aircraft safety, pilot training, and accident investigations (through the Federal Aviation Administration and the National Transportation Safety Board). The Transportation Security Administration provides security at airports. Rail Passenger Passenger trains were the dominant mode of transportation until the mid-twentieth century. The introduction of jet airplanes on major U.S. routes and the completion of the Interstate Highway system accelerated a decline in intercity rail passenger demand during the 1960s, resulting in the sharp curtailment of passenger service by private railroads. This led to the creation of National Railroad Passenger Corporation (branded as Amtrak) by the federal government in 1971 to maintain limited intercity rail passenger service in most parts of the country. Amtrak serves most major cities but, outside of the Northeast, California, and Illinois, often by only a few trains per day. Amtrak does not serve several major destinations, including Las Vegas, Nevada, and Phoenix, Arizona. Frequent service is available in regional corridors between certain major cities, particularly the Northeast Corridor between Washington, D.C., Philadelphia, New York City and Boston, between New York City and Albany, around Chicago, and in parts of California and the Pacific Northwest. Private intercity rail ended in the United States in 1983 with the discontinuation of the Rio Grande Zephyr, until Brightline started in South Florida in 2018. The state-owned Alaska Railroad is the only other intercity passenger railroad still operating. It has only rail ferry connections with other railroads. Rapid transit There are 15 heavy rail rapid transit systems in the United States. The New York City Subway is the largest rapid transit system in the world by number of stations. Cargo The United States makes extensive use of its rail system for freight. According to the Association of American Railroads: "U.S. freight railroads are the world's busiest, moving more freight than any rail system in any other country. In fact, U.S. railroads move more than four times as much freight as do all of Western Europe's freight railroads combined." Nearly all railroad corridors (not including local transit rail systems) are owned by private companies that provide freight service. Amtrak pays these companies for the right to use the tracks for passenger service. There are approximately 150,000 mi (240,000 km) of mainline track in the United States—the world's longest national railroad network. See List of United States railroads Rail freight has a major national bottleneck in Chicago and the Midwest (about one-third of the