Looking at data from the American Community Survey, the National Housing Council finds that the median income is not keeping up with the costs of living and transportation in many U.S. cities:

Of course, incomes were falling in 2010, following the collapse of the housing market, so this data might be a little tricky to interpret. For right now, though, the clear takeaway is the basic necessities are taking up more of middle-income earners' budgets.