Study: EPA Understates Hybrid MPG By Up To 33 Percent

Hybrid vehicles may actually get much better fuel economy than their EPA-rated stickers say, according to a new study.

The analysis, conducted by Britt A. Holmén and Karen M. Sentoff with the University of Vermont, looked at the fuel consumption of a conventional Toyota Camry and compared it to a Camry Hybrid the same model year. But instead of using a controlled laboratory setting – as the U.S. Environmental Protection Agency does – the researchers tested the cars on a 32-mile course spanning city streets, an Interstate and rural roads.

Changing testing methods to real-life driving conditions increased fuel economy for the Camry Hybrid by as much as 33 percent, said Holmén and Sentoff.

“Our real-world … measurements suggest computed city cycle [conventional vehicle] fuel use would be nearly 2 times higher than for the [hybrid vehicle] and 1.3 times higher than the [hybrid vehicle] for highway driving,” the researchers said in their recently published paper. “These ratios exceed the factors that EPA fuel economy values would predict for these vehicle types.”

“Thus,” they added, “inclusion of real-world road grade and ambient conditions in our [vehicle specific power] and emissions measurements, compared to controlled laboratory tests, show fuel consumption benefits for the [hybrid vehicle] increased 18 percent and 33 percent (highway and city, respectively) compared to estimates based on EPA adjusted fuel economy “sticker” values.”


Comparing the fuel economy of a 2010 Toyota Camry Hybrid (left) and a 2010 Toyota Camry with a gasoline-only powertrain (right). Source:

The EPA-rating on the test car, a 2010 Camry Hybrid, is 33 mpg in the city and 34 mpg on the highway. Using the calculations from this study bumps the sticker-stated fuel economy up to about 44 city/40 highway. Such a significant gain in fuel savings would shorten length of time it takes for the hybrid powertrain to pay for itself, and could make hybrids a more attractive option for consumers.

According to the researchers, changing testing methods from a sterile laboratory setting to a course that emulates a variety of conditions found in everyday driving and adding additional hybrid models would yield more accurate fuel estimates.

“Prior studies are not well-suited to forecast the magnitude of current-technology [hybrid vehicles] on transportation energy use because the data were from laboratory studies of one or two early model [hybrid vehicles] (i.e., Toyota Prius, Honda Insight) compared to conventional vehicles of dissimilar make/model and vehicle size,” Holmén and Sentoff said.

“Our results with one vehicle pair demonstrate that similar studies can be used to develop robust models of all types of [hybrid] platforms under actual driving conditions and improve quantitative estimates of the future fleet contributions to the U.S. CO2 emissions inventory and petroleum consumption. Studies such as these are critical as [hybrid vehicles] and other electrified vehicles comprise a larger portion of the on-road fleet.”

SEE ALSO: Study Says Most Drivers Get Better Than EPA-Estimated MPG

As the duo mentioned, more research is necessary to see if these results are applicable to other hybrid vehicles. But with fuel savings potentially 33 percent higher than previously thought, it’s likely that others will step forward to further investigate the real-world fuel economies of electrified powertrains.

More information on the researcher’s testing methods and results can be read in their paper, “Hybrid-Electric Passenger Car Carbon Dioxide and Fuel Consumption Benefits Based on Real-World Driving.”


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