Automobiles are a class of four-wheeled motor vehicles that have been designed for passenger transportation and commonly propelled by internal combustion engines using volatile fuel. They are complex technical systems with numerous design functions, including passenger safety and comfort, fuel economy and engine performance, vehicle handling and stability, and emissions control. These functions are the result of a combination of many subsystems, each with its own specific engineering requirements. Historically, automotive design has been driven by the need to meet consumer demands for larger and faster cars with higher passenger capacities. Consequently, engineering has been often subordinated to questionable aesthetics and nonfunctional styling. Since the postwar era, however, automotive designs have been increasingly driven by technological developments, particularly in engine and drivetrain technologies.

The automobile has profoundly changed the world, making possible many activities that were previously impossible or impractical. Modern life seems inconceivable without a private automobile.

Karl Benz invented the first gasoline-powered automobile around 1885, and other inventors and engineers followed with their own designs. By 1910, automobiles were becoming commonplace. The American carmaker Henry Ford revolutionized automobile production with the introduction of the moving assembly line in his Highland Park, Michigan factory in 1913-1914. He used the assembly line to reduce costs and allow the automobile to become affordable for middle-class families.

The resulting increase in demand for automobiles drove new manufacturers into business. They were helped by a seller’s market for an expensive consumer goods item, the availability of cheap raw materials from the United States, and an extensive system of highways that made it possible to deliver vehicles to consumers in distant areas. The United States also possessed a much greater population and a more equitable distribution of wealth than European countries, ensuring large demand for automobile transportation.

Although the United States is a relatively small country, its huge land area makes it necessary for most people to travel long distances for work and leisure. In addition, its industrial tradition, the lack of tariff barriers between states, and a relative shortage of skilled labor encouraged the mechanization of manufacturing. This led to the development of a great number of automobile-related firms and to the spread of an automobile industry that was unprecedented in its scope and magnitude.

Automobiles are classified by their use, as passenger (cars, buses, taxis), commercial (trucks, tempos) or special purpose (ambulance, fire brigade, police vehicle, etc). The majority of automobiles on the road are powered by petrol/gasoline (petrol engine) but diesel engines are widely employed in trucks and buses and some passenger cars.

The history of the automobile has been a story of great promise, but also of major pitfalls and social problems. The development of the automobile has brought with it traffic congestion and the proliferation of speeding, reckless, and drunk driving. It has contributed to air pollution and a drain on dwindling world oil reserves. It has provided a means for urban dwellers to rediscover pristine natural landscapes, and it has given teenagers freedom of movement and helped couples relax their sexual attitudes.