Another argument for carbon tax: how car buyers behave – Christopher Knittel

MIT Sloan Professor Christopher Knittel

From The Sacramento Bee

Do you rationalize splurging on your daily latte by bringing your lunch to work? Every day we make decisions like this that impact our diet and pocketbook. These same trade-offs also affect the types of cars we drive, which impacts the effectiveness of fuel-efficiency policies.

In a recent study based on five years of data from the California Department of Motor Vehicles, James Archsmith and David Rapson of University of California, Davis, Ken Gillingham of Yale University and I found that in two-car households, increasing the fuel economy of the first car encourages owners to demand less fuel economy in their second car. In other words, if you buy a Toyota Prius, you may be more likely to replace your second car with an SUV.

When households increase the fuel economy of their first car by 10 percent, they will reduce the fuel efficiency of the second vehicle by 5 percent, our analysis found. The result is that half the fuel economy gained from improving the first car is eaten away by a less fuel-efficient second car.

But that is only part of the story. It turns out that owners also ended up driving more total miles, which cuts fuel savings another 10 percentage points. In the end, 60 percent of the benefits of increasing the fuel economy of the first car disappear when the second car is replaced with a less efficient vehicle. Read More »