The automobile has been one of the major forces for change in twentieth-century American culture and economy. It accelerated the pace of industry by enabling mass production. It changed everyday life by providing people with greater freedom of movement and by opening up new opportunities for travel and recreation. It created many new jobs in the manufacturing of cars, in the construction of roads and highways and in the development of services such as gas stations and motels. It ended rural isolation and brought urban amenities, such as schools and medical care, to small towns and farm villages. It encouraged outdoor recreational activities and stimulated tourism. The automobile also changed farming and made the traditional family farm obsolete. It led to the development of many ancillary industries and technologies, such as petroleum and gasoline, rubber and then plastics. It became the most important source of consumer goods and an essential part of a new, consumer-goods-oriented society.
The modern automobile is a complex technical system with thousands of subsystems with specific design functions. It is usually propelled by an internal combustion engine using a volatile fuel, such as gasoline or diesel fuel. Its power is transferred to the wheels by a transmission system that may be mechanical or automatic. The power of the engine and transmission is rated in horsepower or kilowatts.
An automobile must have brakes to stop it in an emergency or when parked. Brakes work by friction, and if there is sufficient pressure they can apply hundreds of pounds per square inch (sq. in.). The modern automobile is almost always air-conditioned to provide comfort for passengers during a long trip and to reduce the temperature of the interior.
There are several types of automobiles, depending on the size and capacity of the vehicle, as well as its purpose and intended use. These include the sedan, which has four doors; the station wagon or estate car, which has room for cargo as well as passengers; and the pickup truck, SUV or minivan, which combine the towing capability of a pickup with the passenger-carrying capacity of a sedan.
Automobiles are widely used in the United States and many other countries. Annually, over 5 – 59 million different vehicles are produced worldwide, including trucks and buses. The majority of these are manufactured in the United States, Japan and France. Cars are an important contributor to greenhouse gas emissions and other pollutants that pollute the environment. The United States Environmental Protection Agency estimates that transportation is responsible for 27 percent of greenhouse gas emissions. Drivers can limit the amount of pollution their car produces by purchasing a fuel-efficient model and keeping it properly maintained. They can also avoid generating emissions by walking, riding a bicycle or taking public transportation. A disadvantage of owning a car is dealing with traffic congestion and finding places to park it. However, for many people the advantages outweigh these inconveniences. Having your own car allows you to avoid relying on other drivers for rides, and gives you more control over your schedule.