The Circle, District, Hammersmith & City and Metropolitan lines will all have air conditioned trains by 2016.
Introducing the new trains is possible because these lines operate largely above ground and their tunnels are both larger and closer to the surface than on other lines. Heat generated as a by-product of air conditioning can then escape.
In deeper (and smaller) tube tunnels that heat is trapped. Air conditioning would cool carriages, but make platforms and tunnels even hotter.
We are looking at different approaches to cooling such as lighter, more energy-efficient trains. This would reduce the heat input to the tunnels and allow us to use air-conditioning.
For now a variety of ventilation methods are removing heat from the network, improving air flow and comfort levels for passengers.
We have already upgraded the mid-tunnel ventilation fans between stations on the Victoria line so that twice as much fresh air is drawn in and twice as much warm air expelled.
Large portable fans will be installed at key locations each summer.
We are committed to improving environmental performance across all areas of the business.
The London Underground Environment Report is now included in the Transport for London Environment Report.
We know that how we look after our land is important to those living near us and carry out work with this in mind.
To find out more about how we manage vegetation to ensure it doesn't disrupt services and delay customers, while protecting local habitats, read our How we look after our land question and answer guide (PDF 59KB)
This guide explains the approach we take and aims to answer any questions you might have. If you have questions that are not covered in this guide you can contact us 24
hours a day, seven days a week on 0845 257 78 78 or e-mail firstname.lastname@example.org