Initial estimates set the cost of the program between $1 billion and $2 billion a year. Feinstein’s bill envisions the program lasting for four years and encouraging the retirement of up to 1 million vehicles a year, while ultimately saving between 40,000 and 80,000 barrels of motor fuel a day.

In the first year of such a proposed program, a person trading in a vehicle that is model year 2002 or later would be eligible to receive $4,500 for purchase of a new vehicle, $3,000 for purchase of a used vehicle, or $3,000 for transit fare credit. For model-year vehicles 1999 to 2001, drivers would get… [etc.]

!!!

This whole subject of fuels and efficiencies is complex enough without having the added confusion about the words we use, and is not about Dave’s usage in the article.

Let’s agree that mpg is not a measure of efficiency. First, an obvious example: I think we would all agree a 40,000 GVW semi getting 6 mpg is more efficient than a Prius getting 60 mpg. Second: Engines only know about BTUs, not volumes. An engine running on diesel fuel weighing 7 pounds per gallon vs an engine using gasoline at about 6 pounds per gallon or LPG at about 4.5 pounds per gallon cannot be compared on a mpg basis. (In these three examples the heating values of the fuels is fairly close on a weight basis, circa 20,000 BTUs per pound) so it’s easy to convert an equitable basis.

Third: It gets worse. Ethanol is both denser (more pounds per gallon) than petroleum fuels but has fewer BTUs by both weight and volume. (That oxygen atom in the ethanol molecule in a sense tells you it has already been partially oxidized.) Getting out the old sliderule I figure a car getting 30 mpg on gasoline would get 29.1 with 10% ethanol and 22.4 mpg on 85% ethanol.

Fourth: What if some miles are powered by an electric utility? In the US 85% of our energy and about 72% of our electricity comes from fossil fuels, with 50% from coal alone. Among other large users, China and Japan, it’s even worse. In many cases a plug-in electric car gets infinite mpg because it runs on coal. And it is getting worse. In 2009 and 2010 China will add at least 100 gigs of conventional coal generation.

To put this in perspective, the Chinese probably replace all of Denmark’s emissions reductions since 1995 each month, Dave Cohn 5/7/09
Fifth: Let’s also have some perspective on how we talk about fuel quantities. While ethanol and biodiesel are only produced to offset petroleum we measure them in gallons/ year. Of course these numbers sound large to the public when being boasted. Divide those numbers by 15,330 to get petroleum barrels per day.
Sixth: Let’s stop saying “gas” when we mean gasoline. We should not have to go through the process brief as it might be of determining which is meant. Sometimes it isn’t brief.
Seven: Let’s agree that efficiency is Output/Input in consistent units and expressed as a percentage.
Eight: Let’s agree to not call hydrogen and storage batteries sources of energy, but recognize they are analogous to tanks, a way or place to store energy.
Nine: Seems there is misunderstanding of “fleet average MPG” or what the article labels “Actual Fuel Economy Level.” Take two vehicles: One gets 10mpg, the other gets 100 mpg. We can make the assumption that both vehicles use the same gallons per year, OR that both vehicles travel the same number of miles per year. In the first case our average mpg is 55. (10+100)/2=55. Using the second assumption we get an average mpg of 18.89. (1/mpg1 + 1/mpg2 = 2/mpgav). Solve for mpgav=2/(0.1+0.01) or 18.89 If there were a third and fourth vehicle each getting 50 mpg then 1/mpg1+1/mpg2+2/mpg3=4/mpgav. mpga=4/(0.1+0.01+0.04)=26.67. I have deliberately chosen extreme mpg differences for demonstration.
The expression given in the article tells us the government uses the equal miles method. It’s better than the equal gallons method but still imperfect. If I have a 15 mpg pickup and a 35 mpg sedan I am almost certain to put more miles on the car.