Today’s invention is a train in which every other carriage has no wheels.
It is instead coupled to its nearest neighbour carriages by a large hinge at either end. These support the weight of the carriage and its occupants as the train passes along the track.
The unwheeled coaches can be made much more like aircraft cabins: strong but not made of Victorian ironwork.
This arrangement greatly lessens the mass of the entire train, whilst leaving unaffected the weight of the engine(s) which are necessary to achieve frictional purchase on the rails.
Naturally, a huge saving in fuel cost is anticipated due to avoiding having to accelerate all that undercarriage mass.