„Fast
racts
U.S.Transportation Sector
Greenhouse Gas Emissions
1990-2021
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Office of Transportation and Air Quaiity
EPA-420-F-23-016
June 2023
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Mobile Sources
Transportation
Non-Transportation Mobile
Highway Vehicles
Agricultural Equipment
Aircraft
Construction & Mining Equipment
Ships & Boats
Lawn & Garden Equipment
Rail
Logging Equipment
Lubricants
Recreational Equipment
Pipelines1
Transportation Emissions of the United States
The transportation sector is one of the largest contributors to anthropogenic greenhouse gas
(GHG) emissions in the United States. According to the Inventory of US. Greenhouse Gels Emis-
sions and Sinks 1990-2021 (the Inventory), the national inventory that the U.S. prepares annually
under the United Nations Framework Convention on Climate Change (UNFCCC), the transpor-
tation sector accounted for the largest portion (29%) of total U.S. GHG emissions in 2021. Cars,
trucks, commercial aircraft, and railroads, among other sources, all contribute to transportation
end-use sector emissions. Within the sector, light-duty vehicles (including passenger cars and light'
duty trucks) were by far the largest category, with 58% of GHG emissions, while
medium- and heavy-duty trucks made up the second largest category, with 23% of emissions.
Between 1990 and 2021, GHG emissions in the transportation sector increased more in absolute
terms than any other sector (i.e., electricity generation, industry, agriculture, residential, commer-
cial), due in large part to increased demand for travel.
Greenhouse gas emissions from transportation sources include carbon dioxide (C02), methane
(CH4), nitrous oxide (N20), and various hydrofluorocarbons (HFCs). C02, CH4, and N20 are all
emitted via the combustion of fuels, while HFC emissions are the result of leaks and endoflife
disposal from air conditioners used to cool people and/or freight.2
When including emissions from non-transportation mobile sources such as agricultural, lawn
and garden, and construction equipment, mobile sources constituted 32% of total U.S. GHG
emissions in 2021.
Share of U.S. GHG Emissions
by Economic Sector, 20213'4
Note: Totals may not add to 100% due to rounding.
Share of U.S. Transportation Sector
GHG Emissions by Gas, 2C214
Note: Totals may not add to 100% due to rounding.
Share of U.S. Transportation Sector
GHG Emissions by Source, 2C214'5
Note: Totals may not add to 100% due to rounding.
Light-Duty
Vehicles
All Other
Transportation
Sources
6%
Ships & Boats
3% v
Aircraft
8%
1 Pipeline emissions in the transportation sector include only C02 from the combustion of natural gas at compressor stations that power
natural gas pipelines, not emissions from electricity use, non-C02 gases, or other types of pipeline equipment. Not that natural gas pipeline
compressor stations are stationary equipment that are included in the transportation sector, but are not considered mobile sources.
2 C02 emissions from the combustion of biofuels are not directly included in the energy sector contribution (which includes the contribution
of transportation and non-transportation mobile sources) to U.S. totals in the Inventory; instead, net carbon fluxes from changes in biogenic
carbon reservoirs are accounted in the estimates for Land Use, Land-Use Change, and Forestry in the Inventory. See Page 4 for more
information on the Inventory.
3 For presentation purposes, emissions from territories which constitute less than 1% of the total U.S. GHG emissions, are not shown in
this chart, although they are included in the total emissions used to calculate the percentage share of emissions from each sector.
See Table ES-5 in the Executive Summary of the Inventory for official data. See page 4 for more information on the Inventory.
4 "Transportation" emissions in these pie charts include C02, N20, CH4, and HFCs from domestic transportation sources like highway
vehicles, aircraft, ships and boats, rail, pipelines and lubricants. They do not include emissions from international bunker fuel use by
aircraft and ships or from non-transportation mobile sources such as agriculture and construction equipment.
5 "Other" sources include buses, motorcycles, pipelines, and lubricants.
