* The source used 2002 and 2005 MOVES data to update 2002-2007 figures. The change in model resulted in noticeable changes in highway emissions from 2001 to 2002 for various pollutants.
Figures refer to on-road or highway emission sources, which include vehicles used on roads for transportation of passengers or freight.
Citation formats
Road transportation nitrogen oxides emissions in the U.S. 1970-2024
Road vehicles in the United States emitted *** million tons of nitrogen oxides (NOx) in 2024. Emissions of NOx from road vehicles in the North American country have fallen considerably since the Clean Air Act was passed in 1970. Since then, increasingly stringent standards have resulted in NOx emissions from road vehicles to fall more than ** percent relative to 2002 levels.
Heavy-duty trucks are a major source of transportation emissions in the United States. In November 2020, the EPA announced the launch of the Clean Trucks Initiative in a bid to decrease NOx emissions from HDVs.
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Environmental Protection Agency. (April 28, 2025). Annual nitrogen oxides (NOx) emissions from road vehicles in the United States from 1970 to 2024 (in 1,000 tons) [Graph]. In ÌÇÐÄÆƽâ°æ. Retrieved July 14, 2026, from /statistics/1234938/road-transportation-nitrogen-oxide-emissions-us/
Environmental Protection Agency. "Annual nitrogen oxides (NOx) emissions from road vehicles in the United States from 1970 to 2024 (in 1,000 tons)." Chart. April 28, 2025. ÌÇÐÄÆƽâ°æ. Accessed July 14, 2026. /statistics/1234938/road-transportation-nitrogen-oxide-emissions-us/
Environmental Protection Agency. (2025). Annual nitrogen oxides (NOx) emissions from road vehicles in the United States from 1970 to 2024 (in 1,000 tons). ÌÇÐÄÆƽâ°æ. ÌÇÐÄÆƽâ°æ Inc.. Accessed: July 14, 2026. /statistics/1234938/road-transportation-nitrogen-oxide-emissions-us/
Environmental Protection Agency. "Annual Nitrogen Oxides (Nox) Emissions from Road Vehicles in The United States from 1970 to 2024 (in 1,000 Tons)." ÌÇÐÄÆƽâ°æ, ÌÇÐÄÆƽâ°æ Inc., 28 Apr 2025, /statistics/1234938/road-transportation-nitrogen-oxide-emissions-us/
Environmental Protection Agency, Annual nitrogen oxides (NOx) emissions from road vehicles in the United States from 1970 to 2024 (in 1,000 tons) ÌÇÐÄÆƽâ°æ, /statistics/1234938/road-transportation-nitrogen-oxide-emissions-us/ (last visited July 14, 2026)
Annual nitrogen oxides (NOx) emissions from road vehicles in the United States from 1970 to 2024 (in 1,000 tons) [Graph], Environmental Protection Agency, April 28, 2025. [Online]. Available: /statistics/1234938/road-transportation-nitrogen-oxide-emissions-us/
