Now that the federal government has at last firmed up the fleet average fuel economy and CO2 standards for the next five years, you might wonder how much vehicle models will have to improve to meet those mandates. In a surprising number of cases, it might not be as much as you think.

Why? There is a dirty little secret that no one actually likes to talk about considering fuel economy regulations. You might have noticed in 2008 that the mileage estimates that appear on new car window stickers dropped significantly. That's because the EPA has included a number of adjustment factors and new test cycles designed to provide a more accurate real world mileage estimate. However in order to provide a means to measure improvement over time, NHTSA continues to use the old two-cycle (city and highway) test results without adjustment for the purpose of determining the fleet average for every automaker. The 34.1 mile per gallon figure for CAFE is roughly equivalent to a current EPA combined sticker value of 26-27 mpg. More precisely, cars will have to hit 37.8 mpg and truck 28.8 mpg (again, unadjusted). Those correspond to approximately 30-31 and 21-22 mpg, respectively, on the old system. A NHTSA official told us on background:
There is not a direct way to estimate label fuel economy based on CAFE fuel economy. Fuel economy levels used for CAFE are based on combined "unadjusted" EPA city cycle laboratory test use of adjustment factors and is displayed on the label as individual city and highway fuel economy numbers, but is not as combined fuel economy data and "unadjusted" EPA highway cycle laboratory test data. EPA label fuel economy is based on 5 cycle testing.
That means that mid-size cars like the Toyota Camry hybrid, Ford Fusion hybrid and smaller cars like the Mini, Toyota Yaris and Honda Fit all easily top the standard. Of course, the companies also have to factor in larger cars like Ford Taurus and Toyota Avalon to meet the fleet average, which means that many cars will still have to improve in efficiency, just not as much as you might think.

Similarly, trucks like the Ford Escape hybrid, Toyota Highlander hybrid and Lexus RX450h all hit the threshold and even the GM two-mode hybrids are on the cusp. That still leaves the high volume non-hybrid trucks and SUVS below the limit, so they will have to come up to make the average.

[Source: NHTSA | Image: richardmasoner - C.C. License 2.0]

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