"Tom Barry" wrote in message

Regen braking has a place here, too, if
you can shove the heat from the necessary resistors outside.

Quite apart from the fact that the resistors aren't likely to be needed
much in the central underground sections where there are lots of other
accelerating trains, I assume they put out no more heat than the
friction brakes would have done. They're more likely to be needed on the
extremities of the network where there may not be many other trains
around to absorb the power.