The 1973 trains already used rheostatic braking. The new ones use regenerative braking. https://www.modernrailways.com/article/revolution-piccadilly-line#:~:te

The 1973 trains already used rheostatic braking. The new ones use regenerative braking. https://www.modernrailways.com/article/revolution-piccadilly-line#:~:text=This%20is%20because%20the%20new,this%20is%20some%20way%20off https://www.modernrailways.com/article/revolution-piccadilly.... http://www.trainweb.org/tubeprune/73%20tube%20stock.htm http://www.trainweb.org/tubeprune/73%20tube%20stock.htm