Posted by: Josh Lehner | December 8, 2014

Vehicle Miles Traveled, Age Edition

Our office oversees the state’s Highway Cost Allocation Study each biennium and one of the topics discussed, obviously, is the issue of vehicle miles traveled. Nationally VMT is effectively flat, while VMT per capita is down. In Oregon we’ve seen similar, yet more pronounced, trends. One contributor to this decline is the fact that younger individuals are not driving to the same degree as previous generations. In fact they’re not even getting driver’s licenses to the same degree either. There are a number of pet theories out there as to why (cost of driving or insurance, connecting with friends online instead of cruising, etc) but regardless of the exact reason(s), it’s a fact. So it was a surprise this morning to see a new report from City Lab titled It Turns Out That Millennials Do Drive. Well, yes, of course they drive. But I think the thrust of the argument largely misses the mark. The report shows that the share of Millennials that commute to work by car/carpool is largely the same, albeit down somewhat in a few metros. However the real story for the transportation system isn’t necessarily the mode of transportation, but the usage of the system. In particular VMT and VMT per capita. For a rough cut, I am using the National Household Travel Survey data. As shown below, the trends are clear. The percentages listed are the changes from 1995 to 2009. Even if the share of folks driving to work is largely the same — it is, if you look at the Census and ACS data — the amount of driving is way down, which is the real story here. It has big implications for things like the gas tax, which is not raising the amount of revenue needed to keep up with infrastructure replacement/repair costs.



  1. Is this really an apples to apples comparison? 1995 and 2001 were relatively prosperous years, while 2009 was in the middle of the Great Recession. It might also be that the relative price to earnings ratio of gasoline was higher in 2009, which has a known effect of lowering miles traveled. Combine the effects of lower incomes with higher gas prices and you might account for much of the variance.

    • Hi Tom. Thanks for the comment. Sure, I think the economy and gas prices are influences to some degree. However, they can’t explain it all. If you look at the national VMT back to the 70s or the link I provide above that includes Oregon, we’ve gone through business cycles and oil shocks and the like. There is a clear, fundamental break in VMT and VMT per capita that is not just related to the Great Recession. National VMT flattened out in 2005 and in Oregon it was the late 1990s. These are longer-run, societal trends and changes. It’s taken awhile for folks, us included, to wrap our heads around this.

  2. I wonder what the charts would look like if you included virtual miles driven such as in “Mario Cart” and “Grand Theft Auto”?

    • Ha! I think VMT per capita would show nearly exponential growth in the early 2000s with GTA. Not that I know anything about that from my college days…

  3. Josh, are there good data sets available that would allow someone to test the hypothesis that vehicle miles traveled are a function of the number of lane-miles available? The idea of induced demand seems persuasive, but I would love to see it in the data.

    • Hi Doug. Hmm, not exactly sure where you can pull this data. However, based on the conversations I’ve had and reading some of the literature, it appears to be the clear consensus that it’s true. Increase capacity and it gets filled. Some due to switching over from smaller streets, or switching from mass transit to car, or whatnot. However, increasing capacity is at least correlated with increasing driving. I’m not a transportation economist however, but this is my reading of the topic.

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