They are already using regenerative braking extensively, according to this article https://www.ianvisits.co.uk/blog/2017/06/10/cooling-the-tube-engineering-hea

They are already using regenerative braking extensively, according to this article https://www.ianvisits.co.uk/blog/2017/06/10/cooling-the-tube-engineering-heat-out-of-the-underground/ https://www.ianvisits.co.uk/blog/2017/06/10/cooling-the-tube...