Wooden, cast iron or R.C.C members which are laid transverse to the track alignment to support the rails and to transfer the load from the rails to the underlying ballast are called sleepers.
In a railway track, sleepers perform the following functions:
- To hold the rails to proper gauge in all situations. i.e. exact gauge along straights and flat curves, slightly loose on sharp curves and slightly tight in diamond crossings.
- To support the rails firmly and evenly throughout.
- To distribute the load transmitted through rails over large area of ballast underneath or to the bridge girders.
- To hold the rails to proper level in turnouts and crossovers, and at 1 in 20 in ward slope along straight tracks.
- To provide and elastic medium between the rails and ballast and also to absorb the vibrations caused due to moving axle loads.
- To maintain proper alignment of the track. On curves proper cant is provided by raising the outer rail and tamping the required quantity of ballast bellow the rails.
- To provide the general stability of the permanent way throughout.
- To provide the insulation of track for the electrified for signaling.
- To provide easy replacement of the rail fastenings without any serious traffic disturbances.
