How much of center city resident poverty is caused by physical distance from suburban jobs? The “spatial mismatch hypothesis” posits that the answer is “a lot”. The core story is that the urban center city poor are poor because they can’t easily commute to suburban jobs. Free cars might solve this problem! Glaeser and I discuss job sprawl in this paper. My colleague Michael Stoll (and my friend Steve Raphael) have written about the social benefits of increasing access to cars for the urban poor. In today’s NY Times, Paul Krugman endorses the key role for the spatial mismatch theory. John Kain, the great late Harvard economist, wrote the best early paper on this subject and revisited the topic in this 1992 paper. John Quigley, my co-author and good friend who died in 2012, wrote one of the better natural experiment papers using the BART expansion to test for the impact of spatial mismatch.
Now for policy wonks, the spatial mismatch hypothesis is an attractive idea because it suggests that through improving urban travel speeds that economic opportunity will increase. The true test of this optimistic hypothesis would be to take center city residents and randomly choose a subset to live closer to suburban jobs and then to later test whether this “treated” group is now more likely to be employed and earning higher wages relative to the “stranded” control group. Such a field experiment has been slightly tried with the MTO experiments and unfortunately the answer appears to be “no”. Take a look at this.