As the State Smart Transportation Initiative at the University of Wisconsin points out, 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.


Each of the rising colored lines represents a forecast from a different year.  The black line represents actual traffic trends on US roads—which never rose as quickly as the forecasters had predicted, and actually started a modest decline in 2007.

Where have we seen this sort of shape before? Well, we’ve noticed these sorts of “broken record” projections time and again here in the Northwest: on Washington’s SR-520, on greater Vancouver’s Port Mann Bridge, and even in unexpected places like forecasts of water consumption. I’m sure there are other examples. It seems to be a common shape exhibited by perpetually broken forecasts—let’s call it, with apologies to H.G. Wells, “The Shape of Things Not Actually to Come.”

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  • This isn’t entirely USDOT’s fault, though. These forecasts are a “roll-up” of forecasts made by state DOTs. The US agency just collects the forecasts and reports them to the public: garbage in, garbage out.

    But in a way, that’s even more sobering than if the fault were localized in USDOT, since it provides clear and compelling evidence that the nation’s entire transportation forecasting apparatus is completely broken. In the aggregate, all of those hard working forecasters in all of those state DOTs are just making up numbers. Worse, it appears that these traffic forecasters have had no incentive to correct their work, incorporate new information, or even ensure that their forecasts pass the laugh test.

    It’d be humorous, if the fiscal consequences weren’t so dire. Washington’s transportation debate is a case in point: existing roads are in desperate need of maintenance and transit is hurting for money, but state legislators felt that they needed a transportation package full of highway megaprojects, financed through regressive taxes, to deal with all the “new” traffic we haven’t been getting for about a decade.

    So here’s hoping that USDOT—and traffic forecasters nationwide—start producing forecasts that reflect the reality of traffic trends over the past decade. It’s high time that they stop living in the early 1990s, and start getting serious about making realistic traffic forecasts.