1

Emission

Facts

Office of Transportation

and Air Quality

EPA420-F-05-003

February 2005

Calculating Emissions of

Greenhouse Gases:

Key Facts and Figures

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

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
2

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 and trucks combined) 12,000 miles

Source: Approximation from several sources. This estimate can be used

for rough calculations. MOBILE6 can also provide annual milage

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, methane, nitrous oxide, 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
3

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

CO2 1

CH4 21

N2

O 310

HFC-134a 1,300 (HFC-134a is 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

 metric ton = 1.102 tons

New Personal Vehicle Fuel Economy 

at 22-Year Low

(“Real World” fuel economy, 15% lower than CAFE value)

18

19

20

21

22

23

24

198019821984198619881990199219941996199820002002

2003 Trends Report data - combined cars and trucks

Model Year

mpg
4

Putting Transportation Greenhouse Gas Emissions

Into Perspective

Transportation

27%

Agriculture

8%

Commercial

18%

Industry

30%

Residential

17%

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

Source mmt CO2e

Other nonroad 100.2 

Rail 33.9 

Boats 52.9 

Aircraft 179.4 

Mobile HFCs 40.3

Lubricants 10.8 

Buses 8.5 

Heavy Trucks 296.7

Passenger Cars, 1153

Light Trucks and 

Motorcycles (62% of transp. GHGs)

mmt = million metric tons

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%
5

Vehicle Miles Traveled Since 1970

(Trillions of Miles)

Source: FHWA Traffic Volume Trends, December, 2002

0

0.5

1

1.5

2

2.5

3

197019741978198219861990199419982002

For More Information

You can access documents on greenhouse gas emissions on the Office

of Transportation and Air Quality Web site at:

www.epa.gov/otaq/greenhousegases.htm

For further 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: coe.edmund@epa.gov