In the agricultural age, the 18th and 19th century, the American Dream could have been summarized as “40 acres and a mule.” An independent Jeffersonian “yeoman farmer” was an ideal that attracted many immigrants here. In the industrial age, the early and mid-20th century, the American Dream could have been summarized as “a single family house in the suburbs with a white picket fence around it,” what I call drivable sub-urban. That industrial age was predicated upon steel manufacturing, automobile manufacturing, marketing and maintenance, auto finance and insurance, road-building, tire manufacturing and marketing, finding, processing and distributing petroleum and all the great drive-in possibilities that unfolded. As you “saw the USA in your Chevrolet,” you were making yourself wealthier. Today’s knowledge-based economy is “driving” yet another redefinition of the American Dream as it plays itself out on the ground. This new version is based upon choice; choice of living as either a rural gentleman farmer, in suburban splendor or in a vibrant walkable urban place... or all three depending upon time of life and financial resources. However, there is a severe supply shortage of the walkable urban version, which has driven up prices, gentrified urban neighborhoods and called upon the real estate development industry to build something they know very little about. And there is a supply glut of suburban single family homes. It will take a generation for the pent-up demand for walkable urban development to be satisfied and the drivable sub-urban glut to be worked out, converted to rentals or bulldozed. Related: "Is America's suburban dream collapsing into a nightmare?": CNN.com ------- Christopher B. Leinberger is a land use strategist, developer, teacher, consultant and author, helping to make progressive development profitable. He is currently a Visiting Fellow at the Brookings Institution in Washington, D.C. He is the author of The Option of Urbanism: Investing in a New American Dream from Island Press.