On railways, the axle load is the maximum weight of a train per pair of wheels allowable for a given section of track. The maximum axle load is related to the strength of the track, which is determined by weight of rails, density of sleepers and fixtures, train speeds, amount of ballast, and strength of bridges. Because track and especially the rails are expensive, it is desirable to optimise the track for a given axle load. If the track is overloaded by trains that are too heavy, it can be destroyed in a short time. It is convenient for the steelworks that rails are made in a limited number of sizes, so that a perfect match of rail weight and axle load is rarely achieved. New rail is often reserved for heavy main line use, which release good but lighter rail which can be cascaded for lighter duties on branch lines. The lightest rail cascaded from the lightest branchlines may have no railway use other that for structural items such as fenceposts, telegraph posts and for reinforcing concrete. In rail transport, a train consists of a single or several connected rail vehicles that are capable of being moved together along a guideway to transport freight or passengers from one place to another along a planned route. ... The word track can mean more than one thing. ... An axle is a central shaft for a rotating wheel or gear. ... Sleeper has a number of different meanings, usually connected to sleep in varying degrees of literalness: Sleeper is a Woody Allen movie. ... Ballast may mean: track ballast: gravel or cinders forming the railroad or railway track-bed on which sleepers (ties) and track is laid, for proper drainage ships ballast: water, sand, rocks, or bricks used to weight a ship down when it has very little cargo (though water may contain...

Roads

The term axle load is also applicable to trucks which is complicated by the fact that trucks may have more than two wheels per axle.