Just about one year ago, Rob Puentes and I published a white paper entitled ‘The Road… Less Traveled.’ As the title suggests, our research found that Americans as a whole were driving less from December 2007 onwards--and we were in the midst of the largest sustained drop in driving in American history. Moreover, we found these drops were largest when viewed on a per capita basis, proving that individual behavior change may be afoot.

 The implications of these sustained drops can’t be understated. On the positive side, less VMT quite literally means reduced emissions, which is great news for the environment. It may also be a signal of the market’s increased interest in denser, mixed-use development, whether in classic urban cores or sprouting suburban ‘town centers,’ that require fewer and shorter car trips.

Conversely, falling VMT is a big problem for transportation funding. Since the gas tax is the primary source of federal and state transportation revenue, falling VMT means less money for needed investments. In fact, these drops combined with rising outlays cause a serious trust fund shortfall--one which has been addressed through general fund infusion in both 2008 and 2009.

So where are we now, almost exactly a year later? Well, national VMT has increased for four consecutive months from May to September. Based on historic patterns, such an increase in driving should lead to an increase in trust fund revenues through more gas tax receipts.

However, the four-month increase of 18 billion miles pales in comparison to the 76 billion mile drop from our national peak in August 2007. Clearly, the nation’s surface transportation funding crisis will continue as long as the gas tax rate holds constant and VMT doesn’t dramatically rebound.

From a funding perspective, the more significant news is the per-capita VMT numbers. In the midst of that 76 billion mile drop from the national peak, the country also added another 6 million people according to estimated Census population growth rates. As shown in the chart below, this means the country continued its historic drop in driving per person. At this point VMT per capita in September 2009 is equal to the personal miles driven in January 1998.

To put that decade plus consistency in perspective, it was a time when we had two years left on President Clinton’s second term, no formal wars abroad, and a real national GDP 22.2 percent less than where we stand now.

While it’s easy to rest blame on the Great Recession--and it certainly is a part--there is more going on here than just recent drops in economic activity. Centralizing development in cities and suburbs, stabilizing social trends, and the myriad of unique local effects all aggregate within these national trends. And as long as these trends continue, whether a further drop in per capita VMT or just an extended plateau, the country will have less money to address its evolving transportation needs.

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