No matter how old you are, it’s a safe bet that for most of your lifetime traffic has been growing. Total US vehicle miles traveled (VMT) has doubled and doubled again, rising like an ocean tide since the invention of the automobile, reaching about 3 trillion (!) annual auto miles in the USA. The escalation of auto traffic has been a constant for so long, it's colored the blood of policymakers. Growth is a given.
|[Death, taxes, and rising VMT...]|
|[Per capita VMT trends.]|
The are a few theories for this decline, beyond basic economic reflexes. You could point to demographics, culture, or peak oil. One one hand, it doesn't seem like that big a deal. The US is still leading the world in auto dependency. We still drive almost 3 trillion miles each year in our 280 million cars.
On the other hand, this new trend is a big deal for how we perform transportation modelling. This shifting tide means that cities and states don't have to project infinite growth into the future any more. Things have changed. As the US DOT puts it, “the United States has reached a critical juncture in terms of national mobility trends and underlying socio-demographic conditions and travel behavior that will result in more moderate rates of annual vehicle miles of travel (VMT).” (Rather inelegant, that.)
Should Our Cities Be Extrapolating Growth?
|[ADTs from St Paul's 2008 Comprehensive Plan. (2030 projections in parentheses.)]|
One of the exciting things about peak VMT is that the city typically will project ADT counts for 2030 alongside current counts. For example, Summit Avenue currently has 12,400 cars per day, but in 2030 it's projected to have more than 15,000. Or Lexington Parkway is projected to grow from twenty-two thousand to over twenty-six thousand cars per day. MNDOT, Hennepin County, and Minneapolis each have similar projections. These projections are standard practice in public works and transportation departments across the country.
|[At this point, our cities can choose their own adventure.]|
Taking this step would liberate our cities from the regime of increasing traffic. Getting rid of the assumption of increase could free our vision, and make room for more ideas about street design or mode choice. Instead of fatalistically designing roads for gridlock, we could begin designing roads that meet our shared goals, things like walkability, encouraging local businesses, and encouraging sustainable energy use. In other words, we could plan for what we want to happen, not what we know is going to happen whether we like it or not.
Peak VMT is the sign that the tide has turned on car country. The monster at the end of the book isn't real. Our cities can start to relax.
PS. On second thought, maybe the decade's VMT trend is just a repeat of the 70s. So the Germans would have us believe...
Update: I shouldn't pick on Saint Paul. Their comprehensive plan has this to say about VMT trends:
Meanwhile, total Vehicle Miles Traveled (VMT) has remained flat, both in Minnesota and nationally, between 2003 and 2006 and declined 4.7% in 2007. This indicates that when considering the growth in population, VMT is actually declining.3 Additionally, in December 2007, MnDOT reduced its estimate for future VMT growth in the metropolitan area to 0.9% per year, down from an original projection of 2%.
Finally: Chuck's take on the role of projections is far more combative than mine:
I know this is difficult for many of you to get your mind around because you perceive expanding infrastructure as being a catalyst for growth, not the result of growth. And while I know I need to spend some time in a future post explaining how we transition from our current system to this new (old) approach, it all begins with that insight: infrastructure spending should never be in anticipation of growth, but only in support of places that have been successful.