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a complex of installations and devices forming a road with guiding rails for the movement of railroad rolling stock.
The main elements of railroad track are the upper structure of the right-of-way, the roadbed, and artificial structures (such as railroad bridges, tunnels, viaducts, drainpipes, and retaining walls). The distance between the rails is not consis-tent throughout the world: it varies from 1,676 mm (in India, Spain, Argentina, Chile, and elsewhere) to 1,520 mm (in the USSR), 1,435 mm (in most European countries, Canada, and the USA), 1,067 mm (in Japan, Indonesia, and some African countries), and other gauges (for example, 1,000 mm, 914 mm, or 891 mm). The plane of the track is a projection of the axis of the track onto a horizontal surface, and the longitudinal profile is a vertical cross section along its axis. The plane and profile determine the route of the track (the position of the axis of the track in space). The railroad track consists of straight and curved sectors, which can be level or inclined. Rolling stock passes smoothly from tangent onto a curve by means of transition stretches with gradually increasing radii. The best conditions for train traffic are created when the track is level. A ruling grade, a dangerous grade, and a safe grade are differentiated. A ruling grade determines the weight of a freight train for a line (for a trunk line the grade may not exceed 0.6 percent; for others, 0.9 percent). A dangerous slope is one on which braking is required; on a safe slope, braking is not required.
Station tracks, sidings, and passing tracks are usually sited on flat areas with grades not in excess of 0.25 percent.
The condition of railroad track is constantly checked to ensure uninterrupted and safe traffic. As speeds, freight volume, and axle loads on rolling stock increase, heavier rails are laid, sturdier ballast is put down, and reinforced-concrete ties and continuous reinforced-concrete footings in the form of frames and panels are used. The number of joints is being reduced to improve track and rolling stock operations, resulting in jointless track composed of lengths of welded rail as long as several km (up to 800 m is customary in the USSR).
V. I. TIKHOMIROV
two rails, or rail lines, that are placed at a certain distance from each other and attached to the supports, or sleeper, of a railroad line with rail fastenings.
The normal width of a straight track—the rail gauge—is 1,435 mm in most countries; in the USSR it is 1,520 mm, with a tolerance of +6 and -4 mm. In straight sections the two rails must be on one level (±4 mm). Where the railroad line curves, the outer rail is higher than the inner rail in order to distribute the load equally on both rails, to reduce the lateral force of the wheels on the outer rail, and to lessen the effect that excessive and unattenuated horizontal acceleration can have on the passengers.
In addition to railroads with normal gauge, there are those with narrow-gauge tracks. A standard narrow-gauge line has a width of 750 mm, while a nonstandard narrow-gauge line has a width of 1,000 mm; the latter is less frequent. The sidings to industrial enterprises, shafts, and mines is usually a narrow-gauge line.