Automobiles are wheeled motor vehicles, usually with four wheels, designed to run primarily on road systems and for the transport of passengers rather than cargo. They use an internal combustion engine, most often fueled by gasoline (petrol) but sometimes by other petroleum products or even natural gas. They are one of the most widely used and highly developed of modern technologies, as well as a key source of employment in the world.
Passenger cars are the dominant mode of transportation in the world today, with an estimated 1.4 billion vehicles in operation globally. They account for more than three trillion miles (5 trillion kilometres) of travel each year. They have become the primary means of family transportation in many countries, especially the United States where more than 70 million cars are in use. They also form the backbone of a new consumer goods-oriented society, providing one of every six jobs in America and requiring advanced technology in ancillary industries, such as steel and petroleum.
Although the automobile had been around in various forms since the late 17th century, it became practical to mass-produce when Henry Ford introduced his Model T in 1908. His assembly line, in which workers sit at a stationary station doing a single job as parts move by on conveyor belts, revolutionized production and enabled the automobile to be within the reach of middle class families.
In the postwar era, however, engineering in automobiles was subordinated to the questionable aesthetics of nonfunctional styling, and quality deteriorated to the point that by the mid-1960s American-made cars were being delivered to retail buyers with an average of twenty-four defects per unit, a large percentage safety related. In addition, the increasing social costs of air pollution and a drain on dwindling world oil supplies forced manufacturers to work hard at producing vehicles that used less gasoline.