The Koshu Kaido is the least-traveled of the three highways which link Edo and Kyoto. Though it is a more direct route, and shorter than either the Tokaido or Nakasendo, it travels over several high mountain passes as it goes through Musashi and Kai provinces, and on to Nagoya, where it rejoins the Tokaido. The rugged terrain makes this route difficult even in good weather, and it can be virtually impassable in the winter. Nevertheless, it is a key highway with both military and commercial importance.