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Americans are buying more efficient cars – in one graph

The views expressed are those of the author and are not necessarily those of Scientific American.


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CAFE standards are working, at least according to a research note from the University of Michigan. The graph below shows the average sales-weighted MPGs by month and model year. That is, the graph shows average MPGs from window stickers (between city and highway) weighted by vehicle sales. The average MPG of all cars sold has increased with every model year and is up nearly 5 MPG since 2007.

CAFE, which stands for Corporate Average Fuel Economy, is federal regulation that requires automakers to increase the fuel economy of their fleet, meaning an auto maker can have cars (and trucks, which have separate standards) that are both really efficient and not so efficient. But as long as they sell enough of the more efficient cars, their fleetwide average will be high enough. The formula for setting MPG targets for different sized cars has gotten more robust in recent years and now depends on the vehicles footprint.

The standard dates back to 1975 when the United States government intended to raise MPGs after the Arab Oil Embargo. The rule has been updated since then, most recently in 2009 and 2012 by President Obama. The target for 2011-2016 model years plateaus at 35.5 MPG while the standard increases to 54.5 MPG by 2025.

David Wogan About the Author: An engineer and policy researcher who writes about energy, technology, and policy - and everything in between. Based in Austin, Texas. Comments? david.m.wogan@gmail.com Follow on Twitter @davidwogan.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. jtdwyer 3:11 pm 03/4/2014

    The chart illustrates only the est. mileage for new cars sold. That’s meaningful only to the extent that new cars sold contribute to the total gallons consumed for all miles driven.
    According to the US Bureau of Transit Statistics for 2006, there were at that time 250,844,644 registered passenger vehicles in the US. The average age of registered passenger cars is increasing.
    In the U.S., 2013 new auto sales climbed 7.6% to 15.6 million. That’s a small percentage of annual global new auto sales:
    2013: 82.8 million
    2012: 79.5 million
    2011: 76.7 million
    2010: 73.2 million
    Source: IHS Automotive

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  2. 2. davidwogan 3:21 pm 03/4/2014

    Right. It’s not the actual reported MPG from purchased cars, but an average of the window sticker for all cars sold. Still, the main takeaway holds.

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  3. 3. jtdwyer 7:32 pm 03/4/2014

    davidwogan,
    I think the main point should be, how are new cars’ fuel economy improvements affecting the total miles per gallons consumed by all cars being driven.
    For example, according to http://www.fhwa.dot.gov/policyinformation/travel_monitoring/tvt.cfm there were 2,938.5 billion vehicle miles of travel in 2012, compared to 3,003.2 billion miles traveled in 2007.
    According to http://www.eia.gov/tools/faqs/faq.cfm?id=23&t=10 there were an estimated 133 billion gallons of gasoline sold to consumers in U.S. in 2012, compared to 142.35 billion gallons consumed in the peak year, 2007.
    The total MPG of gasoline for all miles traveled in 2012 is 22.1 compared to 21.1 in 2007 (not considering diesel or electric vehicles). While the fuel efficiency of new cars is improving significantly, its effect on total fuel efficiency is not yet as significant. It’s expected to continue to improve as less fuel efficient cars are ‘retired’.

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  4. 4. davidwogan 12:06 am 03/5/2014

    I don’t disagree with you. And just to be clear, the graph above is not for all cars on the road in a given month, but just those sold. So the actual MPG will be lower for the reason you point out (among many other reasons!): there are older, less efficient cars on the road. This is also the idea behind programs like Cash-for-Clunkers: cars have useful lives of 7-10 years.

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  5. 5. jtdwyer 3:56 am 03/5/2014

    Just pointing out that the good news – that Americans are buying more efficient cars – is not quite as good as it might seem at face value. BTW, the average age of cars on the road is more than 11 years…
    Thanks

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  6. 6. davidwogan 10:33 am 03/5/2014

    I believe that. I drive a 2001…

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  7. 7. Shamburg 11:34 am 03/5/2014

    With the computerization of cars, it’s surprising that the economy isn’t higher. With mechanical engines (pre-late-80s), timing, (when the sparkplug fires before TDC – top dead center) was only accurate at one speed. With the ability to monitor speed (RPM) and adjust the time of firing, efficiency (completeness of combustion) improves. Add fuel injection (as opposed to a piston sucking fuel/air into the cylinder) and the other computer controlled functions on a modern engine, is improved. Add the other improvements (e.g. carburetor mixing fuel and air) and I would expect greater improvements in efficiency.

    We used to love the sound of the dragsters lopping and barely staying running on the start-line, waiting for the green light of on the Christmas tree. With modern computerized engines, we should never hear that again (I must say, I’m sorry for that).

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