What does "urban sprawl" primarily refer to?

Urban sprawl primarily refers to the uncontrolled expansion of urban areas into rural land. This phenomenon often occurs when cities grow outward, consuming surrounding rural areas, and typically results from factors like population growth, increased automobile use, and the desire for larger residential spaces. This expansion can lead to various social and environmental issues, such as increased traffic congestion, loss of agricultural land, and challenges in providing public services.

In contrast, the other options do not accurately describe urban sprawl. The growth of rural areas into urban spaces suggests a reversal of the typical sprawl phenomenon and does not capture the essence of urban expansion. The controlled development of urban regions implies regulation and management, which contradicts the idea of sprawl being uncontrolled. Lastly, the development of urban areas only along highways describes a specific pattern of growth, often termed corridor development or strip development, but does not encompass the broader concept of urban sprawl. Therefore, the definition emphasizing uncontrolled expansion into rural land is what makes it the correct answer.