The yellow arrow represents the passage of time, the horizontal axis represents fuel economy (increasing for the first 12 years) and the vertical axis represents horsepower (on the rise since the late 1980s). (The chart was derived from this very large powerpoint presentation (PPT) by Cambridge Systematics.)

The numbers show that, as of 1975, the average new passenger vehicle burned 7.6 gallons of gas for every 100 miles driven. By 1987, that had fallen to 4.5 gallons -- meaning that new cars used about 40 percent less gas than they did 12 years earlier.

By any measure, a 40 percent decline in gas consumption in just 12 years is quite an accomplishment!

The fuel savings were the result of two simultaneous trends: the average car got lighter, and engineers tuned new car engines for efficiency rather than power and acceleration. In short, the auto industry -- from boardroom to design shop to factory floor -- focused its efforts on squeezing more miles out of less gasoline.

But in the mid-1980s, oil prices fell, the economy picked up, and federal fuel-economy standards topped out. So car manufacturers switched gears, pouring their technological advances into increased vehicle weight and horsepower. As a result, automotive engineers spent most of their time trying to squeeze as much torque and acceleration out of their engines as possible. Efficiency gains stalled at first; and then later, with the rise of SUVs and other light trucks, fleet-wide fuel economy actually went into reverse.

Fortunately, since 2004 -- when fuel prices started to rise in earnest -- we've notched some modest improvements in fuel economy. Yet preliminary data for the 2007 model year (PDF) suggest that those improvements may have hit yet another road block, with an incremental gain in horsepower but no improvements in fuel efficiency. Sigh.

I know, I know, I'm running the risk of sounding like a chiding schoolmarm, tut-tutting over Americans' collective shortsightedness in choosing muscle over efficiency.

But I'm trying to make a different point altogether: given the right conditions, technological change can be incredibly rapid. We forget this all the time, and fall into the trap of believing that the way things are right now is how they'll always be. But a simple change in policy (or a steeper change in prices or economic conditions) can foster rapid changes in our appetites and behaviors.

That's exactly what happened in the late 1970s and early 1980s: we hit a crisis, Congress passed some new standards, and quite quickly the automotive industry reinvented itself, ratcheting up fuel economy at a pace many people thought would be impossible. Even the last few decades of fuel economy stagnation have hidden remarkable change: automotive engineers have squeezed ever more horsepower out from under the hood, with little overall change in fuel efficiency.

So to anyone who says that fuel consumption is a given -- that big automakers are simply unable to respond to new incentives or meet tougher fuel economy standards, or that consumers simply can't alter their vehicle preferences -- I say: take a look at our history. Change isn't just an abstract or theoretical possibility. It's what we've been living with, well, for as long as any of us can remember.

(Photo by Telstar Logistics, distributed under a Creative Commons license.)