January 31, 2014

The U.S. Department of Transportation Consistently Overestimates How Much We Will Drive

The Washington Post recently reported that, for the past decade, the U.S. Department of Transportation (DOT) has consistently overestimated future growth in vehicle-miles traveled (VMT) in its biennial Conditions and Performance Report to Congress. The Post cites a study conducted by the State Smart Transportation Initiative that compared the DOT’s 20-year projections of VMT to actual VMT. In every report since 1999, the DOT has predicted a sharp increase in VMT, though in reality VMT growth slowed and seemed to peak in 2007. The 2007 peak could be a “blip” and VMT may increase as the economy improves. But if it is not a blip, these overestimations could have a real effect on planning decisions, indicating a need for road capacity or infrastructure that does not exist.

Though the DOT generates the report, they do not come up with the figures on their own. Instead, they aggregate forecasts given to them by state and local agencies that seem, according to the Post, to “assume it’s still 1980 and driving is going to increase sharply for the foreseeable future.” The article notes that, although it’s not surprising that no one predicted this trend initially, it is surprising that forecasts have not caught up. The DOT’s 2012 report is due soon and may show that transportation estimates are adapting to reality. If not, examining these estimations could be important for future decision making.