> indeed, the use of regenerative braking now converts about half the heat loss back into electricity. However, that can only work where trains are accelerating

> indeed, the use of regenerative braking now converts about half the heat loss back into electricity. However, that can only work where trains are accelerating and braking at the same time, on the same electricity sub-station loop. Besides that, Tube tracks often rise slightly at stations, so that trains get a small gravity assist to both stopping and starting off again. (Unfortunately it also means that hot air from the tunnels tends to collect there, but you can't win 'em all.)