Monday, May 30, 2011

How many calories in a gallon of gas?


Let's talk about calories. Calories are units of energy. One calorie is the approximate energy required to heat one gram of water by 1° Celcius. All of us are familiar with calorie counts on the back of food packages. Food calories are actually kilocalories, or one thousand "gram calories". We'll refer to food calories as "calories" for the sake of simplicity.

The Mayo Clinic calorie calculator recommends that an active 30 year old man at six-feet tall and 180 pounds consume about 2750 calories per day. An apple contains about 95 calories. Eight ounces of freshly squeezed orange juice contains 110 calories. A slice of wheat bread has about 90 calories, a loaf 1620 calories. A slice of Papa John's pepperoni pizza is 340 calories, a whole pie 2800 calories. A Big Mac is about 560 calories. A Chipotle burrito with carnitas, rice, pinto beans, cheese and sour cream comes out to around 950 calories. A whole roasted chicken is about 2350 calories. (See the USDA Nutrient Data Laboratory and food packages at your local grocery store for similar figures).

Although we don't eat gasoline, we can measure its caloric content, since we learned above that a calorie is merely a unit of energy. According to the internet-at-large, a gallon of gasoline contains about 30,000 calories. This means that a car getting 30 miles per gallon is burning about 1,000 calories per mile. A car that is only averaging about 15 miles per gallon is burning closer to 2,000 calories per mile. In contrast, an average man burns about 100 calories when walking a mile, 125 calories when running a mile. That same man burns about 40 calories per mile while biking at 15 miles per hour.

Driving a midsized car throughout the city at 15 miles per gallon is therefore 1/20th as energy efficient as walking through the same city. Stated conversely, walking is 20 times as energy-efficient as driving around a city. Bicycling around the city is 50 times as energy-efficient as driving!

It is a wonder then, that people tend not to scrutinize their driving decisions as scrupulously as their eating decisions. The reason probably has more to do with habit and blissful ignorance than anything else. We are comfortable with our cars. Gasoline is affordable. Driving a couple blocks to pick up a carton of milk is not a big deal. Who cares how many calories we're burning? It's not like we could feed hungry people with the unused gasoline.

Many Americans don't even have the choice to bike or walk for quick errands. They live in "food deserts" -- places where whole foods aren't available within a reasonable walking/biking distance. Not a huge problem for those wealthy enough to own cars who choose to live in the quietude of suburbia, but what about poor folks who can't afford to own a car or move to a more liveable area?

There are at least two morals to this story. First, as individuals we should think carefully about our actions and their place in the global order. Is it worth the five minutes saved to run a one-mile errand by car rather than by bicycle or foot? Could there be something inherently good and empowering about walking or biking as a means of transportation (rather than for leisure)? Does prioritizing "human" modes of transportation have other beneficial side effects, such as more equal access to whole foods, safer streets, and reduced obesity?

Second, municipal governments should promote (or better yet, require) smart urban design: where uses of land are not so discrete and separate that one cannot comfortably walk to the store for a quart of milk or an apple or a loaf of bread; where roads are not so wide that they cannot be safely crossed by a slow child or an aging grandfather; where people, regular old people who aren't athletes or daredevils or seasoned urbanites, can ride a bicycle down the street without fear of serious bodily harm. The time is now for individuals and governments to concern themselves with calories consumed at the pump, just as they do with calories consumed on the plate.


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