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U.S.Transportation GHG Emissions
(Tg C02 Equivalent)
Change from
1990 to 2021
U.S.Transportation GHG Emissions by Gas, 2021
(Tg C02 Equivalent)
Absolute Percent
On-Road Vehicles
1,202.0
1,637.9
1,535.1
1,557.9
1,549.1
1,374.1
1,496.4
294.4
24.5
Passenger Cars
648.4
564.4
392.7
398.7
395.5
341.7
374.2
-274.2
-42.3
Light-Duty Trucks
302.5
659.5
716.2
720.6
711.8
615.4
671.8
369.4
122.1
Motorcycles
3.4
5.0
7.2
7.4
7.5
6.7
7.5
4.1
120.9
Buses
13.4
17.7
23.4
24.4
24.8
23.6
25.7
12.3
91.5
Medium- and Heavy-
Duty Trucks
234.3
391.3
395.6
406.7
409.5
386.7
417.1
182.9
78.0
Aircraft
188.8
193.3
174.6
175.3
183.4
123.0
155.4
-33.4
-17.7
Commercial Aviation
110.8
133.8
129.0
130.7
137.8
92.0
120.0
9.2
8.3
Military Aircraft
36.0
19.9
12.6
12.2
12.3
11.8
12.6
-23.4
-65.0
General Aviation
42.0
39.6
32.9
32.4
33.3
19.2
22.8
-19.1
-45.6
Ships and Boats
47.0
45.5
43.8
41.1
40.0
32.4
50.2
3.3
6.9
Rail
39.0
51.4
41.3
42.5
39.7
34.0
35.2
-3.7
-9.6
Pipelines6
36.0
32.6
41.6
50.2
58.2
57.9
64.2
28.2
78.4
Lubricants
11.8
10.2
9.6
9.2
8.8
7.8
8.0
-3.9
-32.6
Transportation Total
1,524.6
1,970.9
1,846.0
1,876.2
1,879.2
1,629.2
1,809.5
284.9
18.7
On-Road Vehicles
1,459.4
1.0
9.4
26.6
1,496.4
74.3
Passenger Cars
365.0
0.3
1.9
7.0
374.2
18.6
Light-Duty Trucks
654.0
0.5
4.2
13.0
671.8
33.3
Motorcycles
7.4
0.0
0.1
0.0
7.5
0.4
Buses
25.1
0.0
0.2
0.4
25.7
1.3
Medium- and Heavy-
Duty Trucks
407.8
0.1
3.0
6.3
417.1
20.7
Aircraft
154.1
0.0
1.3
0.0
155.4
7.7
Commercial Aviation
119.0
0.0
1.0
0.0
120.0
6.0
Military Aircraft
12.5
0.0
0.1
0.0
12.6
0.6
General Aviation
22.6
0.0
0.2
0.0
22.8
1.1
Ships and Boats
45.0
0.5
0.3
4.5
50.2
2.5
Rail
34.7
0.1
0.3
0.1
35.2
1.7
Pipelines6
64.2
0.0
0.0
0.0
64.2
3.2
Lubricants
8.0
0.0
0.0
0.0
8.0
0.4
Transportation Total
1,765.4
1.5
11.2
31.2
1,809.5
89.8
U.S. Non-Transportation Mobile GHG Emissions
Non-Transportation
Mobile7
166.9
224.2
201.4
207.0
210.9
200.6
205.5
38.7
23.2
Agricultural Equip.
44.7
52.5
41.4
41.1
40.9
39.8
37.6
-7.1
-15.9
Construction Equip.
50.2
78.3
66.9
70.0
72.2
68.0
71.2
21.0
41.8
Other
71.9
93.4
93.5
96.0
97.9
92.8
96.7
24.8
34.5
Non-Transportation +
Transportation Total
1,691.4
2,195.0
2,047.4
2,083.2
2,090.2
1,829.8
2,015.0
323.6
19.1
U.S. Non-Transportation Mobile GHG Emissions by Gas, 2021
Non-Transportation
Mobile7
198.9
1.1
5.6
0.0
205.5
10.2
Agricultural Equip.
36.5
0.1
1.0
0.0
37.6
1.9
Construction Equip.
69.3
0.2
1.7
0.0
71.2
3.5
Other
93.1
0.7
2.9
0.0
96.7
4.8
Non-Transportation +
Transportation Total
1,964.3
2.6
16.7
31.2
2,015.0
100.0
Change in GHG Emissions by Source: 1990-2021
I Light Duty Vehicles ¦ Medium-and Heavy-Duty Trucks BAircraft ~ Rail ¦ Non Transportation Mobile Sources
HAII Other Transportation Sources
¦ Ships and Boats
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021
Includes only C02 from natural gas used to power natural
gas pipelines; does not include emissions from electricity
use or non-C02 gases.
