Sleepers

To hold the rails to proper gauge.
To transfer the loads from rails to the ballast.
To support and fix the rails in proper position.
To keep the rails at a proper level in straight tracks and at proper superelevation on curves.
To provide elastic medium between the rails and the ballast
To provide stability to the permanent way on the whole.

The sleepers should be sufficiently strong to act as a beam under loads.
The sleepers should be economical.
They should maintain correct gauge.
They should provide sufficient bearing area for the rail.
The sleepers should have sufficient weight for stability.
Sleepers should facilitate easy fixing and take out of rails without disturbing them.
They should facilitate easy removal and replacement of ballast.
They should not be pushed out easily of their position in any direction under maximum forces of the moving trains.
They should be able to resist impact and vibrations of moving trains.
They should be suitable for each type of ballast.
If track-circuiting is done, it should be possible to insulate them from the rails