Saturday, January 31, 2009

A letter from Rep. James Sensenbrenner to EPA Aministrator Lisa Jackson

Representative James Sensenbrenner of Wisconsin has sent a letter to new EPA Administrator Lisa Jackson calling attention to the benefits of using gallons per mile as measure of fuel economy. Read the press release and letter here.

Rep. Sensenbrenner has also proposed support for hybrid trucks. Given the low MPG of trucks (delivery trucks, garbage trucks, etc.), we believe this makes a great deal of sense. GPM makes clear that even a modest MPG improvement on trucks will save tons of carbon over 10,000 miles of driving.

Quoting from the press release: "In reducing fuel consumption, our focus should start with the least efficient vehicles. Because trucks consume much greater quantities of fuel than cars, even seemingly modest efficiency gains result in substantial fuel savings," Sensenbrenner said. "Trucks consume 48 percent of our fuel and each individual truck consumes substantially more fuel than a passenger car. Trucks, not cars, are the low-hanging fruit, and trucks should be a primary focus of hybrid technology research."

The press release then describes the benefits of replacing conventional garbage trucks with hybrid garbage trucks. We think this is a compelling application of the GPM argument.

Coca Cola recently purchased 185 hybrid delivery trucks.

Friday, January 30, 2009

Cash for Clunkers 2

[Update June 20 2009

If you are considering a trade in,
please use the tools linked here to see the cash value of your gas savings. The gas savings can be more valuable than a Cash for Clunkers voucher.

The final bill is linked to this post. The details below refer to an older bill.]

Following up on this earlier post, I have tried to find out how much carbon dioxide is emitted in the process of manufacturing new cars. If this amount is substantial, it calls into question the GHG benefits of replacing inefficient cars with more efficient cars.

Honda reports that it emits less than a ton of carbon dioxide producing each vehicle. To put this number in perspective, a 20 MPG car will emit 50 tons of CO2 over 100,000 miles; a 30 MPG car will emit 33 tons of CO2. The ton of CO2 emitted when producing a new car is a trivial proportion of the CO2 emitted when driving.

Consistent with Honda's claim, this WRI report says that assembly accounts for 2% of total carbon emissions from cars.

The implication: The carbon emitted to produce a new car is not a compelling reason to oppose the Cash for Clunkers plan. Gas savings will make up for the manufacturing emissions in less than a year's worth of driving.

(May 7 Update: Bill Chameides, Dean of Duke's Nicholas School of the Environment, says that CO2 from manufacture is closer to 7 tons of CO2.)

See the blog archive on the right for newer posts on Cash for Clunkers.

Sunday, January 25, 2009

Cash for Clunkers is Being Weighed in Congress

[Update June 20 2009

If you are considering a trade in,
please use the tools linked here to see the cash value of your gas savings. The gas savings can be more valuable than a Cash for Clunkers voucher.

The final bill is linked to this post. The details below refer to an older bill.]

The Senate is now considering a Cash for Clunkers program, introduced by Dianne Feinstein, Susan Collins, and Charles Schumer. The bill has also been introduced in the House. The program works by subsidizing car owners who trade in a highly inefficient car for a car that is above average in efficiency.


Jason Bordoff of the Brookings Institution recently made the case for a Cash for Clunkers program in a Detroit Free Press Column and a Brookings Institution Paper, as did Dean Baker of CEPR at Truthout. Alan Blinder proposed a Cash for Clunkers program in July 2008 and reviews similar programs that have been implemented in several states.

GPM makes clear why this is a brilliant idea--the gas savings and CO2 reduction of removing a 14 MPG for a 25 MPG car is huge (3 tons of carbon dioxide over 10,000 miles). There is no possible improvement that can be made to a 33 MPG to reduce carbon emissions by that amount. And, of course, it is a way of stimulating car purchases during the current economic crisis.

25 MPG doesn't seem like much. But removing the 14 MPG cars is extremely valuable, and as important today as winning the X prize with a 100 MPG car tomorrow.....

The math:

14 MPG = 700 gallons per 10,000 miles
25 MPG = 400 gallons per 10,000 miles
33 MPG = 300 gallons per 10,000 miles

The 14 MPG to 25 MPG improvement eliminates 300 gallons per 10,000 miles, or 3 tons of carbon dioxide.

