This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Consumer tip-of-the-day: increasing efficiency of fuel economy on a miles-per-gallon scale is not linear, as more miles-per-gallon (mpg) are initially better for your wallet and the planet than you might expect, and eventually trail off with diminishing returns.
Last week, a friend pointed out a good blog post by Nicholas Chase and the Energy Information Administration (EIA), in which we glean several important points:
If you are considering the fuel economy of a vehicle you are purchasing, remember the non-linearity of the metric when comparing options, as you might be comparing apples to oranges. Whether or not mpg is a good metric in the first place, I’ll leave to others to discuss.
Moving from the current US fleet average of 25.5 mpg, as of June, to the mandated 54.5 mpg (equivalent to 163 grams/mile of CO2) by 2025 for light duty cars and trucks, is going to save a lot of energy. According to the EIA, the share of transportation energy use from light-duty vehicles is going to fall from 63% (2012) to 51% by 2040.
An implication of improving conventional vehicle fuel economy is that electric vehicles and other alternative fuel vehicles will face a harder time competing with conventional vehicles as they increase in efficiency. Of course, as I have pointed out before, zero-emission vehicles are a long-term ambition, and at some point we need to switch away from conventional vehicles, so this does not make the overall effort void, rather it highlights the importance of interim market share gains.
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Ultimately, this is all basic math, but as Nest seems to show, how you present information is often as important as what that information is in the first place. Another example is EPA’s on-going effort to convey how much you will save by buying a plug-in hybrid electric vehicle (PHEV). It’s quite an ambitious effort considering it is unclear how much you will drive in electric-versus-gasoline/diesel mode, but still: you have to start somewhere.
So next time you’re in the market for a new car, remember that the differences in fuel economy might be deceiving. For example, 22 mpg versus 20 mpg is not equal to a 10% increase in efficiency; in fact, you might be saving more than you think. Now multiply that out by the US light-duty vehicle fleet of 96.6 million, and you’ll see why initial fuel economy improvements are essential to reducing energy use in the US.
UPDATE: As suggested by reader Daniel Kolomeets-Darovsky, I've here included a fuel economy calculator which allows for quick-and-easy comparisons: http://www.fueleconomy.gov/feg/savemoney.shtml