Is A 5% Annual Improvement in MPG Possible?

March 21st, 2012 | 2 Comments »

Optimism rules when it comes to future automobile fuel economy. Consider President Obama’s 2008 campaign pledge to provide one million 150 MPG plug in hybrid cars by 2015. After spending about $4 billion we don’t have a single 150 mpg car running today nor are there any announced. There are claims of 100 MPGe (where the small e stands for “equivalent”) cars. But the small e subscript next to MPG represents an EPA accounting method which ignores the energy used to generate electricity as well as the CO2 emitted during the electricity generation process. As of early 2012, there have been about 20,000 plug-ins shipped which average around 40 MPG when upstream energy consumption is included.

President Obama and Vice President Biden have long been concerned about energy. Early in 2007, Biden, with Barack Obama (D-IL) and several other senators introduced the Fuel Economy Reform Act with the goal of increasing fuel economy standards by 4.0% annually for cars built between 2009 and 2011.[1] In July 2011, President Obama announced a deal with the automobile companies calling for a 5.0% average annual increase in fuel economy for cars and a 3.5% annual increase for light trucks through 2021.[2] After 2021, both cars and trucks would have to provide a 5.0% annual increase.

Our politicians may call for major yearly fuel economy increases but getting it done is not so easy. One cannot simply legislate a price/performance goal for a car or an airplane. Technology has its own rate of change relative to efficiency. And it requires a long testing process in the marketplace. The government tried before to set performance measures with its Program for A New Generation of Vehicles under the Clinton administration.[3] The result was an 80 MPG diesel hybrid car which was unaffordable because it cost so much to make. In the same time period, Toyota and Honda developed 42 MPG gasoline hybrid vehicles which have been very successful. The government has had lots of experience at developing high performance military systems where price is not a consideration. That’s OK for a limited number of products in relatively small numbers. The same philosophy cannot be applied to consumer items such as cars where price is important.

It is worthwhile to consider the historical efficiency improvement trends for different technologies to estimate what is possible. The following six figures were taken from an energy study on trends in Organization for Economic Co-operation and Development (OECD) countries (Australia, Austria, Belgium, Canada, Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Japan, Republic of Korea, Luxembourg, Netherlands, New Zealand, Norway, Portugal, Spain, Sweden, Switzerland, Turkey, United Kingdom and United States. [4]  The measure is in Exajoules. The results are roughly the same as U.S. trends. Figures 1 through 6 show different energy applications with a graph on the left showing the improvement in energy efficiency from 1973 to 1990. A bar chart on the right shows the average annual percent efficiency improvement for two different periods, the first period being from 1973-1990 and the second period from 1990 – 2004. For all sectors (Figure 1) the average in the second period was about 1.0% per year. For automobiles (Figure 6) the average for the second period was 0.5%.



Figure 1: Long-term Energy Savings from Improvements in Energy Efficiency
All Sectors




 Figure 2: Long-term Energy Savings from Improvements in Energy Efficiency Manufacturing Sector




Figure 3: Long-term Energy Savings from Improvements in Energy Efficiency
Household Sector





 Figure 4: Long-term Energy Savings from Improvements in Energy Efficiency
Services Sector





Figure 5: Long-term Energy Savings from Improvements in Energy Efficiency
Freight Efficiency Sector





Figure 6: Long-term Energy Savings from Improvements in Energy Efficiency
Passenger Transport (Automobiles) Sector



The figures shown are for the OECD nations which include the U.S. However, it is important to understand efficiency improvements for the U.S. alone. From 1970 to 2009, a forty year period, the energy used per vehicle mile for American vehicles decreased at an annual rate of 1.3% for Automobiles and 1.5% for Light Trucks.[5] This is similar to the first period shown in Figure 6. But in the eleven year period from 1999-2009, the energy used per vehicle mile for American vehicles decreased at an annual rate of 0.6% for automobiles and 0.4% for light trucks. This is roughly the same rate of energy efficiency improvement as that obtained in OECD nations in the most recent period. Note that for both the OECD and the U.S., the energy efficiency improvements have declined over time, an example of the “law of diminishing returns”.

Fuel economy improvements are also reported annually by the EPA. Figure 7 is a summary of a table in the EPA’s March 2012 report “Light-Duty Automotive Technology, Carbon Dioxide Emissions, and Fuel Economy Trends: 1975 Through 2011”. Between 1975 and 1987 there was a large increase in fuel economy from 13.2 MPG to 22 MPG, representing about a 4.0% annual improvement. In the 24 year period after that, from 1987 to 2011, fuel economy hardly improved at all.

 Figure 7: EPA March 2012 Report



Certainly some kind of crash effort might be able to improve this. But it also might only be marginal. Consider the huge investment in the current Chevrolet Volt and its very limited market acceptance.

A 5.0% per year improvement is highly unlikely based simply on energy efficiency technology. One needs the market experience of a million cars being driven for several years to determine feasible fuel economy improvements. Market experience might suggest a 1-2% annual improvement if everything went perfectly. President Obama’s 5.0% improvement number goes along with his 150 MPG plugin hybrid vision – way too optimistic.


[1] H.R. 1506: Fuel Economy Reform Act
Sizing Up Obama’s Fuel Economy Standards by Amy Harder, August 1, 2011
Running on Fumes by Elizabeth Kolbert, The New Yorker, November 5, 2007,
Energy Use in the New Millennium – Trends in IEA Countries, International Energy Agency, © OECD/IEA, 2007, Pages 152-154 9 rue de la Fédération, 75739 Paris Cedex 15, France.
Transportation Energy Data Book 30th Edition by Stacy Davis, Susan Diegel, Robert Boundy, Oak Ridge National Laboratory and Roltek, Inc. Table 2.13

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