. The widths of road-bed (almost always first graded for a single track) are usually 18 to 20 feet in excavation and 14 feet on embankments, with 1 1/2 to 1 slopes. Side slopes of 1 to 1 have been largely used in regions not exposed to frost. Parallel tracks are placed 13 feet between centres.
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