On a strictly anecdotal basis, the only instance I can think of off the top of my head where an Interstate designation purportedly contributed significantly to the establishment or expansion of commercial enterprise was the placement of the Toyota plant outside Tupelo, MS. To the best of my knowledge, the plans for that facility were finalized only after I-22 was legislatively commissioned in early 2004; the location had been one of several contenders. Whether that particular designation was the factor that put Tupelo over the finish line would be difficult to determine -- but it seems, again from anecdotal sources, that location adjacent to an Interstate route -- particularly a trunk route -- is a major factor to overseas entities facing logistic/distribution issues.
Yes, it's an "n" of 1 -- hardly robust data! Personally, I'd like to see some group assemble enough real data on this subject to perform a valid statistical study (preference: multivariant regression analysis, factoring in other enticements aside from egress). There's enough speculation -- both in this forum and within more official transportation circles -- regarding the efficacy of Interstate status to warrant a study in depth -- possibly to either validate or debunk contributory or even causal effect of I-designation and deployment. IMHO, it's long overdue!
