5. Energy

5.1 Traction energy

There are two types of traction energy:

• autonomous energy: the machines carry their own fuel on board. This is the most common type of self-propelled vehicle in the world, since 80% are self-propelled. In this case, the infrastructure required is limited to simple refueling stations;

• electrical power distributed along the lines is used directly by the machines. In this case, the infrastructure is very large and costly, so the corresponding investment must be made profitable by high traffic volumes and high efficiency. Electric power is only used by 20% of the world's traction units. Its extension depends on the density of industrialization surrounding the networks.

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