Automobiles, or cars, are the most common means of transportation in most countries and communities. They are a large industry and provide jobs for thousands of people worldwide. In the United States alone, there are more than 73 million automobiles on the roads and byways. They are powered by internal combustion engines fueled most commonly by gasoline but sometimes by diesel fuel, kerosene, or other petroleum products. Trucks, buses, and limousines are also automobiles, but they are much larger than the average car.
The modern automobile combines many technical systems with specific design functions. Many of these subsystems have evolved from breakthroughs in the technology of electronic computers, high-strength plastics and new alloys of steel and nonferrous metals. Others have resulted from new legislation concerning automobile safety and pollution control, or from consumer demand for a more functionally designed, less expensive, and fuel-efficient automobile.
In the nineteenth century, German and French engineers such as Gottlieb Daimler, Karl Benz, and Nicolaus Otto developed automobiles powered by internal-combustion engines. The automobile revolutionized industry and daily life in the United States, as well as elsewhere. In the 1920s, American automakers used assembly line techniques pioneered by Henry Ford to bring the car within reach of middle-class families. The introduction of the car caused an explosion of development in related industries and services such as oil refineries, rubber factories, and auto parts stores.