As cities grew more crowded, and often more impoverished and costly, more and more people began to migrate back out of them. But instead of returning to rural small towns (like they’d resided in before moving to the city), these people needed close access to the cities for their jobs. In the 1850s, as the urban population greatly expanded and transportation options improved, suburbs developed. Suburbs are the communities surrounding cities, typically close enough for a daily commute in, but far enough away to allow for more space than city living affords. The bucolic suburban landscape of the early twentieth century has largely disappeared due to sprawl. Suburban sprawl contributes to traffic congestion, which in turn contributes to commuting time. And commuting times and distances have continued to increase as new suburbs developed farther and farther from city centers. Simultaneously, this dynamic contributed to an exponential increase in natural resource use, like petroleum, which sequentially increased pollution in the form of carbon emissions.
As the suburbs became more crowded and lost their charm, those who could afford it turned to the exurbs, communities that exist outside the ring of suburbs and are typically populated by even wealthier families who want more space and have the resources to lengthen their commute. Together, the suburbs, exurbs, and metropolitan areas all combine to form a metropolis. New York was the first U.S. megalopolis, a huge urban corridor encompassing multiple cities and their surrounding suburbs. These metropolises use vast quantities of natural resources and are a growing part of the U.S. landscape.