Sprawl is driven by low land prices and economic prosperity, not by highway expansion, as previously thought. At least, that's the conclusion of a recent study by researchers at University of Illinois-Chicago's Urban Transportation Center. The rationale: First-time buyers will often trade a convenient commute for extra square footage, and larger homes tend to be built where land is cheaper, farther from the urban core. On the flip side, study data suggest that counties where jobs are plentiful have higher land costs and, therefore, fewer home buyers.