Vehicle Miles Trend Assumptions Vary Between Agencies

January 2 – edited to correct Mr. Sundquist’s name.


Alexis Madrigal highlighted this 2013 post from Eric Sunderland Sundquist at the State Smart Transportation Institute in Madrigal’s Five Interesting Things newsletter.  In it, Sunderland Sundquist discusses how Vehicle Miles Traveled (VMT) trend projections are compiled by the Department of Transportation and how the assumptions behind those trends have increasingly separated from actual VMT.

A key takeaway is that the overestimates in these trends occur as soon as the year they are released.  For instance, the 2012 estimate released in 2012 (3.3 trillion miles) was found to be 11 percent too high (more than 300 billion miles off).  The 2012 estimate released in 1999 was 22 percent too high.  As these trends inform transportation planning and decision-making for all manner of state, local and federal road projects, overestimates lead to transportation spending that fails to reflect future use.  With the actual VMT trend flattening out over the last several years, to continue to have projections with rates of increase comparable to decades old-projections is completely disconnected from reality.

I thought it worth noting that the U.S. Energy Information Administration (EIA) has managed to adjust the assumptions in its VMT trend projections to reflect actual data (and continues to do so).  The EIA can be more responsive in part because it is more directly connected to the data used in its projections.  It won’t be enough for the agency to recognize changes in VMT trends; state and local entities involved in traffic data collection and trend projection must also change their assumptions.

Once the 2014 VMT data is available, it will be worth revisiting this topic.


2 thoughts on “Vehicle Miles Trend Assumptions Vary Between Agencies

  1. The name of the person at SSTI who produced the chart discussed above is Eric SUNDQUIST.

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