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A recent study by Oak Ridge National Laboratory shows that the fuel economy of cars and light trucks in the study decreases rapidly at speeds above 50 miles per hour (mph). The study of 74 light vehicles included two-seaters, sedans, station wagons, sport utility vehicles, pickup trucks, and minivans for model years (MY) ranging from 2003 to 2012 with a wide variety of powertrains. Performed on dynamometers simulating highway cruising speeds on flat roads and moderate temperatures, the study results indicate that for the tested vehicles, 40-50 mph is the optimum cruising speed for high fuel economy. The average fuel economy decrease for 50 to 60 mph was 12.4%; from 60 to 70 mph the average decrease was 14%; and from 70 to 80 mph the average decrease was 15.4%. According to engineers at Oak Ridge National Laboratory, the lowest speed in the vehicle's highest gear is where the best fuel economy is typically obtained.

Average Fuel Economy by Speed, 2012 Study of 74 Vehicles
Graph showing the average fuel economy by speed registered in a 2012 study of 74 vehicles. 40-50 mph is the optimum cruising speed for high fuel economy with fuel economy decreasing as the speed increases. See table below for more detailed information.

Supporting Information

Average Fuel Economy by Speed, 2012 Study of 74 Vehicles
Vehicle Speed
(Miles per Hour)
Average of Tested Vehicles'
Fuel Economies
(Miles per Gallon)
40 33.17
50 31.86
60 27.93
70 24.12
80 20.49
Sources: U.S. Department of Energy and U.S. Environmental Protection Agency, Fuel Economy Guide.
Green Car Congress, "ORNL researchers quantify the effect of increasing highway speed on fuel economy." February 8, 2013.

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