Is the Decline in U.S. Driving a Statistical Artifact?

Wendell Cox has a very informative post over at (12/31/2011) discussing recent trends in driving (based on vehicle miles travelled). Wendell notes:

“The latest figures from the United States Department of Transportation indicate that driving volumes remain depressed. In the 12 months ended in September 2011, driving was 1.1 percent below the same period five years ago. Since 2006, the year that employment peaked, driving has remained fairly steady, rising in two years (the peak was 2007) and falling in three years. At the same time, the population has grown by approximately four percent. As a result, the driving per household has fallen by approximately five percent.”

Some commentors have suggested this reflects a fundamental change in household preferences, but this is unlikely. The U.S. represents a mature travel market, and with automobiles penetrating the market so deeply, it’s unlikely this mode could make much more headway in terms of market share. So, the apparent “plateauing” or decline in driving is more statistical artifact than fundamental change.

Wendell discusses a number of factors that have contributed to the decline of travel, and I won’t go into them here (he outlines 10 factors so read the post!), but analysts should be careful to avoid

  • comparing travel changes during a period of rapid growth with periods of slow growth because recessions result in temporary reductions in income but long-term travel trends are determined by long-term, or permanent, changes in income;
  • comparing travel choices during low-mobility and low-income stages of economic growth to travel choices and behavior once economies have matured with high-income and high-wealth households.

Moreover, as Wendell notes, the decline in driving has not translated into an equivalent increase in alternative modes. Transit is up, but not by as much as autombile travel is down. Thus, the decline represents a reduction in travel overall, not a fundamental shift in travel preferences. The key will be to look at travel behavior and changes once the economy is growing again.