Determined to have the "world's largest" everything by 2010, China recently unveiled the "world's largest" bus, The 25-meter-long “Superliner” at Shanghai’s Busworld Asia 2007 convention has five doors, 40 seats, carries up to 300 passengers and, according to a driver, “is flexible when cornering.”
(The linked site has great little slide show a short way down the page.)
One wonders whether they may go one better with another deck on top
