Interstate 90 (I-90) is a transcontinental interstate highway in the United States, serving as part of the Dwight D. Eisenhower National System of Interstates. Extending from Boston, Massachusetts, to Seattle, Washington, I-90 covers approximately 3,104 miles (5,002 kilometers) and serves 12 states: Massachusetts, New York, Pennsylvania, Ohio, Indiana, Illinois, Wisconsin, South Dakota, North Dakota, Montana, Idaho, and Washington. It connects several major cities such as Boston, Buffalo, Syracuse, Cleveland, Chicago, Omaha, Sioux Falls, Billings, Missoula, Spokane, and Seattle. The route also crosses the Appalachian Mountains, the Great Plains, and the Rocky Mountains. I-90 was designated on June 29, 1956, as part of the original Interstate Highway System.