Note: non-transportation mobile source C02 emissions
estimates are presented here and in Annex 3.2 of the
Inventory for informational purposes,but these emissions
are officially accounted for in the industrial and commercial
sectors of the Inventory. See Annex 3.2 of the Inventory for
more information.
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2021 Fuel Consumption
Volume
(billion gallons unless
otherwise specified)
Energy (Tbtu)
C02 (Tg)
MOTOR GASOLINE
122.9
15,255.0
1,077.8
Transportation8
Passenger Cars
41.0
5,102.4
360.5
Light-Duty Trucks
70.6
8,774.3
619.9
Medium- and Heavy-Duty Trucks
3.1
387.7
27.4
Motorcycles
0.8
104.8
7.4
Buses
0.3
40.4
2.9
Recreational Boats
1.2
149.4
10.6
Non-Transportation Mobile9
Agricultural Equipment
0.1
16.2
1.1
Construction Equipment
0.4
46.8
3.3
Other Non-Transportation Mobile
5.3
633.1
44.6
DISTILLATE FUEL
59.6
8,263.2
612.5
Transportation8
Passenger Cars
0.3
36.6
2.7
Light-Duty Trucks
3.2
449.6
33.3
Buses
2.1
289.3
21.4
Medium- and Heavy-Duty Trucks
37.0
5,127.5
380.1
Recreational Boats
0.3
37.9
2.8
Ships and Non-Recreational Boats
0.8
105.1
7.8
Rail
3.1
434.3
32.2
Non-Transportation Mobile9
Agricultural Equipment
3.4
475.5
35.2
Construction Equipment
6.4
884.1
65.5
Other Non-Transportation Mobile
3.1
423.4
31.4
RESIDUAL FUEL OIL
2.1
318.1
23.9
Ships and Boats
2.1
318.1
23.9
JET FUEL
15.7
2,113.6
152.6
Commercial Aircraft
12.5
1,691.2
119.0
General Aviation Aircraft
2.0
265.4
21.1
Military Aircraft
1.2
157.0
12.5
AVIATION GASOLINE
0.2
21.6
1.5
General Aviation Aircraft
0.2
21.6
1.5
ELECTRICITY (Billion Kilowatt hours)
12.9
43.9
5.0
Transportation
Passenger Cars
4.5
15.5
1.8
Light-Duty Trucks
1.8
6.1
0.7
Buses
0.2
0.7
0.1
Rail
6.3
21.6
2.5
Volume
(billion gallons unless
otherwise specified)
Energy (Tbtu)
C02 (Tg)
NATURAL GAS (billion cubic feet)
1,234.8
1,280.5
67.7
Transportation
Passenger Cars
0.0
0.0
0.0
Light-Duty Trucks
0.2
0.2
0.0
Medium- and Heavy-Duty Trucks
2.2
2.2
0.1
Buses
13.4
13.9
0.7
Pipelines
1,170.5
1,213.8
64.2
Non-Transportation Mobile9
Agricultural Equipment
1.4
1.4
0.1
Construction Equipment
6.2
6.5
0.3
Other Non-Transportation Mobile
40.9
42.4
2.2
LPG
2.7
243.0
15.3
Transportation
Passenger Cars
0.0
0.0
0.0
Light-Duty Trucks
0.0
0.8
0.1
Medium- and Heavy-Duty Trucks
0.0
3.6
0.2
Buses
0.0
0.2
0.0
Non-Transportation Mobile9
Agricultural Equipment
0.0
0.0
0.0
Construction Equipment
0.0
2.4
0.2
Other Non-Transportation Mobile
2.6
235.9
14.8
LUBRICANTS
0.0
1.0
8.0
Total10
213.5
27,539.8
1,964.3
BIOFUELS"
14.7
1,319.7
91.5
Transportation
Biodiesel
1.7
218.0
16.1
Ethanol
13.0
1,101.7
75.4
8 Excludes contributions from biofuels.
9 Non-transportation mobile fuel consumption, energy, and C02 are estimated in part by the MOVES-Nonroad model (see www.epa.gov/
moves). Fuel consumption in MOVES-Nonroad is intended to reflect real-world usage and may include low-level ethanol blends. Note that
non-transportation mobile source C02 estimates are presented here and in Annex 3.2 of the Inventory for informational purposes, but
these emissions are officially accounted for in the industrial and commercial sectors of the Inventory and do not include emissions from
biofuels.
