Transportation in Minnesota is overseen by the Minnesota Department of Transportation (MnDOT) at the state level and by regional and local governments at the local level. Principal transportation corridors radiate from the Twin Cities metropolitan area and along interstate corridors in Greater Minnesota. The major Interstate highways are Interstate35 (I-35), I-90, and I-94, with I-35 and I-94 connecting the Minneapolis–St. Paul area, and I-90 traveling east-west along the southern edge of the state. In 2006, a constitutional amendment was passed that required sales and use taxes on motor vehicles to fund transportation, with at least forty percent dedicated to public transit. There are nearly two dozen rail corridors in Minnesota, most of which go through Minneapolis–St. Paul or Duluth. There is water transportation along the Mississippi River system and from the ports of Lake Superior.