TRACK CONSTRUCTION. The width of the road bed at the top is from 26 to 32 feet for double track and from 14 to 18 feet for single track on embankment. In cuts the width of roadbed exclusive of ditches is from 28 to 33 feet for double track and from IS to 22 feet for single track. The surface of the roadbed at subgrade is almost invariably crowned at the middle so as to drain off water to the sides. On the top of this crowned surface is constructed the track. This consists of the ballast, the ties, the rails, and their accessories. Ballast is used for four principal purposes: (1) to distribute the load over the roadbed; (2) to form a support for the ties; (3) to provide efficient drainage under and around the ties; and (4) to allow of surfacing and arranging the track without disturbing the roadbed. At this point it is a matter of some interest to note that the term ballast originated iu England when gravel ballast was taken from ships for building tramroads. The materials most generally used for ballast are broken stone, furnace slag, burnt clay, gravel, sand, cinders, and earth, but other materials, as shells and chert, are often used locally. These materials rank in merit about in the order named, but the gravel is the material most used in America and after this comes broken stone. The ballast is usually level with the tops of the ties and about one foot thick, and it is usually shouldered out beyond their ends.
Tics, or cross-ties. as they are often termed, are the transverse wooden sills to which the rails are attached. As stated above, they are imbedded in the ballast. Wood is the almost universal material for ties in the United States, but in other countries metal ties are quite extensively employed. About 55 per cent. of all the ties in the United States are of oak and 22 per cent. are of pine. The remaining 33 per cent. is divided between cedar, chestnut, hemlock, cypress, and other woods. White oak is considered the best wood for railway ties, and ties of this wood have a life of about eight years. Ties are generally from 7 to 10 inches wide, 6 inches thick, and S to 9 feet long, and they are spaced from 18 inches to 2 feet apart in the track. An immense amount of timber is consumed annually for rail way ties, as a brief estimate will demonstrate. Assuming that 2500 ties per mile of track are employed on the average, then the 250,000 miles of railway track in the United States require 625,000,000 ties. The annual consumption is about 76,000,000 ties for renewals and 14,000,000 ties for new construction, a total of 90,000,000 ties or nearly 300,000.000 cubic feet of timber. In view of these figures, it is not surprising that railway managers are finding greater difficulty each year. in securing ties, and that they should be resorting to measures which will cut down the consumption.
One of these measures is to plant trees, but the one most commonly sought is to treat the ties used by some of the various methods for prevent ing or rather for de laying the natural decay. Another re
sort for prolonging the life of ties is to use tie plate-s, which are plates of iron inserted between the top of the tie and the bottom of the rail so as to distrib ute the load over a larger area and thus reduce the tendency of the rail to cut in to the top of the tie. By many engineers it is thought that the ultimate solution of the problem will be the substitution of metal ties. An endless number of forms of metal ties have been tried, but only a few of them have proved successful, although these successful forms have given excellent results in many instances. In Europe, India, Africa, South America, and Mex ico, metal ties are extensively used.
Rails are now universally made of steel and are of the flanged T-section invented by Col. R. L.
Stevens in 1S30. This statement is wholly true of American practice and is generally true of foreign practice. Practically the only exception to the flanged T-seetion is the so-called bull headed rail used in England. This rail has the familiar flanged base of the American rail re placed by another head, the objeet of this de sign being to enable the rail to be reversed when one head has become worn. These bull-headed rails cannot of course be spiked to the ties, and they therefore require cast-iron chairs for their support. Formerly in America nearly every road used a form of rail pecu liar to itself, which differed somewhat in minor dimen sions and details from the rails em ployed by other roads. Recently, however, practice has settled down to the use of a very few standard sections. In America the so-called Am. Soc. C. E. section recommended in 1893 by a special committee appointed by the American Society of Civil Engineers is the one which is most generally used ; in Europe the section by Air. Sandberg is chiefly employed. The ordinary length of rails is 30 feet, but. rails 33 feet, 45 feet. and 60 feet long are used to some extent. The weight of rails per linear yard varies from 65 pounds, which is the least weight economical for ordinary service, to 100 pounds, which is the heaviest rail actually in use in the United States. Generally for ordinary traffic on roads with easy curves and moderate grades a 70-pound or 75 pound rail is used; for heavy and fast traffic and for sharp curves and steep grades the weights used run from SO pounds to S5 pounds, 90 pounds.95 pounds, and 100 pounds. An 80-pound rail of the Am. Soe. C. E. sec tion is 7% inches high, with a head 21/2 inches wide and 11/2 inches deep, a web 35/64 inches thick and 5 inches deep, and a base 5 inches wide. Of the total weight, 42 per cent. is in the head, 21 per cent. in the web, and 37 per cent. in the base.