Given that the trains are reported to be the largest sources of heat, the best solution in the long term will be new, more efficient trains. New drivetrain tec

Given that the trains are reported to be the largest sources of heat, the best solution in the long term will be new, more efficient trains. New drivetrain technology is already far more efficient, producing less waste heat, than the decades-old stuff still being use on most London Underground lines. In new trains, more powerful regenerative braking rather than friction braking will dramatically reduce heat produced from braking, for example. (It will mean less dirty air on the Underground, too!)