“„Even families who sought the suburbs or were priced out of cities now have an economic imperative to find their way back closer to town. Transportation is the second-biggest household expense, after housing, and suburban families face a relatively greater gas burden. At the same time, distant suburbs, or exurbs, where housing growth was predicated on cheap gas, have experienced the biggest declines in home values in the past year, according to a May report by CEOs for Cities, a nonprofit group of public- and private-sector officials that seeks to promote urban areas. “The gas-price spike popped the housing bubble,” said Joe Cortright, the report’s author.