People tend to blame this on oil prices, and the day may indeed come when that is a big factor, but I think it's more a consequence of 1) the attractions of density and 2) overbuilding as a direct consequence of growth mania built into the decision making system. It doesn't matter how cheap oil is; spending two hours a day in traffic jams is a huge cost I'd prefer to avoid.
Here's an Atlantic article by Christopher Leinberger that makes the case for abrupt decline of the sprawl, entitled "The Next Slum" and blurbed "The subprime crisis is just the tip of the iceberg. Fundamental changes in American life may turn today’s McMansions into tomorrow’s tenements." In a nutshell:
Arthur C. Nelson, director of the Metropolitan Institute at Virginia Tech, has looked carefully at trends in American demographics, construction, house prices, and consumer preferences. In 2006, using recent consumer research, housing supply data, and population growth rates, he modeled future demand for various types of housing. The results were bracing: Nelson forecasts a likely surplus of 22 million large-lot homes (houses built on a sixth of an acre or more) by 2025—that’s roughly 40 percent of the large-lot homes in existence today.
For 60 years, Americans have pushed steadily into the suburbs, transforming the landscape and (until recently) leaving cities behind. But today the pendulum is swinging back toward urban living, and there are many reasons to believe this swing will continue. As it does, many low-density suburbs and McMansion subdivisions, including some that are lovely and affluent today, may become what inner cities became in the 1960s and ’70s—slums characterized by poverty, crime, and decay.