Air shuttle
An air shuttle is a scheduled airline service on short routes with a simplified fare and class structure. No exact definition exists, but the frequency is usually an hour or less and travel time is typically an hour or less. Network airlines may operate shuttle services as one-class or no-frill services, similar to low-cost airlines. Some shuttles are established by governments, businesses, or organizations which require a high level of service in an otherwise thin corridor. For example, the Federal Aviation Administration's William J. Hughes Technical Center in Atlantic City, New Jersey operates an  air shuttle to ferry FAA employees to and from Reagan National Airport (DCA) near Washington, DC four days a week. Certain markets support commercial shuttles. The pioneer service was the Rio de Janeiro-São Paulo air bridge in Brazil which began 5 July 1959. Other early services include the Eastern Air Shuttle, inaugurated in 1961, which offered no-frills, hourly flights connecting LaGuardia Airport in New York City with Washington National Airport and Logan International Airport in Boston, Massachusetts. Air shuttles increasingly face competition from high-speed rail and many airlines withdraw from the market or reduce service shortly after  competing high-speed rail services start. Present-day commercial air shuttle services include: The busiest air routes in the world involve pairs of large cities in close proximity that rely on air transport due to a lack of high-speed rail, and the distance is large enough to discourage car driving. Several of the airports are on islands without road connection to the mainland.