Interstate 90 (I-90) is an west–east transcontinental freeway and the longest Interstate Highway in the United States at 3,099.7 miles (4,988.5 km). It begins in Seattle, Washington, and travels through the Pacific Northwest, Mountain West, Great Plains, Midwest, and the Northeast, ending in Boston, Massachusetts. The highway serves 13 states and has 15 auxiliary routes, primarily in major cities such as Chicago, Cleveland, Buffalo, and Rochester.