Comparing the Official DOT forecasts of road traffic with actual road traffic.
and more here:
"[...] the US Department of Transportation has been making the virtually identical vehicle travel forecasts for well over a decade. All of those forecasts project rapid and incessant growth in vehicle travel for as far as the eye can see. Meanwhile, actual traffic volumes have flattened out, and may actually be falling."
"That overestimate is the equivalent of adding travel from five average-sized states to the total. And the overestimate came in the year of the release, not year 20. This is troubling in a report that is widely regarded as a gauge of the “need” for funding new highway capacity."