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Joints | Joint Track | British RailroadBecause each joint is a relatively weak spot in a track, design engineers have reduced the number of joints by lengthening the rails. The customary length when locomotives were introduced was 0.9 m (3 ft), but in the 1830s this was increased to 4.6 or 6.1 m (15 or 20 ft). Early in the 20th century the most common length for rails was 9.1 m (30 ft), and this figure soon became 10 m (33 ft) when 12.2-m (40-ft) freight cars came into general use. To some extent the length of rails has been limited by difficulties in transporting them. Rails 18.3 m (60 ft) long, used on one British railroad as early as 1894, were installed on some United States railroads, others of which have 13.7-m (45-ft) rails (Joints, Joint Track, British Railroad). In the United States rails are often butt-welded together to form lengths as long as 0.4 km (0.25 mi). At first this was done cautiously for fear that expansion and contraction due to temperature changes would cause buckling in great lengths of continuous rail. Experience showed, however, that longitudinal expansion and contraction are not excessive and need not lead to buckling. Techniques were developed for making butt welds as strong as the rails themselves. Where welding is not used, rails are joined by bars bolted to the sides so as to cover the joint. Stevens is credited with inventing the first such joint. On earlier railroads using metal rails, the individual sections were not fastened together in any way (Joints, Joint Track, British Railroad). Advances in track construction in the 20th century included using longer and stronger joint bars and wider tie plates to spread the weight of trains more evenly on the ties. Tie plates with shoulders to brace the rail on either side are used, and nearly all U.S. railroads have special braces called anticreepers, designed to prevent longitudinal displacement (Joints, Joint Track, British Railroad). Beginning in 1925 and continuing at an accelerated rate after that, especially after World War II (1939-1945), the installation of centralized traffic control (CTC) increased track capacity on many railroads and lessened or even eliminated the need for additional pairs of rails. In this system the switches and signals over many kilometers of track are controlled by a single train dispatcher who sits before a panel or switchboard in a control room. On this panel the location of each train is shown automatically on an illuminated diagram. Below the diagram are knobs that control each signal and levers that control each switch on the line. Many railroads began to remove extra main-line tracks after the installation of CTC (Joints, Joint Track, British Railroad). Joints | Joint Track | British Railroad |
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Joints | Joint Track | British Railroad |
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GOVERNMENT REGULATION OF RAILROADS: • INTRODUCTION • STATE REGULATION • FEDERAL REGULATION • EARLY 20TH-CENTURY REGULATION • THE DEPRESSION YEARS • POSTWAR ENACTMENTS • DEREGULATION MOVEMENTS |
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