Under the Clean Air Act, CARB is responsible for developing statewide programs and strategies to reduce smog-forming and toxic pollutants emitted from mobile sources. Heavy-duty diesel vehicles greater than 14,000 pounds are major contributors to California’s air quality challenges. These vehicles still contribute the majority of on-road NOx and PM 2.5 emissions, despite significant efforts by CARB over the last 40 years to reduce NOx and PM emissions from this sector. (more..)