Automobiles, or cars as they are more commonly known, are one of the most universal and useful modern technologies. They are four-wheeled vehicles that use internal combustion engines to travel on land. Most automobiles are powered by gasoline, although some use other liquid fuels or even electricity to move the wheels. These vehicles provide transportation for people from place to place, and they also allow people to shop, work, play, visit friends, and go to church. In fact, it is hard to imagine living in the United States without an automobile.

While the technology of the automobile dates back several hundred years, the modern car was first perfected in Germany and France in the late 1800s by engineers such as Karl Benz. These early cars were expensive and were often customized for the buyer. But by 1914, Henry Ford introduced the assembly line, which greatly lowered production costs and made his Model T available to many middle-class Americans. The automobile revolutionized life in the United States. People could go to work and get things done more quickly. Families could spend more time together, as they no longer needed to travel on foot or horseback to reach places far away. Businesses sprang up to serve the needs of the growing automobile industry, including motels, hotels, amusement parks and other recreational activities, restaurants, and fast food chains. And roads became more convenient and safe, as highways replaced old dirt tracks.

The development of the automobile has been closely linked to the development of science and engineering. Engineers have analyzed the mechanical, electrical and aerodynamic properties of vehicles, and new technical developments are continually being employed to improve their performance. In addition, the design of a vehicle depends on its intended use. For example, vehicles designed for off-road use require durable, simple systems with high resistance to severe overloading and extreme operating conditions. Vehicles designed for high-speed, limited-access road systems should be engineered to offer passenger comfort options and optimize high-speed handling and stability.

During the 1920s, the American car manufacturing industry reached a saturation point. Compared to what had come before, there were now few differences in the basic design of a car. By the late 1930s, most major manufacturers were making the same model with only minor variations in appearance and accessories. These models included the self-starter, the closed all-steel body, the high-compression engine, hydraulic brakes, and the syncromesh transmission. During the 1950s, manufacturers introduced air conditioning, automatic transmission, and power steering.