London will soon be the world’s first city to offer contactless card payment for public transportation fares across an entire metro transit program.

By the end of 2012, passengers will enjoy the convenience and security of paying for Tube, bus, tram and train fares using contactless smart cards. Transport for London (TFL) is aiming to have the new system in place in time for hosting the 2012 Summer Olympics.
TFL will upgrade card readers to take advantage of existing infrastructure. It is also looking into expanding the program to include international rail services that depart and arrive in London.
Read more about cashless payment transit cards.