The car as a means of personal transportation was developed about the time of World War I, and the American city was catapulted into a radically new period, both quantitatively and qualitatively, in the further evolution of physical form and function. The size, density, and internal structure of the city were previously constrained by the limitations of the pedestrian and early mass-transit systems. Only the well to do could afford horse and carriage or a secluded villa in the countryside. Cities were relatively small and compact. They had a single clearly defined center, without any significant spatial hiatuses except where commuter railroads linked outlying towns to the largest of metropolises. Workers living beyond the immediate vicinity of their work had to locate within reach of the few horse-drawn omnibuses or the later electric street railways.
The universality of the automobile, even among the less affluent and the parallel proliferation of service facilities and highways greatly loosened and fragmented the American city, which spread over surrounding rural lands. Older, formerly autonomous towns grew swiftly. Many towns became satellites of the larger city or were absorbed. Many suburbs and subdivisions arose with single-family homes on lots larger than had been possible for the ordinary householder in the city. These communities were almost totally dependent on the highway for the flow of commuters, goods, and services, and many were located in splendid isolation, separated by tracts of farmland, brush, or forest from other such developments. Usually anchored on a cluster of shopping malls and office parks.