You may already have noticed changes to the Metropolitan line, where our upgrade involves new trains, tracks and signalling.
We've introduced a brand new fleet of fully air-conditioned trains to the line, the first in 50 years.
They have more spacious walk-through carriages and, to help you during your journey, the trains are fitted with visual displays and feature automated station announcements. There's also the reassurance of CCTV.
In 2011, we agreed a new contract - our biggest ever - to deliver a new, modern, centralised system on the Metropolitan line, together with the Circle, District and Hammersmith & City lines for 2018. This state-of-the-art system will replace a number of older systems, including manual signalling dating back to the 1920s at Edgware Road.
We know it's not something you see or take much notice of, but new signalling will allow us to run more trains, more often and with fewer failures. Combined with bigger trains that we can move more quickly and closer together, it'll mean more room - or capacity - on the line.
That's good news because as London keeps growing there'll be more people using the Tube. When the upgrade is complete the line capacity will increase by 27 per cent, which means we'll be able to carry about 9,500 more people an hour.
See what the new Metropolitan line trains look like.
Kings Cross St. Pancras
In 2010, we completed a massive redevelopment of King's Cross St. Pancras that quadrupled the size of this key station.
It already sees more passengers a year than Heathrow Airport, with more than 100,000 people passing through the station at peak times every day.
King's Cross St. Pancras is now modern and spacious, has step-free access to all lines, and is less congested thanks to new ways to enter and exit the station.