[keyshapegeo99]

Your point about air-conditioning is mistaken. The Jubilee line can be very unpleasant in the summer months as it is not air-conditioned.

The Metropolitan line, by contrast (the oldest Tube line and first metro line in the world, serving as the concept's namesake) is now air-conditioned - as are quite a few other older lines. The Piccadilly, Bakerloo, Waterloo and City, and Central lines are all slated to receive air-conditioning within the next 5 years. (Although the inevitable delays in delivery will probably push this back a bit.) There are no plans to add it to the Jubilee line.

[nly]

The air conditioning on the new Piccadilly Line trains won't be great as they're still limited by the thermal constraints of narrow tunnels and hot clay.