state sources, mostly wind generated electricity from Minnesota and Iowa. The state has agnostic policies for developing wind power in state. Transportation Airports Wisconsin is served by eight commercial service airports, in addition to a number of general aviation airports. Milwaukee Mitchell International Airport is the largest international commercial airport located in Wisconsin. Intercity bus service Wisconsin is served by multiple intercity bus operators, which provide service to 71 stops and 53 cities. Major highways The Wisconsin Department of Transportation is responsible for planning, building and maintaining the state's highways. Eight Interstate Highways are located in the state. Rail service Amtrak provides daily passenger rail service between Chicago and Milwaukee through the Hiawatha Service. Also provided is cross-country service via the Empire Builder with stops in several cities across Wisconsin. Commuter rail provider Metra's Union Pacific North (UP-N) line has its northern terminus in Kenosha, the only Metra line and station in the state of Wisconsin. The Hop, a modern streetcar system in Milwaukee, began service in 2018. The 2.1 mile (3.4 km) initial line runs from Milwaukee Intermodal Station to Burns Commons. The system is expected to be expanded in the future. Important municipalities Over 68% of Wisconsin residents live in urban areas, with the Greater Milwaukee area home to roughly one-third of the state's population. With more than 590,000 residents, Milwaukee is the 30th-largest city in the country. The string of cities along the western edge of Lake Michigan is generally considered to be an example of a megalopolis. With a population of nearly 260,000, Madison is consistently ranked as one of the most livable cities in both the state and country and is the fastest-growing city in Wisconsin. Medium-size cities dot the state and anchor a network of working farms surrounding them. As of 2011, there were 12 cities in Wisconsin with a population of 50,000 or more, accounting for 73% of the state's employment. Wisconsin has three types of municipality: cities, villages, and towns. Cities and villages are incorporated urban areas. Towns are unincorporated minor civil divisions of counties with limited self-government. Education Wisconsin, along with Minnesota and Michigan, was among the Midwestern leaders in the emergent American state university movement following the Civil War in the United States. By the start of the 20th century, education in the state advocated the "Wisconsin Idea", which emphasized service to the people of the state. The "Wisconsin Idea"