It may not be the most practical solution, but driving less generally seems like one of the most straightforward ways to save fuel.

Now, two recent studies show that it sometimes isn't that simple.

On the one hand, Americans are driving more. On the other, they are using less fuel while doing it.

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The first study, released by the U.S. Department of Transportation (DoT), shows that annual vehicle-miles traveled (VMT) surged in recent years.

That recovery in miles traveled has largely tracked the recovery from the Great Recession of 2008 through 2011, during which VMT plummeted.

The DoT data showed that Americans drove just over 3 trillion miles in 2014, the second-highest total recorded in 79 years of data collection. It was only exceeded by the total for 2007.

Traffic in Atlanta, Georgia during rush hour (via Wikimedia)

Traffic in Atlanta, Georgia during rush hour (via Wikimedia)

This bucks the trend of several studies over the past couple of years, which had indicated that annual VMT was in a possibly-permanent decline.

Yet this latest study indicates that the opposite may be happening.

U.S. drivers covered more miles in December 2014 than any month last year. December 2014 was actually the most-traveled December on record since 1939, the earliest year with available data.

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While Americans appear to be driving more, a second study claims they are using less fuel.

The University of Michigan Transportation Research Institute (UMTRI) tracks car ownership and fuel consumption, and found both to be at their lowest levels in years.

In 2013 (the most recent year with available data), each U.S. vehicle consumed an average 524 gallons of gasoline, compared to 602 gallons in 1984, the year the UMTRI began keeping records.

Traffic at the I-10 & I-405 interchange in Los Angeles, California (by Mario Roberto Duran Ortiz)

Traffic at the I-10 & I-405 interchange in Los Angeles, California (by Mario Roberto Duran Ortiz)

Gasoline consumption per household was also down, from 1,106 gallons in 1984 to 1,011 gallons in 2013. That's 19 percent less than in 2004, the peak year for gasoline consumption.

Breaking down the numbers to gasoline consumption per person, researchers noted a decrease from 400 gallons in 1984 to 392 gallons in 2013--down 17 percent from the 2004 peak.

Overall, despite population growth of 8 percent, U.S. gasoline consumption fell 11 percent between 2004 and 2013, said the UMTRI's Michael Sivak.

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He also noted that there are fewer cars per person and per household than at any point in the last two decades.

Of course, fewer cars doesn't automatically lead to a decrease in overall miles traveled.

While urbanization and telecommuting would seem to lessen the need for commuting by car, a recent Brookings Institute study found that jobs are actually moving further away from people.

New York City traffic at night, by Flickr user paulobar

New York City traffic at night, by Flickr user paulobar

Even in the face of increase car usage, it's worth noting that fuel consumption will continue to decrease as older models are replaced with more efficient new ones.

Federal Corporate Average Fuel Economy (CAFE) standards require carmakers to achieve fleet average of 54.5 mpg by 2025--equivalent to 42 mpg on the window sticker.

That means any given new model is likely to be at least a little more fuel efficient than its predecessor over the next decade.


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