North America metropolitan area by population in North America: Greater Mexico City. Canada also breaks into the top ten largest metropolitan areas with the Toronto metropolitan area having six million people. The proximity of cities to each other on the Canada–United States border and Mexico–United States border has led to the rise of international metropolitan areas. These urban agglomerations are observed at their largest and most productive in Detroit–Windsor and San Diego–Tijuana and experience large commercial, economic, and cultural activity. The metropolitan areas are responsible for millions of dollars of trade dependent on international freight. In Detroit-Windsor the Border Transportation Partnership study
Streetcars in North America order of opening): In addition, the CityLynx Gold Line, which opened in Charlotte, North Carolina, in 2015 using replica-vintage streetcars (see table of heritage streetcar systems, below), is planned to be converted to modern streetcars in 2020. In 2001, Portland, Oregon, which already had a successful light rail system (MAX), became the first city in North America in more than 50 years to open a new streetcar system served by modern vehicles, with the opening of the Portland Streetcar. It uses low-floor cars built in the Czech Republic, but the system's first U.S.-assembled streetcar was delivered in 2009. The line