Power transformer station in South Carolina. (Corbis-Bettmann)

Transportation is energy in motion. Transportation, in a fundamental sense, is the application of energy to move goods and people over geographic distances. Freight transportation may be regarded as part of complex logistical and/or distribution systems that carry needed materials to production facilities and finished goods to customers. Transportation of passengers can serve long-distance travelers, daily commuters, and vacationers, among others. Special systems accommodate the requirements people have for mobility throughout the day. A wide variety of specific technologies and management systems are involved, and from the mid-nineteenth century, a large portion of the world's energy supply has been devoted to transportation.

When sailing vessels predominated at sea and when horses or draft animals provided basic land transport, energy demands by transport systems were small. With the advent of increasingly...