From the lower flange of a suspended !; runway, made of a single I section, run wheels, from the axles of which the transporter is suspended.
The first railway carriages in England had four wheels with two axles, and this construction is still largely employed, especially for short-distance trains.
In whatever form energy is produced and distributed to the train it ultimately appears as mechanical energy applied to turn one or more axles against the resistance to their rotation imposed by the weight on the wheels and the motion of the train.
If the energy supplied is distributed between several axles the relation becomes l l 2 3 w 3.