Early American rails sometimes curled up and punched through carriage floors
To save money, early North American railroads nailed thin iron strips on top of wooden rails. The iron worked loose, curled upward and could spear into the floors of passing coaches. Railroaders called them snake heads, and the method was abandoned, though a tramway in North Wales kept iron-topped timber rails in service until 1947.
Britain's first railway, built in 1603 between Wollaton and Strelley in Nottinghamshire, used oak or beech rails about 3 feet long, nailed to wooden sleepers. Nobody joined the rails; neighbouring pieces simply shared a sleeper, and angling them at those points produced rough curves. Gravel packed around the sleepers held them in place and gave horses a path to walk on. About 50 such wooden tramways followed over the next 164 years, until the first iron rails went down at Coalbrookdale in 1767.
Locomotives exposed every weakness. Trevithick's engine at Pen-y-darren in 1804 broke its track and had to be taken off. Engineers then overcorrected, bolting iron rails onto stone blocks in rigid formations, which proved a mistake; track that flexes slightly as a train passes lasts better. Since the 1870s nearly all rails have been steel, and modern busy lines use continuously welded rail. Welding into longer lengths began around 1893, and thermite welding, first used on the Essen tramway in 1899, made it routine, giving quieter and safer rides.
Everyday constraints shaped the hardware. Until the late 20th century North American rails came in 39-foot lengths so they fit inside open gondola wagons about 40 feet long. Rail is graded by weight per length: British and North American lines typically use 115 to 141 pounds per yard, and the heaviest mass-produced rail, 155 pounds per yard, was rolled for the Pennsylvania Railroad. Engineers planning an Arctic iron-mine railway on Baffin Island chose old-fashioned carbon steel rails, since modern alloys turn brittle in extreme cold.
Ballast, crushed stone packed under and around the sleepers, supports them and drains water, but it needs constant tamping. Many high-speed lines, tunnels and metro systems instead lay rails on a continuous concrete slab, which costs more to build and less to maintain.
Source: Railway track
