"Andy" wrote

The current used by the system is NOT the amount of waste heat
generated by the train. You keep mentioning the power consumption, but
this has nothing directly to do with the amount of waste heat
generated by the trains (for a given design it will be related of
course, but not between designs). I have never said that the trains
will be consuming less power, just trying to point out that the power
will be used much more efficiently in a modern electrical system than
it was in a 1960s design.

The electrical energy introduced into the system does end up as heat. It
might on the way be used to accelerate the train, converting electrical
energy into kinetic energy, but this will all end up as heat, whether
through friction or braking. If regenerative braking puts electrical energy
back into the system, this reduces the electrical energy introduced into the
system.

Essentially all the electrical energy ends up as heat, and has to be removed
from the system through ventilation. You can't break the First Law (of
Thermodynamics).

Peter