The net carbon impact of Cash for Clunkers must also take into account CO2 emissions from car production. Honda emits less than a ton of carbon dioxide to produce each vehicle. Based on Honda's numbers, replacing a 14 MPG car with a new 25 MPG car would be carbon neutral after 4,000 miles of driving, and would represent a net carbon reduction after that. (Update: More on the carbon consequences of new cars at this later post.)

Eric De Place at Sightline Daily endorses the idea.

There are a few moral hazard issues with this proposal that I'll let the economists sort out (i.e., junkers sitting in a yard are fixed up to make a couple of thousand dollars, but the car is worth less than the bounty, and removing it yields no carbon reduction). The proposal addresses this issue by requiring that the car be registered in the previous 120 days.

Sunday, January 11, 2009

GPM Calculator - With 2009 Car Information

MPG can be a misleading measure of fuel economy when comparing two cars. For a full explanation of why it is misleading, read the posts here and here. Focusing on gas consumption, and not MPG, gives you an accurate sense of fuel economy and carbon dioxide emissions.

If you are interested in a Cash for Clunkers trade in, use the calculator below or these charts to see the gas and cost savings of a trade.

The following calculator helps you convert MPG to "gallons per mile" (GPM) so that you can see the gas consumption of different cars. You can select a distance, gas price, and MPG level of your choice. You can compare the GPM of all new 2009 vehicles. Click the image to access the calculator.

The first calculator allows you to convert a car's MPG to GPM for an MPG level and distance of your choice. You will also be asked to enter a gas price to see the cost of driving that car for your chosen distance.

The second and third calculators allow you to compare the GPM of new 2009 vehicles. You will also be asked to enter a gas price to see the cost of driving the cars you are comparing. The MPG figures come from the EPA website (which provides an option for comparing cars based on gallons per 100 miles).

If you are interested in downloading excel sheets and printable tables that convert MPG to GPM, go to the section on this webpage called Tools for calculating GPM from MPG.

Burning one gallon of gas releases about 20 pounds of carbon dioxide (another 20 percent is released in producing gasoline). Every 100 gallons saved reduces carbon dioxide emissions by 1 ton.


Chris Shea summarized the argument for "Gallons per Mile" in the 2008 New York Times Magazine "Year in Ideas" issue.

Edmunds describes the shortcomings of MPG and offers a GPM calculator that lets you compare two specific car models in terms of "gallons per 100 miles" at (Note: Gallons per 100 miles is summarized as TFC for "True Fuel Consumption".)

If you would like a calculator that converts different combinations of metric (kilometers per liter, litres per 100 km), imperial gallons (as used in Britain), and US measures (such as MPG and gallons per 100 miles), this calculator and this calculator covers it all.

Monday, January 5, 2009

Teaching Materials

[Update September 2009: There are great "GPM" materials available here.]

The MPG Illusion can be a useful topic to discuss in a range of high school and college classes. It may be useful for:
  • Showing the link between psychology and climate change in an intro psych class
  • Showing framing effects (and debiasing) in a judgment and decision making class
  • Discussing consumer decision making in a marketing or environmental economics class
  • Illustrating a basic math concept (inverse relationships) with a consequential consumer decision.
Start by looking at the MPG Illusion teaching materials gathered at the terrific Social Psychology Network site. (These materials received an honorable mention for Action Teaching.) The SPN site is full of teaching resources, articles, and links related to social psychology and psychology in general.

Here are a few additional materials that overlap in part with the materials gathered at SPN:

Teaching notes - These notes focus on how to use quizzes and other materials to teach about the MPG Illusion in psychology classes. The MPG Illusion may also be of interest in economics and math classes.

Slides - These powerpoint slides contain quizzes, graphs and tables, results from the Science studies, and slides that connect the MPG Illusion to other topics.

Additional topics - These notes describe ways to use the MPG Illusion to lead into more general questions about greenhouse gas (GHG) decisions and about "nudges."

The following links are shorter, more memorable urls for the quiz, video, and calculator:

Math teachers: The NSF has a special report on math education that includes the MPG Illusion.