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
Transportation in North America and on Vancouver Island. The state government of Alaska also operates the Alaska Railroad, which currently does not connect to the North American network. In Canada, rail lines from Labrador City, NL to Sept-Îles, Quebec also currently are not linked to the North American network. There have been proposals in recent years to link the island of Newfoundland to the mainland of North America via a 17 km-long rail tunnel under the Strait of Belle Isle, which would also carry automobile traffic on flatcars, similar to the Channel Tunnel between the United Kingdom and France. This has stalled due to