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I was wondering about the effectiveness of programs such as the one described at




wherein "Customers can turn a $500 trade-in car into a $4,500 trade-in by getting up to $4500 from the governments automotive stimulus program the public has called "Cash for Clunkers" - a program that allows consumers with older, less fuel efficient vehicles to trade in their "clunker" for a voucher worth up to $4,500 toward the purchase or lease of a new car with improved gas mileage of between 1 and 10 miles per gallon, depending on the vehicle purchased.  The official name is the Car Allowance Rebate System (CARS)."


For example, suppose I am in a position to consider the purchase of a more fuel efficient vehicle. Using a simplified, macroeconomic approach, I could ask the following questions:


How much energy does it take to deliver the item to market?


Energy Information Administration, Changes in Energy Intensity in the Manufacturing Sector 1985 - 1994 - In 1985, manufactures consumed, on average, 5.34 thousand British thermal units (Btu) for every dollar of products shipped (1992 constant dollars). This ratio inched to 5.44 in 1988, 5.51 in 1991 and settled at 5.49 in 1994.


I might even ask, "How much oil is consumed for purposes other than energy production?" for example, as raw material for the production of plastics.


Energy Information Administration, Annual Energy Review 2008 - Figure 1.15 Fossil Fuel Consumption for Nonfuel Use As Share of Total Energy Consumption, 2008: 5.4%


However, I also want to consider one more thing, "How am I going to earn the money to pay for this car?"


Wikipedia, Energy Intensity - U.S. energy consumption in 2004 was estimated at 99.74 quadrillion Btus (1.05 × 1011 GJ) (referred to as 'quads') from all sources (US DoE). Total GDP was estimated at $11.75 trillion in 2004 and US GDP per capita was estimated at roughly $40,100 in 2004 (CIA Factbook). Using a population of 290,809,777 (as per US Census Bureau). This would produce an Energy Intensity of 8,553 Btus (9 MJ)consumed to produce a single dollar of GDP.


Typically, I will be working to produce other goods or services in exchange, at an energy expenditure of 8553 Btu per dollar earned. Therefore, the total amount of energy expended in the purchase of a manufactured good in the U.S. might be approximately 8500 + 5500 = 14000 Btu per dollar.  If the new car will cost 20000 $, and it takes 14000 Btu to complete the transaction, then purchase of the automobile will likely result in the consumption of 280000000 Btu of energy. Since I am concerned with saving gasoline, and to help put things in perspective, this would be equivalent to roughly 2435 gallons of gasoline.


Where does this energy come from?


Wikipedia, Energy in the United States - The majority of this energy is derived from fossil fuels: in 2005, it was estimated that 40% of the nation's energy came from petroleum, 23% from coal, and 23% from natural gas. Nuclear power supplied 8.4% and renewable energy supplied 7.3%, which was mainly from hydroelectric dams although other renewables are included such as wind power, geothermal and solar energy.


As a worst case scenario, let us assume that I am only concerned with saving petroleum, and am quite content to continue using coal and natural gas, nuclear, etc. The petroleum share of energy consumed in the manufacture of a 20000 $ car would be 40% of 280000000 Btu, or 974 gallons of gasoline.


In effect, if I plan to drive the new car 100000 miles before the end of its life, and I have assumed a 974 gallon petroleum debt through the purchase of it, I must save about one gallon every 103 miles. If the new car gets 50 miles per gallon, it would take about 2 gallons to make this 103 mile trip. In order for me to have saved the gallon, the old car would have had to use 3 gallons to complete the same 103 mile trip, and would therefore be getting 34 miles per gallon instead. In other words, if the old car is getting less than 34 miles per gallon, the purchase of the new 50 mile per gallon car makes sense.


What if, in the interest of reducing carbon emissions, the goal is to save all fossil fuel, not just petroleum? Then I must try to save 85% of 280000000 Btu, or 2070 gallons of gasoline.


100000 miles per 2070 gallons = 48 miles per gallon saved

48 miles at 50 miles per gallon = 1 gallon consumed

48 miles per 2 gallons consumed instead = 24 miles per gallon threshold for a net energy savings


Although the numbers used in this example may be nebulous at best, (I will likely continue to use energy even though I am unemployed) there is an important underlying consideration that may be worth noting. It seems counterintuitive, but the more I desire to save energy, the less likely it is to make sense for me to purchase a more energy efficient new car.


Can anyone help me see it differently?

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Replies to This Discussion

Very good Ehben, thank you for posting this.

Tangent: Reminds me of Ivan Illich, who said the average American travels at the speed of 5 mph when calculating all the time and energy that goes into attention to our cars. He didn't share his math, however, as you have done here. Very interesting essay, though and worth reading in its entirety.

"The model American male devotes more than 1600 hours a year to his car. He sits in it while it goes and while it stands idling. He parks it and searches for it. He earns the money to put down on it and to meet the monthly installments. He works to pay for gasoline, tolls, insurance, taxes, and tickets. He spends four of his sixteen waking hours on the road or gathering his resources for it. And this figure does not take into account the time consumed by other activities dictated by transport: time spent in hospitals, traffic courts, and garages; time spent watching automobile commercials or attending consumer education meetings to improve the quality of the next buy. The model American puts in 1600 hours to get 7500 miles: less than five miles per hour. In countries deprived of a transportation industry, people manage to do the same, walking wherever they want to go, and they allocate only 3 to 8 percent of their society's time budget to traffic instead of 28 percent. What distinguishes the traffic in rich countries from the traffic in poor countries is not more mileage per hour of lifetime for the majority, but more hours of compulsory consumption of high doses of energy, packaged and unequally distributed by the transportation industry."
I also am not convinced that purchasing new ''gas saving" vehicles actually reduces the useage of fossil fuels consumed during both its production & useage. And the cultural and environmental effects of mining for the new materials is also not calculated into the formulas.

My intuition and values led me to purchase a used 8 yr old 1977 toyota corona wagon back in 85 and I kept it running for over 25 yrs of its life and over 200 K miles. I must have developed this habit of caring for mechanical items early in my twenties as I stll have my 1979 bicycle that continues to roll as long as I keep a few parts replaced, and riding downhill I go faster than 5 mpg.

I would rather see my tax money go towards helping to make repairs on vehicles.


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