The sleeper is the part of the track on which the rails rest. Its functions are :
(a) To hold the rails to the correct gauge.
(b) To transmit and distribute to the ballast the load imposed by the train traffic running on the rails.
The materials commonly used for sleepers are :
(b) Cast Iron
(d) Pre-stressed Concrete
In view of the shortage of forest resources, timber sleepers are being discontinued. The most popular sleeper now is the pre-stressed concrete sleeper. These have long life and are being manufactured under factory conditions with good quality control.
The sleeper density is usually expressed as M + 1, M + 2, M + 3 and so on per rail length, where M is the length of the standard rail in metres. For high speed BG routes, a sleeper density of M + 9 (with 13 m rails) is followed.