Ryan dug up a paper by Baum Snow that was reblogged by Matt Y. While the numbers are interesting in themselves, the swing was most dramatic to me. It wasn't just 18 percent drop with the introduction of freeways into the urban fabric but if we are to believe that city population would have increased by 8 percent that is a 26% swing in population for cities.
This is no small chunk of life and as we have seen, it was devestating to the economic vitality that cities would have maintained. As Scott Bernstein always says, urban places are the way we can build wealth. Unfortunately a whole lot of wealth was transferred and reallocated. It might be interesting to see what that 26% swing meant over time for the economics of the United States considering how much of the population lives in metro areas. We might be having different discussions today about sustainability.