Diego, California San Juan, Puerto Rico Savannah, Georgia Seattle, Washington Tacoma, Washington Tampa, Florida Toledo, Ohio Valdez, Alaska Merchant marine Most U.S. exports and imports are on foreign ships. The 1920 Jones Act bars foreign ships from trade within the United States, thus creating a domestic "Jones Act fleet". Deck officers and ship's engineers of U.S.-flagged ships are usually trained at one of the established maritime academies. Military The federal military has a dedicated system of bases with runways, aircraft, watercraft, conventional cars and trucks, and armored and special-purpose vehicles. During times of war, it may commandeer private infrastructure and vehicles as authorized by Congress and the President. Pipeline statistics Petroleum products: 224,620 km Natural gas: 548,665 km (2006) Policy As the population of the world increases, cities grow in size and population – according to the United Nations, 55% of the world's population live in cities, and by 2050 this number is expected to rise to 68%. Public transportation policy must evolve to meet the changing priorities of the urban world. The institution of policy enforces order in transportation, which is by nature chaotic as people attempt to travel from one place to another as fast as possible. This policy helps to reduce accidents and save lives. Pedestrian A key component of a suitable urban environment is support for pedestrian traffic, including people on foot as well as human propelled vehicles like bikes, skateboards, and scooters. Pedestrian policy is implemented at the state level, but consistent across states is the fact that the pedestrian has the right-of-way. If someone on foot is crossing the street, legally or illegally, any vehicular traffic is required to stop—under no circumstance does a driver have a right to hit a pedestrian. The exact details with respect to when a vehicle has to stop differ between the states, some requiring that all vehicles at an intersection yield to a pedestrian, while others requiring only those vehicles perpendicular to the motion of the crossing to stop. California requires all vehicles at an intersection to yield to a pedestrian walking in any direction. There are also rules for pedestrian conduct. Though they have the right-of-way, pedestrians are not permitted to leave a curb into a crosswalk close enough to a vehicle to “constitute hazard.” Pedestrians must also yield to mass transit like light-rail cars and trains, as these forms of transportation operate on a schedule and