A Chicago Tribune editorial concerned with multiple years of construction on the Kennedy Expressway in Chicago ends with a claim that the traffic issues bolstered suburban businesses:

Kennedy problems, or at least the perception thereof, certainly helped bolster a lot of the growth this past couple of years in suburban business districts like those in the likes of Naperville, Glencoe, Wheaton and Aurora, as suburbanites and exurbanites looked beyond Chicago to avoid the Kennedy at all costs.

Good for those suburbs for jumping on an opportunity. But Chicago got a “lanes closed, expect delays” warning for years — a handicap it most certainly did not need.

How might we know that this construction on a highway leading northwest out of Chicago boosted business in suburban areas (including several that are different directions from the Kennedy)? Some possibilities:

1. A rise in the number of visitors or patrons in these suburban businesses and a decline in visitors or patrons in Chicago. These might not be causing each other but trends going different directions might be taken as evidence for this argument.
2. Survey or interview data that suggests suburbanites factor in traffic in Chicago when making decisions about where to go. It might go something like this: “The drive into Chicago just takes too long…let’s go somewhere that is closer and easier to get to.” Anecdotal evidence might point in this direction but how often does this happen?
3. Changes in commuter patterns and/or the presence of entertainment and business centers in the suburbs. As metropolitan areas have expanded, how many people find jobs, shopping, and cultural opportunities in other suburbs rather than in the big city? (This has happened already in American metropolitan regions but some Chicagoland specific data would be interesting.)
4. Evidence of direct efforts from suburban communities or businesses to attract people by referencing the issues present in going to Chicago. For example, do any suburban downtowns tell people they do not need to go to Chicago to find X? Or do businesses make this argument? Or suburban shopping malls?