New air conditioned trains, which have been running on the Metropolitan line for the last couple of years, are now being introduced on the Hammersmith & City line and later this summer on the Circle line.
The two lines will be fully served by the new trains by the end of next year and, by 2016, an air conditioned service of 191 trains will be in operation covering 40 per cent of the Tube network.
For people using two of London's busiest Tube stations, Green Park and Oxford Circus, station cooling systems that were installed last year have made a significant difference by reducing the temperature at platform level say TfL.
Other work to improve ventilation shafts, restore out of service fan systems and portable fans will also be helping to keep passengers cool.
More top news
Scotland Yard said the male youths will appear in custody at Westminster Magistrates' Court on Saturday.
The family of Oliver Dearlove urged people to "think again" before using their fists, as the man who killed him began a six-year jail term.
London Fire Brigade took Southwark Council to court on four charges in relation to safety breaches at Lakanal House in Camberwell.