Ok, this is weird.  Washington’s transportation department thinks that vehicle travel is going to go up up up.  See, for example, this graph…

Total Vehicle Miles Traveled 1980 – 2030 (projected)
(Miles in billions)

The solid red line to the left represents historic traffic volumes—technically, vehicle miles travelled, or “VMT” in planner-speak.  The dashed line to the right is a prediction of future VMT growth.

But look:  there’s something awfully suspicious about these predictions.

If you close one eye and tilt your head to one side, you’ll see that the dotted line is much steeper than the solid line. In the real world, traffic growth has slowed way down in recent years, and looks like it’s on the verge of flattening out.  A closer look at the numbers (pdf link) tells the same story:  the recent slowdown in vehicle travel has been pretty remarkable. As oil prices have soared, the growth in vehicle travel has slowed; and travel per capita has actually fallen.

But the reality of rising fuel costs hasn’t sunk in to the planning department.  Instead, they’re predicting a massive, immediate increase in the growth rate of traffic, starting next year.  Yep, if you believe their predictions, traffic will grow four times faster over the next 5 years than it did over the last 5 years, at a pace 50 percent quicker than the long term average.


  • It gets worse.  Measured per driver, VMTs have been trending downward since the early 1990s. Today, it’s about the same place it was 2 decades ago. But the transportation department is predicting an immediate reversal of the recent declines, with rapid upscaling of our transportation habits—starting, once again, next year.

    Vehicle Miles Traveled per Licensed Driver
    1980 – 2030 (Projected)

    I could go on—the WashDOT is claiming anomalous growth in VMT per capita and per vehicle as well. Of course, all of these predictions could turn out to be correct.  That’s the thing about the future—you can’t know what’s going to happen until it actually happens.  But based on recent trends, both in traffic growth and oil prices, my money’s against WashDOT.

    Whoops!!  Actually, that’s not true.  My money—that is, my tax dollars—is actually being spent, right now, based on the assumption that WashDOT’s predictions are accurate.  You see, these projections aren’t just an academic exercise.  They’re being used to argue for new roads, increased traffic capacity, and all the trappings of a car-dominated transportation system.  And by building new roads to accommodate anticipated capacity, we could actually be helping to make those predictions come true.  New roads, for example, could facilitate sprawling development on the urban fringe, which in turn will make car travel even more of a necessity than it is now.

    So I’m left with 2 possibilities.  Either transportation planners haven’t caught up with the new realities of rising gas prices, growth management policies, and demographic trends that are reducing our need to drive.  Or misguided transportation investments, justified by inflated traffic projections, will create the trends that planners are anticipating.

    Either way, it looks to me as if it’s time for some new projections.