Transportation Sector Emissions

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Sources of Transportation Emissions
Transportation Sector Emissions Trends
Reducing Emissions from Transportation

Sources of Transportation Emissions

The transportation sector includes the movement of people and goods by cars, trucks, trains, ships, airplanes, and other vehicles.

The majority of greenhouse gas emissions from transportation are carbon dioxide (CO₂) emissions resulting from the combustion of petroleum-based products, like gasoline and diesel fuel, in internal combustion engines.
The largest sources of transportation-related greenhouse gas emissions include passenger cars, medium- and heavy-duty trucks, and light-duty trucks, including sport utility vehicles, pickup trucks, and minivans. These sources account for over half of the emissions from the transportation sector.
The remaining greenhouse gas emissions from the transportation sector come from other modes of transportation, including commercial aircraft, ships, boats, and trains, as well as pipelines and lubricants. Indirect emissions from electricity are less than 1 percent of direct emissions.

Relatively small amounts of methane (CH₄) and nitrous oxide (N₂O) are emitted during fuel combustion. In addition, hydrofluorocarbon (HFC) emissions also occur from the transportation sector. These emissions result from the use of mobile air conditioners and refrigerated transport.

Transportation Sector Emissions Trends

In 2022, direct and indirect greenhouse gas emissions from transportation accounted for 29% of total U.S. greenhouse gas emissions, making it the third largest contributor of U.S. greenhouse gas emissions when considering indirect emissions from distributed electricity.
When considering only direct emissions, transportation is the largest contributor of U.S. greenhouse gas emissions (28%). From 1990 to 2022, total transportation emissions from fossil fuel combustion increased by 19%. From 2021 to 2022, emissions decreased by less than 1%.
The largest sources of transportation greenhouse gas emissions in 2022 were light-duty trucks, which include sport utility vehicles, pickup trucks, and minivans (37%); medium- and heavy-duty trucks (23%); passenger cars (20%); commercial aircraft (7%); other aircraft (2%); pipelines (4%); ships and boats (3%); and rail (2%).
In terms of the overall trend, from 1990 to 2022, total transportation emissions have increased due, in large part, to increased demand for travel. The number of vehicle miles traveled (VMT) by light-duty motor vehicles (passenger cars and light-duty trucks) increased by 47% from 1990 to 2022, as a result of a confluence of factors including population growth, economic growth, urban sprawl, and periods of low fuel prices.
Between 1990 and 2004, average fuel economy among new vehicles sold annually declined, as sales of light-duty trucks increased. Starting in 2005, average new vehicle fuel economy began to increase, while light-duty VMT grew only modestly for much of the period. Average new vehicle fuel economy has improved almost every year since 2005, slowing the rate of increase of CO₂ emissions.

Learn more about Greenhouse Gas Emissions from Transportation.

Reducing Emissions from Transportation

There are a variety of opportunities to reduce greenhouse gas emissions associated with transportation. The table shown below categorizes these opportunities and provides examples. For a more comprehensive list, see Chapter 10 of the Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change.¹

Examples of Reduction Opportunities in the Transportation Sector
Type	How Emissions Are Reduced	Examples
Fuel Switching	Using fuels that emit less CO₂ than fuels currently being used. Alternative sources can include biofuels; hydrogen; electricity from renewable sources, such as wind and solar; or fossil fuels that are less CO₂-intensive than the fuels that they replace. Learn more about Green Vehicles and Alternative and Renewable Fuels.	Using public buses that are powered by renewable fuels, electricity, or compressed natural gas rather than conventional gasoline or diesel. Using electric, plug-in hybrid electric, or hydrogen fuel cell vehicles. Using renewable fuels such as low-carbon biofuels.
Improving Fuel Efficiency with Advanced Design, Materials, and Technologies	Using advanced technologies, design, and materials to develop more fuel-efficient vehicles. Learn about EPA's vehicle greenhouse gas rules.	Developing advanced vehicle technologies such as hybrid vehicles and electric vehicles, that can store energy from braking and use it for power later. Reducing the weight of materials used to build vehicles. Reducing the aerodynamic resistance of vehicles through better shape design.
Improving Operating Practices	Adopting practices that minimize fuel use. Improving driving practices and vehicle maintenance. Learn about how the freight transportation industry can reduce emissions through EPA's SmartWay Program.	Reducing the average taxi time for aircraft. Driving sensibly (avoiding rapid acceleration and braking, observing the speed limit). Reducing engine-idling. Improved voyage planning for ships, such as through improved weather routing, to increase fuel efficiency.
Reducing Travel Demand	Employing urban planning to reduce the number of miles that people drive each day. Reducing the need for driving through travel efficiency measures such as commuter, biking, and pedestrian programs. Learn about EPA's Smart Growth Program.	Building public transportation, sidewalks, and bike paths to increase lower-emission transportation choices. Zoning for mixed use areas, so that residences, schools, stores, and businesses are close together, reducing the need for driving.

References

IPCC, 2022: Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [P.R. Shukla, J. Skea, R. Slade, A. Al Khourdajie, R. van Diemen, D. McCollum, M. Pathak, S. Some, P. Vyas, R. Fradera, M. Belkacemi, A. Hasija, G. Lisboa, S. Luz, J. Malley, (eds.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA. doi: 10.1017/9781009157926

An Explanation of Units

A million metric tons of CO₂: What does that mean?

A million metric tons equals about 2.2 billion pounds, or 1 trillion grams. For comparison, a small car is likely to weigh a little more than 1 metric ton. Thus, a million metric tons are roughly the same mass as 1 million small cars.

The U.S. GHG Inventory uses metric units for consistency and comparability with other countries. For reference, a metric ton is slightly more (approximately 10%) than a U.S. "short" ton.

Greenhouse gas emissions are often measured in carbon dioxide (CO₂) equivalent. To convert emissions of a gas into CO₂ equivalent, its emissions are multiplied by the gas's Global Warming Potential (GWP). The GWP takes into account the fact that many gases are more effective at warming Earth than CO₂, per unit mass.

The GWP values appearing in the Overview of Greenhouse Gases and Sources of Greenhouse Gas web pages reflect the values used in the U.S. GHG Inventory, which are drawn from the IPCC's Fifth Assessment Report (AR5). For further discussion of GWPs and an estimate of greenhouse gas emissions using updated GWPs, see Annex 6 of the U.S. GHG Inventory and the IPCC's discussion on GWPs (pdf) (13.9 MB).