technology, such as computers, satellite communication, and the internet, have contributed to many improvements within the industry. These developments have increased the productivity of company operations, saved the time and effort of drivers, and provided new, more accessible forms of entertainment to men and women who often spend long periods of time away from home. In 2006, the U.S. Environmental Protection Agency implemented revised emission standards for diesel trucks (reducing airborne pollutants emitted by diesel engines) which promises to improve air quality and public health. Roadway links with adjacent countries and non-contiguous parts of the United States Within the United States: Alaska – Yes, via Canada and the Alaska Marine Highway in Washington Hawaii – No. American Samoa – No. Guam – No. Northern Mariana Islands – No. Puerto Rico – No. U.S. Virgin Islands – No. With adjacent countries: Canada – Yes. Mexico – Yes. Russia – No, but proposed via Bering Strait crossing Cuba – No. Since the American embargo against Cuba, car ferry service from Florida and New Orleans to Havana ceased in 1962. Bahamas – No, but ferries travel to the Bahamas Traffic codes Each state has its own traffic code, although most of the rules of the road are similar for the purpose of uniformity, given that all states grant reciprocal driving privileges (and penalties) to each other's licensed drivers. Air transportation The United States has advanced air transportation infrastructure which utilizes approximately 5,000 paved runways. In terms of passengers, seventeen of the world's thirty busiest airports in 2004 were in the United States, including the world's busiest, Hartsfield-Jackson Atlanta International Airport. In terms of cargo, in the same year, twelve of the world's thirty busiest airports were in the United States, including the world's busiest, Memphis International Airport. Private aircraft are also used for medical emergencies, government agencies, large businesses, and individuals, see general aviation. There is no single national flag airline; passenger airlines in the United States have always been privately owned. There are over 200 domestic passenger and cargo airlines and a number of international carriers. The major international carriers of the United States are Delta Air Lines, American Airlines, and United Airlines. Low-cost carrier Southwest Airlines operates few international routes, but has grown its domestic operations to a size comparable to the major international carriers. There is currently no government regulation of ticket pricing, although the federal government retains jurisdiction over