Slow Down to Save Gas: Fuel Economy Decreases ~27% When at 80 mph vs. 60 mph

The Office of Energy Efficiency & Renewable Energy is back again with some fun facts about fuel economy. This week, studies showed that speeding up 20 mpg used 27% more gas. How do drivers get better gas mileage from any car, truck, or SUV?

“Slow down to save gas” is the best tip for better fuel economy

"Slow down to save gas" is the best tip for better fuel economy
A fuel pump is seen at a gas station | Sven Hoppe/picture alliance via Getty Images

The Office of Energy Efficiency & Renewable Energy fact of the week showed the advantages of slowing down on the road. The U.S. Department of Energy experiment involved driving various cars at different speeds to see how speeding impacted the fuel economy. Using a light-duty vehicle going 80 mph, the fuel economy was 27% lower than when that same vehicle was traveling at 60 mph. That means you are getting way less out of a tank of gas!

The study showed that the most fuel-efficient speed was somewhere between 40 mph and 50 mph for light-duty vehicles. This applies to cars and light trucks, but the Oak Ridge National Laboratory studied 74 different vehicles to get this number. “The best fuel economy is typically obtained when the vehicle is traveling at the lowest speed in the vehicle’s highest gear,” the study noted.

Office of Energy Efficiency & Renewable Energy says to slow down to save gas

fuel economy
Fuel economy graph for light-duty vehicles | Office of Energy Efficiency & Renewable Energy

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The 74 light-duty vehicles used in this study included two-seaters, sedans, wagons, sport utility vehicles, pickup trucks, and even minivans. The 2003-2012 vehicles had both manual and continuously variable transmissions. Four-cylinder, six-cylinder, and eight-cylinder engines, too. The U.S. Department of Energy included vehicles with two-wheel drive and four-wheel drive.

That graph shows that vehicles going 40 mph were getting an average of 32 to 33 miles per gallon, which decreased a bit at 50 mph. The average mile per gallon at 60 mph was between 25 and 30 mph. Driving 80 mph saw the average miles per gallon go down to 20 mpg at that speed.

Drive sensibly, and you might have to fill up less

The U.S. Department of Energy has more helpful tips for drivers, such as driving more efficiently. Aggressive driving, such as speeding, rapid acceleration, and braking, is a great way to waste gas. This study showed that speeding on the highway can lower fuel economy by 15% up to 30%. In stop-and-go traffic, that number changes to anywhere from a 10% to 40% loss of gas mileage.

“Sensible driving is also safer for you and others, so you may save more than gas money,” the government says. You can also consider getting a more fuel-efficient car.

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