Official Press statement:

The new The Legend of Zelda™: Spirit Tracks game that Iwata announced will utilise the intuitive touch control of Phantom Hourglass in an all new adventure that will please longtime Zelda™ fans while keeping the game accessible to all DS owners. The concept behind this Zelda game includes utilising a steam locomotive to travel around the world, switching Phantom and Link to explore the dungeons, and solving puzzles using new items.