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The “Diet Soda Effect” on Buying a Second Car

By: Kristi Kenyon October 30, 2017
A new study finds families who buy a fuel-sipping car are likely to own a gas guzzler as their second vehicle.

Have you ever rewarded yourself after a long run with a few gluten-free donuts? Or maybe followed up a hard workout with a skim-milk, sugar-free latte (or two)?

If so, you’ve fallen prey to the “Diet Soda Effect:” a term used to describe people who order reduced fat/sugar snacks in order to justify the increased consumption of otherwise unhealthy food. A recent study conducted by economists at the University of California, Davis (UC Davis) suggests that this type of behavior has now translated to the automotive market.

The study, released in late September, shows that families who own fuel-efficient cars tend to buy big, powerful gas guzzlers as their second vehicle, justifying the purchase by touting their environmentally-friendly EV or hybrid—while essentially neutralizing the positive effects of that vehicle. Additionally, the research found many families use their fuel-efficient vehicle for daily commutes, while using their gas-guzzler for activities that need more room or horsepower (such as hauling equipment or taking a road trip). These habits reduce their future gas savings by up to 60%.

So why do families practice these inefficient habits? One reported reason: many don’t find the fuel-efficient cars to be easy to use outside of the city.

“It’s hard to be a two-electric-car household. There is still that range anxiety issue,” said Hugh Byrne, a San Francisco marketing and data executive, describing the fear that an electric vehicle won’t make it to its destination—or a charging station—on its current charge, leaving drivers stranded.

Byrne also highlighted another concern: comfort. While small electric cars are great in the city, they’re typically not very comfortable on longer rides—especially when it’s windy.

While a change in consumer habits is paramount, the study’s authors also called into question the feasibility of current emissions and conservation policies nationwide, and whether they should be adapted to human behavior until that behavior gradually changes. 

“On average, fuel economy standards are putting more fuel-efficient cars in households,” said David Rapson, associate professor of economics at UC Davis and lead author of the study. “But if it causes people to buy a bigger, less fuel-efficient second car to compensate, this unintended effect will erode the intended goals of the policy.”

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