In 2010, new S-stock trains were delivered to replace the A, C and D stock trains on the subsurface Lines (Metropolitan, Circle, Hammersmith & City, and District). These have standard air-conditioning, as the subsurface tunnels are large enough to displace the exhausted hot air.
All cars are air-conditioned. Traveling between two cities, you can take in the view through the large windows, and enjoy comfort you won't find in air travel. Most trains also carry a cafe, in which you can order hot and cold snacks, sandwiches, beer and alcoholic drinks, and a wide range of non-alcoholic beverages.
France strongly focuses on energy conservation and sustainability. Since air conditioning requires significant energy to operate, many French people volunteer to limit the use of air conditioning to help reduce the strain on the power grid and lower energy consumption.
With an increased capacity of ten percent and walk-through air-conditioned carriages, the new trains have improved accessibility and are more energy efficient. They are currently undergoing driverless trials in Germany and were also spotted in Austria (they were made in a factory in Vienna).
Wear light clothing. Even if you think you might need to wear a jacket, when you are on the hot Tube, it's likely you'll want to take it off immediately. Heavy, dark, thick clothing will make you more likely to sweat, and hold on to the sweat your body does produce – keeping you hot and clammy for longer.