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What Will the New Standards Actually Mean for the Fuel Economy of New Car Models in the Real World

Ask a Scientist - January 2012

B. Von Holle from Oviedo, FL, asks “When I read about the government’s stricter fuel efficiency and global warming pollution standards for new cars, the numbers in the press accounts sounded too good to be true. The skeptic in me wondered: are they artificially inflated somehow? What will the new standards actually mean for the fuel economy of new car models in the real world?” and is answered by Clean Vehicles Senior Engineer Jim Kliesch.

On the one hand, you are right to be skeptical. The numbers used in the government standards, and often echoed without explanation in the press, do differ substantially from the miles per gallon new car models will actually achieve on the road, for reasons I will try to explain. That being said, however, don’t let your skepticism obscure the fact that these new standards are very good news for the planet. Once fully implemented, the new standards will require automakers to produce vehicles that emit roughly half the global warming emissions produced by today’s new automobiles. In 2030 alone, that will keep 290 million metric tons of carbon dioxide from being released into our atmosphere annually—equivalent to taking more than 40 million of today's cars and trucks off the road for an entire year. In terms of fuel economy, the standards will cut U.S. oil consumption in 2030 by 1.5 million barrels of oil per day. That’s more than we currently import from Saudi Arabia and Iraq combined.

So, we at the Union of Concerned Scientists count the new standards as a major victory in the fight against global warming and U.S. oil dependence.

Now, though, let me try to explain the discrepancy that you are right to point out between the numbers used in the standards and the fuel economy numbers you’ll see on the window stickers of new cars in the showroom in the years to come.

The tests used to determine compliance with the national global warming and fuel economy standards were developed about 40 years ago. Since then, however, much has changed. Today’s driving styles include faster acceleration and higher driving speeds than four decades ago, neither of which is captured on the tests. The same is true for some gas-consuming features that were rare then but have since become commonplace, such as air conditioning. So, even though the outdated tests are required by the law on the books, they produce miles-per-gallon (mpg) figures that run, on average, about 28 percent higher than the actual rates you would receive driving today’s cars on the road. This means, for instance, that a vehicle that earned 54.5 mpg on the tests used for compliance with the new standards would actually achieve 36-39 mpg on the road, depending on how the automaker decides to meet the standard.

To make matters even more complicated, the 54.5 mpg estimate is a predicted average of the entire industry’s fleet of cars and trucks. The requirements for individual vehicles will vary greatly, depending on how large the vehicles are, and whether they are classified as cars or trucks. Finally, in order to encourage automakers to improve their fleets’ efficiency, the standards are written to incentivize certain behaviors. For instance, automakers producing electric vehicles can lower their averages because these electric vehicles will be counted by the government as producing zero emissions. The global warming standards allow automakers to get extra credit toward compliance in other ways too, such as by making low-leakage air conditioning systems.

So, those kinds of realities account for much of the discrepancy you noted. The table below shows how the government’s so-called CAFE (Corporate Average Fuel Economy) mpg numbers stack up against the considerably more accurate mpg numbers the Environmental Protection Agency (EPA) requires automakers to display on new car windows. The numbers show that, while it will be almost 15 years before the new global warming pollutions standards are fully phased in, automakers are already offering models that exceed the 2025 levels. Moreover, some 39 models in showrooms now are available in a version that meets its 2017 fuel economy target. In other words, we already have the technology we need to make vehicles that are cleaner and more fuel efficient. We just need to use it more widely.

CAFE and Window Label MPGs for Select Vehicles

 Model Year 2011 Vehicles   

 CAFE Test (mpg)  Window Label (mpg)
 Toyota Prius    71  50
 Honda Civic Hybrid  59  41
 Ford Fusion Hybrid  54  39
 2025 Standard (1)  47  35
 Hyundai Elantra  44  33
 Chevy Cruze Eco (manual)  44  33
 Ford Escape Hybrid 4wd  44  32
 Honda Civic  40  29
 2016 Standard (2)  35  26

Source: 2011 Fuel Economy Guide data file available at http://www.fueleconomy.gov/feg/download.shtml.
Notes: (1) 163 g/mi CO2-e standard proposed for 2025. Translation to mpg assumes use of A/C credits and 5 percent electric vehicle sales. (2) Existing 250 g/mi CO2-e standard.

Jim Kliesch is an engineer with expertise in clean and efficient vehicle technologies. He holds a bachelor's degree in electrical engineering from Ohio University, and a master's degree in environmental and energy policy from the University of Delaware.

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