We're Driving Less, But Why? Ask Esquire!

As I’ve posted repeatedly, for almost a year-and-a-half, Americans generally, and Californians in particular, have been driving less.  This is a really big deal: there have been times where the rate of growth has been faster or slower, but there have really been only three or four instances since World War II where miles driven has actually dropped; and in those cases, not for as long as this recent decline.  Here’s the visual, from the Federal Highway Administration:

 

Now any reader of a blog on the NRDC website is going to be smart enough to posit the two most obvious theories for this decline: high gas prices and the, um, slowing economy.

Gas prices certainly impact the amount we drive, but not to the extent that would account for a decline like this.  Most people have little choice as to where and how far they drive, so gas prices are what economists call inelastic, which means that demand is pretty constant despite small price changes.  Of course, the price of anything has an impact on who’s going to buy it, but for something like gas, the long-term impacts are much more significant.  To really deal with persistently high gas prices, someone has to, say, pack up and move somewhere that doesn't require as much driving.  In the short term, people usually take the hit and make slight adjustments on relatively optional travel.

In any case, gas prices have come down (and risen) again, yet the consistent downward VMT trend continues.

The overall state of the economy, and its impact on driving, are not as well-understood as the impact of gas prices.  Nevertheless, when more than 10% of the workforce is not driving to work, you’re going to see a decline in total mileage.  In fact, a report from Inrix found that 99 out of the most congested 100 metro areas reduced congestion in 2008.  The causes: “turbulent fuel prices and a struggling economy.”

Now, clearly, I have a vested interest in discovering that actually, in fact, the reason people are driving less is because they’ve decided to take the bus, ride their bikes, hop on a train or walk to the store.  This would point to a broader cultural shift in the way we travel as opposed to just a little depression-style bump in the road on our way to more and more driving (and more and more pollution).

Which brings me to the meat of the post.  As will often happen, I found a forwarded email in my inbox directing me to an article on Vehicle Miles Travelled (VMT) trends, by Nate Silver.  It’s always fun when your nerdy subject shows up in Esquire (!), and it’s also cool when the author is the guy behind FiveThirtyEight.com, the polling site everyone who talks about polling sites talks about as being uncannily accurate and thorough.

Nate was struggling with this question, too.  How much of the VMT drop is gas prices, how much is economy and how much could be something else?  So…“To sort this out, I built a regression model that accounts for both gas prices and the unemployment rate in a given month and attempts to predict from this data how much the typical American will drive.”

While his model predicted that Americans should have driven more in January 2009, Americans actually drove 8% less. 

We don’t know why, precisely, but there does seem to be more to this decline in driving than just gas prices and an economic slowdown.  And that could indicate broader social and cultural trends towards less driving, which is great for our health and good for the planet.

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