The first step in understanding just how much control we as individuals have over the single largest problem facing our society and our planet — fossil fuel consumption — is that we first have to understand how much energy we are using.

Lawrence Livermore Labs, in its Energy Flow Diagram of the U.S. (based on 2009 data), gets us most of the way there. Of the total 41.5 Quads used in buildings (1 Quad is equivalent to 1,050 quadrillion BTU's or 293 billion kilowatt hours of energy), individuals are responsible for 11.3 Quads.

But what about the transportation sector, which accounts for a whopping 27 Quads? How much of this can be attributed to individual passenger use? 

My marked-up version of the energy flow diagram (above) reveals a rough estimate — about 15.7 Quads are used by individuals for personal transportation. The remaining 11.3 Quads are used by business, industry and government fleets. 

This was not as easy to figure out as I thought it would be. An early release of the U.S. Department of Energy's Annual Energy Outlook (AEO) for 2011 breaks down petroleum use for transportation by type — LDV's (light-duty cars & trucks), HDV's (heavy-duty vehicles), aviation, marine and rail. Here's a pie chart of the data, but it only gives us a starting point:

To understand individual consumption, we need data on the percentage of light duty vehicle miles specifically for passenger use (versus business or government fleet use). This data, it turns out, does not exist, so some extrapolation is required. According to the EIA (Energy Information Agency), 82 percent of all LDV's were sold to consumers and the remaining 18 percent (18.1 percent of cars and 18.2 percent of trucks, to be precise) for commercial, industrial or government fleets.

It's impossible to say whether a fleet vehicle puts in, on average, more miles per year than a passenger vehicle, but considering the enormous mileage of a typical U.S. passenger vehicle — 17,000 miles per person per year — and that a good portion of fleet miles are attributable to personal use (16 percent by a recent industry study), it's a moderately safe assumption. 

Aviation presents a similar problem. There is no single study that compares jet fuel use for passenger flights versus air freight shipping. But the relative proportion of total fuel use can be extrapolated by comparing passenger kilometers traveled versus tonne-kilometers for freight on the top 10 carriers. Here I assumed a passenger weighs on average 150 pounds and is carrying 50 pounds of stuff (i.e. 11 passengers per tonne):

From that we can assume passenger flights account for significantly more fuel consumption — 68 percent compared to 32 percent for freight. And that gives us the final breakdown:

Of the total 8.2 million barrels of oil used for passenger vehicles per day, individuals directly consume 82 percent or 6.7 million barrels. And of the total 1.3 million barrels used for aviation, individuals consume 62 percent or 0.8 million barrels for a grand total of 7.5 million barrels of transportation fuel, or 58.1 percent of total transportation energy:

So in a nutshell, Americans directly consume 11.26 Quads for residential use and 15.68 Quads for personal transportation, for a grand total of 27 Quads out of 68.5 Quads or 39.4% of total energy consumed in the U.S. 

Dave Roberts over at Grist points out the gross inefficiencies built into our current energy delivery systems. A full 26 Quads of energy is completely wasted in electricity generation and distribution. But of the remaining 68.5 Quads, we directly control 27 Quads of energy. By making our homes more efficient and conserving on automotive fuel use, we could theoretically save 40 percent or more on our total energy consumption. That's 10 Quads of energy!

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