Type of sleeper on main tracks

Kilometres of main tracks by type of cross-piece since 2006.The rails are generally fixed to raag parts (cross-pieces, side-pieces, pieces of wood) and exceptionally to a solid concrete slab.The cross-pieces have a dual function: keep the two rails in place and thus obtain and maintain the required gauge; support the rails and transfer train loads uniformly to the ballast.On the main tracks there are the following types of sleepers:Wood: Of oak or azobeBeton: two generations, old and newMetal