SSTI: Travel Demand Estimates Overshooting Reality

In a recent post from the State Smart Transportation Initiative, a group that promotes environmental sustainability and economic equity within transportation policy, says USDOT continues to overestimate the amount of demand on the transportation infrastructure in its most recent Conditions and Performance report.  

The chart from SSTI below, shows the trends identified in previous C&P reports, including the 2013(trend) line, which is new to this report.  The solid lines estimate growth at approximately 1.86%, and are based off of FHWA's HPMS program.  The new line is based off of observed trends rather than HPMS program, and shows growth at 1.36%.

However as SSTI's Eric Sundquist writes:

The three years since 2010 have all seen much lower growth than either estimate would suggest, -0.7 percent, 0.3 percent, and 0.6 percent respectively. So by 2013, the year the new report is dated, the new C&P was already estimating VMT that was 5 to 6 percent higher than actual, depending on which of the assumptions is used.

Both the C&P report and the SSTI illustrate the complex nature of projecting travel demand and the assumptions used in models.  Traditional transportation model were designed to assess the utility and need for highway and roadway expansion.  However, changing preferences, tight budgets, and technology are changing the demands on the system in ways these models cannot account for.  

Fortunately, any slowing in VMT growth allows local and state agencies to focus on pavement preservation rather than capacity expansion.  For more information, check out

Original post from SSTI

FHWA's Conditions and Performance Report