The real puzzle imho is to get people to use public transport for the mostly empty route and time combinations. There are many of those for different reasons. Trains are so heavy it doesnt really cost or save anything if there are people inside or not. Its like restaurants throwing away food.
The UK offers aggressive discounts for advance purchasing tickets on long distance routes at quiet times, which works well.
£80 if I have the audacity to go to greater London today without having planned ahead (3 hour journey + tube). And the same cost coming back - off peak of course. £160! Vs £55 in petrol
Travel at quieter times to benefit from cheaper off peak tickets they used to say. Hah.