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Why Your Car May Get Better Gas Mileage Than You Think

by Joseph Szczesny, The Detroit Bureau /  / Updated 

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Consumer advocates have complained for years that EPA fuel economy tests, which are performed in a lab-like setting rather than on public streets, don't reflect the real-world performance of vehicles. The EPA itself has cracked down on various automakers, including Kia and Hyundai, for submitting data that overstated their cars’ mileage performance.

But when engineers from the American Automobile Association analyzed gas mileage records submitted to the EPA by actual drivers, they found something surprising.

In the self-reported data, covering 37,000 mileage records and 8,400 different types of cars, AAA’s analysis showed that eight out of 10 drivers reported mileage that was higher than the official combined city and highway EPA mileage rating.

“The vast majority of drivers that submit their vehicle’s fuel economy to the EPA report mileage that beats the window sticker rating,” said John Nielsen, AAA’s managing director, Automotive Engineering and Repair. “Although self-reported data has limitations, it’s encouraging to see real-world fuel economy that more closely aligns with, or even exceeds, automaker promises.”

Owners of certain categories of engines, such as powertrains with manual transmissions, diesel and big V8 engines found in trucks, all self-reported better fuel-economy numbers that those automakers reported to the EPA.

For example, owners of vehicles equipped with manual transmissions reported 17 percent higher fuel economy than EPA ratings. The owners of diesel-fuel vehicles, including light trucks, reported 20 percent higher fuel economy.

Meanwhile, truck owners with gasoline-fuel V-8 engines reported fuel economy 5 percent higher than EPA ratings, while owners of turbocharged V-6 engines reported fuel economy that was 9 percent lower.

AAA engineers, who were conducting the analysis as part of the organization’s annual mileage survey, identified a list of vehicles that were frequently reported as failing to achieve the EPA’s mileage rating. The majority of these vehicles, including the scrutinized Hyundai and Kia models, have since been retested and, in some cases, mileage ratings were revised. AAA selected three additional vehicles – a 2014 full-size pickup truck, a 2014 large sedan and a 2012 medium sedan –- for further testing.

The AAA analysis of data collected on the EPA’s FuelEconomy.gov website, along with laboratory and real-world vehicle testing, found that driver behaviors and environmental conditions, rather than vehicle shortcomings, are likely responsible for most fuel economy variances.

In partnership with the Automobile Club of Southern California’s Automotive Research Center, AAA tested the vehicles independently to verify the fuel economy. Over the course of several weeks, testing was conducted using a certified dynamometer and on the streets of Southern California. Test results from of all three vehicles confirmed the EPA mileage rating was accurate, leaving AAA to conclude that driving behaviors, vehicle condition, driving environment and terrain are likely responsible for most deviations from EPA ratings that consumers experience.

“In addition to logging hundreds of miles in various driving environments, the research team put the vehicles through EPA-specified testing designed to mimic the real-world conditions, including city, highway and aggressive driving,” said Megan McKernan, manager of the Automobile Club of Southern California’s Automotive Research Center. “The findings indicate that while vehicles tested are capable of achieving the EPA rating, a driver’s real-world mileage will vary based on driving style.”

Every year, as part of its annual fuel economy testing series, AAA tests 10 to 15 percent of commercially available vehicle models. In the next phase of this year’s testing, to be released in late 2015, researchers will measure the impact that specific driving behaviors, such as acceleration rates and idle time, have on an individual driver’s fuel economy. In the meantime, AAA recommends that drivers take a closer look at their driving habits to understand the role they play in the fuel efficiency of their vehicle.

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