Sleepers are the track components resting on the ballast formation transversely. Railway sleepers were first made in timber, and then a limited number of steel sleepers were used, followed by the now popular concrete sleepers. The majority of modern railway sleepers used in world are the pre-stressed concrete sleepers are
- Support and restrain the rail foot.
- Sustain and distribute loads from the rail foot to the underlying ballast.
- Maintain the rail gauge and shape, and preclude rail inclination and track instability.
- Withstand longitudinal, lateral and vertical rail movements.
- Provide insulation between parallel rails, and resist wearing and loading, and endure extreme weather conditions from cold to hot, and from rain to drought.
Due to the rigidity of the cast -in portion of the rail fitting, a concrete sleeper maintains the rail gauge much better than a timber sleeper, where the increase of gauge over the years is an accepted phenomenon. This applies especially to curved track.