10 Total Volume is the sum of physical (billion) gallons of fuel; because natural gas volumes are reported as million cubic feet, natural gas
volumes are converted to billion gallons of gasoline equivalent for the Total Volume (billion gallons) sum in this table.
11 Biofuels are presented as line items for informational purposes only, in line with IPCC methodological guidance and UNFCCC reporting
obligations. Biofuel estimates only reflect transportation sources and do not include biofuels used in non-transportation mobile sources,
e.g., ethanol used in commercial or industrial applications. C02 emissions from the combustion of biofuels are not directly included in the
energy sector (which includes transportation sources) of the Inventory; instead, net carbon fluxes from changes in biogenic carbon reservoirs
are accounted in the estimates for Land Use, Land-Use Change, and Forestry in the Inventory. See page 4 for more information on the Inventory.
3
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Additional Information
Data Sources for This Document
The source for all data in this document is the Inventory of U.S. Greenhouse Gas Emissions and
Sinks 1990-2021 (EPA 2023). The U.S. Environmental Protection Agency prepares the inven-
tory annually to fulfill the U.S. commitment under the United Nations Framework Convention
on Climate Change (UNFCCC), using calculation methods that are consistent with guidelines
from the Intergovernmental Panel on Climate Change (IPCC). Complete information on the
inventory is available at: www.epa.gov/ghgemissions/inventory-us-greenhouse-gas-emissions-and-
sinks. The inventory methods and assumptions related to transportation and non-transportation
mobile sources are available in the main body of the Inventory as well as Annex 3.2 of the Inventory.
Inventory Definitions of Selected Transportation Categories12
Passenger Cars: automobiles used primarily to transport 12 people or less. In
2021, passenger cars traveled a total of 1,102,799 million vehicle miles.
Light-Duty Trucks: vehicles used primarily for transporting light-weight cargo
or which are equipped with special features such as four-wheel drive for off-road
operation. In the U.S., this category also includes many vehicles that primarily
transport passengers such as sport utility vehicles (SUVs) and minivans. The gross
vehicle weight rating (GVWR) normally ranges around 8,500 pounds or less.
GVWR is the maximum weight a vehicle is designed to carry when passengers,
fuel, cargo, and any other additions to the vehicle are accounted for. In 2021,
light-duty trucks traveled a total of 1,492,200 million vehicle miles.
Medium- and Heavy-Duty Trucks: vehicles with GVWR of more than around
8,500 pounds. In the Inventory, single unit trucks and combination trucks rep-
resent the medium- and heavy-duty truck category, including tractor-trailers and
box trucks used for freight transportation. In addition, this category includes
some vehicles that are not typically used for freight movement such as service
and utility trucks. In 2021, medium- and heavy-duty trucks traveled a total of
317,245 million vehicle miles.
Pipelines: systems that transport liquids, gases, or slurries through either
above or below ground pipes. In the Inventory, the pipelines category includes
emissions from the combustion of natural gas used to power pumps and other
distribution equipment, while leaks and other emission sources from pipelines
are assigned to the natural gas systems category.
Emissions Metrics
A teragram (Tg) is equal to 1 million metric tons.
Greenhouse gas (GHG) emissions are measured in this document in terms of teragrams of
"carbon dioxide equivalent" (C02 Eq); an "equivalent" refers to the Global Warming Potential
(GWP) of a greenhouse gas. GWP values are determined based on the chosen time horizon and
properties of the gas, such as its ability to absorb radiation and its atmospheric lifetime. C02 has
a GWP of "1"; all other greenhouse gases have GWP values relative to that of C02. For example,
methane (CH4) has a radiative forcing value or GWP of 28, which means that releasing one ton
of CH4 is equivalent to releasing 28 tons of C02.
The data in this document is based on the 100-year time horizon GWP values from the IPCC's
Fifth Assessment Report13, in accordance with UNFCCC reporting guidelines for national
GHG inventories. More information on greenhouse gases and GWP is available at:
www.epa .gov/ ghgemissions/overview-greenhouse-gase s.
12 The data used to estimate emissions for specific transportation categories may not directly align with the
Inventory's definition of the categories; both the data and Inventory definitions may also differ from EPA's
regulatory definitions for the same categories.
13 IPCC (2013) Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth
Assessment Report of the Intergovernmental Panel on Climate Change. [Stacker, T.F., D. Qin, G.K. Plattner,
M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press,
Cambridge, United Kingdom and New York, NY USA, 1535 pp.
4
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