A streetcar suburb is a residential community whose growth and development was strongly shaped by the use of streetcar lines as a primary means of transportation. Such suburbs developed in the United States in the years before the automobile, when the introduction of the electric trolley or streetcar allowed the nation’s burgeoning middle class to move beyond the central city’s borders. Early suburbs were served by horsecars, but by the late 19th century cable cars and electric streetcars, or trams, were used, allowing residences to be built farther away from the urban core of a city. Streetcar suburbs, usually called additions or extensions at the time, were the forerunner of today's suburbs in the United States and Canada. Western Addition in San Francisco is one of the best examples of streetcar suburbs before westward and southward expansion occurred.