Personal transportation is dominated by automobiles, which operate on a network of 4 million miles (6.4 million kilometers) of public roads.[377] The United States has the world's second-largest automobile market,[378] and has the highest vehicle ownership per capita in the world, with 816.4 vehicles per 1,000 Americans (2014).[379] In 2017, there were 255,009,283 non-two wheel motor vehicles, or about 910 vehicles per 1,000 people.[380]
The civil airline industry is entirely privately owned and has been largely deregulated since 1978, while most major airports are publicly owned.[381] The three largest airlines in the world by passengers carried are U.S.-based; American Airlines is number one after its 2013 acquisition by US Airways.[382] Of the world's 50 busiest passenger airports, 16 are in the United States, including the busiest, Hartsfield–Jackson Atlanta International Airport.[383]
The United States has the longest rail network in the world, nearly all standard gauge. The network handles mostly freight, with intercity passenger service provided by Amtrak to all but four states.[384]
Transportation is the largest single source of greenhouse gas emissions in the United States. The country ranks as the world's second-highest emitter of greenhouse gases, exceeded only by China.[385] The United States had been the world's largest producer of greenhouse gases and ranks third, tied with Canada, for greenhouse gas emissions per capita.[386]