As noted in earlier posts, my students and I discussed Bill Cronon's Nature's Metropolis this past week. One of Cronon's explanations for Chicago's extraordinary growth was its role as a distribution center: railroads had both eastern and western terminals in Chicago, and so lots of stuff got collected and moved in the city. Chicago is not the only city whose development came about in part because of transshipments; one could tell such stories about Hong Kong and Singapore as well.
Coincidentally, Nate Silver had a blog post this week where he estimates that extra post-9-11 security screening reduced air travel by 6 percent. This begs the question as to how much impediments to movement are also impeding the broader economy.
I wrote a paper a few years back that linked passenger traffic at airports to employment. The finding was that an increase of one passenger per capita per year produced a 3 percent increase in jobs. A typical large city has four boardings per year per capita, so let's run the math: -.06*4*.03 is a .72 percent reduction in jobs. The US has about 139 million jobs, so a .72 percent reduction is about a million jobs. So it is possible that impediments to travel mean we have a million fewer people working than we otherwise would.
This is very much a first cut, rough kind of number, but it does give one pause. Is what we are doing at our airports worth sacrificing a meaningful number of jobs? Perhaps. But we should still think about the trade-offs explicitly.