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Each vehicle reaches an optimal fuel economy at a different speed or range of speeds. A recent study by Oak Ridge National Laboratory illustrates that point with a wide range of data collected on 74 light vehicles. The figure below shows that from 50 to 60 miles per hour (mph) 26 of the vehicles experienced an 11-13% decrease in fuel economy, but one vehicle only experienced a 5-7% decrease, and two experienced a 17 to 19% decrease. From 60 to 70 mph, a fuel economy decrease of 13-15% was most common, and from 70 to 80 mph, a fuel economy decrease of 15-17% was most common.

Fuel Economy Penalty in Ten-Mile-Per-Hour Increments Notes:
Three graphs showing the fuel economy penalty in ten-mile-per-hour increments (50-60 mph, 60-70 mph, and 70-80 mph). See table below for more detailed information.
  • There were only 68 vehicles used for the 70 to 80 mph analysis; six vehicles were tested only to 70 mph.
  • The study included two-seaters, sedans, station wagons, sport utility vehicles, pickup trucks, and minivans of model years (MY) 2003 to 2012 with a wide variety of powertrains.
  • Dynamometers were used simulating highway cruising speeds on flat roads with moderate temperatures.
  • From 70 to 80 mph, there are several vehicles that show more than a 21% decrease in fuel economy; these values mainly come from vehicles with cylinder deactivation. Cylinder deactivation is a fuel saving technology that allows engines to deactivate cylinders under normal cruising conditions. The switch from using 4 cylinders at cruising speed to 8 cylinders at cruising speed causes a large change in fuel economy.

Supporting Information

Fuel Economy Penalty in Ten-Mile-Per-Hour Increments
Percent Decrease Speed Increments
50 to 60 mph 60 to 70 mph 70 to 80 mph
Number of Vehicles
5-7% 1 0 0
7-9% 2 1 0
9-11% 17 10 1
11-13% 26 15 14
13-15% 17 22 18
15-17% 9 16 19
17-19% 2 8 10
19-21% 0 2 1
21-23% 0 0 2
23-25% 0 0 2
25-27% 0 0 1
Total 74 74 68
Source: Green Car Congress, "ORNL researchers quantify the effect of increasing highway speed on fuel economy," February 8, 2013.

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