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Emission Facts: Calculating Emissions of Greenhouse Gases: Key Facts and Figures
EPA420-F-05-003 February 2005
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The U.S. Environmental Protection Agency (EPA) developed this series of four fact sheets to facilitate consistency of assumptions and practices in the calculation of emissions of greenhouse gases from transportation and mobile sources. They are intended as a reference for anyone estimating emissions benefits of mobile sources air pollution control programs.
- Average Fuel Economy
- Fuel Economy Estimates from MOBILE6
- Fuel Economy Estimates from FHWA
- Vehicle Miles Traveled Per Year
- Greenhouse Gas Emissions
- Global Warming Potentials
- Conversions
- Putting Transportation Greenhouse Gas Emissions Into Perspective
- More Information
Average Fuel Economy
EPA and the Federal Highway Administration (FHWA) use two different methodologies for calculating the average fuel economy of a passenger vehicle. Although MOBILE6 (EPA's computer model for estimating emissions for highway vehicles) estimates are more current, EPA uses the FHWA numbers in developing the greenhouse gas inventory because they are consistent with the methodology used to estimate carbon dioxide emissions.
Fuel Economy Estimates from MOBILE6
| (in miles per gallon [mpg]) | |
| Passenger car | 23.9 mpg |
| Light duty truck | 17.4 mpg |
| Passenger vehicle (cars and light trucks combined) | 20.3 mpg |
Source: MOBILE6 model run conducted in 2003, based on fuel economy test data from EPA’s annual Fuel Economy Trends Reports. Estimates are in-use fleet averages for 2003 vehicles and earlier. Estimates include all vehicles up to 25 years old. Note: These estimates do not include vehicles over 8500 pounds.
Fuel Economy Estimates from FHWA
| Passenger car | 22.1 mpg |
| Light duty truck | 17.6 mpg |
Source: FHWA "Highway Statistics 2001." 
Estimates are in-use fleet estimates obtained by dividing fleet total Vehicles Miles Traveled (VMT) by fuel sales in each category.
Vehicle Miles Traveled Per Year
| Typical passenger vehicle (cars & trucks combined) | 12,000 miles |
Source: Approximation from several sources. This estimate can be used for rough calculations. MOBILE6 can also provide annual mileage accumulation estimates for specific ages and classes of vehicles. VMT estimates can vary, and for purposes other than rough estimates, you should obtain estimates specific to your needs.
Greenhouse Gas Emissions
Passenger vehicle - 5.5 metric tons carbon dioxide (CO2) annually (= 1.5 metric tons carbon equivalent)
Source: Approximation for a typical passenger vehicle based on EPA calculation - see fact sheet EPA420-F-05-004 on greenhouse gas (GHG) emissions from a passenger vehicle. This value includes emissions of carbon dioxide, nitrous oxide, methane and hydrofluorocarbons. The estimate is of vehicle emissions only (i.e., it does not include lifecycle emissions from fuel processing or distribution). Note: This estimate does not include vehicles over 8500 pounds (lbs).
| CO2 emissions from a gallon of gasoline | 19.4 lbs |
| CO2 emissions from a gallon of diesel fuel | 22.2 lbs |
Source: Calculation based on 40 CFR 600.113 and Intergovernmental Panel on Climate Change (IPCC) methodology - see fact sheet EPA420-F-05-001.
Note: All estimates above are single point estimates, and have associated variation and uncertainty. In some cases it may be appropriate to use other values, or a range of values.
Global Warming Potentials |
| Carbon dioxide (CO2) | 1 |
| Methane (CH4) | 21 |
| Nitrous oxide (N2O) | 310 |
| Hydrofluorocarbon (HFC)-134a | 1,300 |
| (used in mobile source air conditioning) |
Source: IPCC Second Assessment Report (1996)
Conversions
1 metric ton of carbon equivalent = 3.667 metric tons CO2 eq.
1 metric ton of CO2 eq. = 0.2727 metric tons of carbon eq.
1 teragram = 1 million metric tons
1 kilogram = 2.205 pounds
1 metric ton = 1.102 tons
New Personal Vehicle Fuel Economy at 22-Year Low
(“Real World” fuel economy, 15% lower than CAFE value)
Putting Transportation Greenhouse Gas Emissions Into Perspective
2002 U.S. Greenhouse Gas Emissions by Sector
Source: Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 - 2002
2002 U.S. Transportation Sector by Category
Source: Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 -2002
Vehicle Miles Traveled Since 1970
(Trillions of Miles)
Source: FHWA Tracffic Volume Trends, December, 2002
For More Information
You can access documents on greenhouse gas emissions on the Office of Transportation and Air Quality web site at:
For additional information on calculating emissions of greenhouse gases, please contact Ed Coe at:
U. S. Environmental Protection Agency
Office of Transportation and Air Quality
1200 Pennsylvania Ave., NW (6406J)
Washington, DC 20460
202-343-9629
E-mail: Ed Coe at coe.edmund@epa.gov