Junk in the Trunk

The journal Engineering Economist calculates that compared to 1960, the weight of today’s obese Americans has caused a 1 billion-gallon increase in gasoline usage from hauling around all the extra weight over the past 46 years. The conclusion: if we just ate less we could end dependence on foreign oil.

Apples and oranges ought to be protesting this finding!

Aside from the law of conservation of energy, which this blog does not pretend to fully understand, the flaws in this analysis are numerous and obvious.

First of all, nothing is the same now as in 1960 (with the exception of Elvis’ popularity). The cars back then were far less energy-efficient than they are today and the gasoline is better quality and at the same inflation-adjusted price. There are more people today, not only due to the baby boom but due to safer cars killing fewer people.

And if all that weight resides in the passenger compartment of our cars as a result of eating too much junk, then it is logical to assume less gasoline is being used for turnip trucks.

Blaming excessive gasoline usage on junk food is like blaming global warming on your faulty toaster. The authors have it entirely backwards. We are not spending more on gasoline because we are fat, we are fat because we are spending more to drive places we used to walk.

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5 thoughts on “Junk in the Trunk”

  1. I’m not going to pretend that I read the article, because I didn’t, but I am confused by how this claim can even be considered valid. It’s true that gross vehicle weight is a concern for engineers and designers when they are striving for efficiency, but the weight of a human is a very small percent of your total weight.

    The NHTSA lists the 2-door 2005 Pontiac Sunfire with a curb weight of 2,594 lbs. That’s a pretty small and relatively popular vehicle, however even for it an obese American male would add less than 10% to the gross vehicle weight. When you get up into larger, more substantial vehicles that percentage gets even smaller.

    a 20% increase in gross vehicle weight (assuming two obese adults) is not going to increase the rolling coefficient of friction to the point that it will even make up for, let alone exceed, the efficiency gains made by using modern fuel in a modern engine. We’re not talking racing here where even an extra pound can throw off your times, this is general every-day driving.

  2. I’m afraid I don’t quite understand your argument.

    Yes, many variables have changed in the last forty years — engine efficiency, commuting distance, and population being obviously relevant ones.

    However, gross vehicle weight is one that is both relevant, easily to isolate, and comparable over time. Discussions about producing more fuel-efficient cars always identify vehicle weight as one of the most important factors, simply because cars spend a huge portion of their fuel overcoming inertia. This means that studying how passenger weight effects gas milage is, in fact, entirely valid.

    Furthermore, end-to-end analyses of energy consumption suggest that petroleum-fueled cars are far less efficient than food-powered people on foot. So “conservation of energy” does not invalidate this comparison.

    Your post is full of clever quips, but is mostly poor reasoning poorly argued. The exception is the last sentence, which is quite insightful. When a person transitions from walking to driving, it creates a potential double hit on their pocketbook and environment: first by using a less efficient method for traveling the same distance, and second by further decreasing the efficiency of that method. The benefit of replacing just a small portion of driving with walking could disproportionately large.

    So a better way would to put it would be: “We are not only spending more on gasoline because we are fat, but we are becoming fatter because we are spending more to drive places we used to walk.”


  3. Congradulations. You’ve won the award for inane babbling.

    None of the points you bring up actually counter the research. The research is very simple to verify, and pretty good on face value. All other factors equal, if people weigh more we use more gas. This research just puts a number to that patent truth.

    Perhaps if Mr. Allen could compose more than a 15 minute rant, his articles would be of a little more use to this blog.

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