Simanaitis Says

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THE FEDS have announced that Corporate Average Fuel Economy for cars and light trucks in Model Year 2025 will be 54.5 mpg. However, whenever politics meets technology, guess which wins? In particular, those looking forward to an average 2025 model achieving this kind of mpg are being misinformed.

This disinformation lurks in the difference between CAFE mpg values and the values in the EPA Fuel Economy Guide.

Assessment of fuel economy as well as emissions comes from operating the car through prescribed tests on a lab’s dynamometer. This is more accurate and reproducible than any road testing. Image from

They begin on a vehicle dynamometer (think a treadmill for cars), where the vehicle is operated through carefully orchestrated patterns of acceleration, cruising, braking and idling. The City and Highway tests are the two primary ones. Others have conditions of extreme temperatures or higher speed. Analyzing the exhaust gives a highly accurate fix on fuel consumed in each test.

Straightforward arithmetic comes up with a Combined value weighted 55 percent City/45 percent Highway. Over the years, EPA’s City and Highway values have undergone additional conditioning—fudging, if you like—all the better to reflect real world experience.

The EPA Fuel Economy Guide can be downloaded from

And, in fact, I generally find my actual driving—in essentially suburban enthusiast mode—yields 1-3 mpg better than a car’s EPA City number. I continue to believe that today’s EPA Fuel Economy Guide and a car’s Monroney label do an excellent job of communicating real world mpg.

However, the values used in CAFE calculations are the raw unconditioned data. It’s figured that EPA corrections bring these down by 20-25 percent.

The rest is arithmetic: A typical car averaging the 35.5 mpg of CAFE’s 2016 standard would deliver about 27.5 mpg in the real world.

And EPA has estimated that the 54.5 mpg embodied in 2025 CAFE would equate to a real fleet average of around 39 mpg. Part of this is attributed to CAFE giving mpg credits for things like advanced air conditioning and the like.

Hybrids are important in achieving 54.5 mpg, as are plug-ins, pure electrics, fuel cell cars and conventional ones featuring advanced technology.

A last comment: It isn’t that 55-mpg cars don’t exist: A Toyota Prius isn’t far from this today. And certainly advanced hybrids, pure electrics and fuel cell cars can achieve mpg-equivalent values well beyond this. Only the optimistic, however, see widespread adoption of these technologies between now and 2025. ds

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This entry was posted on August 30, 2012 by in Driving it Tomorrow and tagged , , , .
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