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In 2020 the U.S. South-Central Region (Texas, New Mexico, Oklahoma, Arkansas, and Louisiana) had the highest share (54.5%) of registered heavy-duty diesel trucks equipped with selective catalytic reduction (SCR) and particulate matter (PM) control technologies. SCR reduces emissions of nitrogen oxides (NOx). EPA regulations have required all heavy-duty diesel trucks since model year 2010 to have these emission reduction technologies. Three regions—South-Central, Great Lakes (53.6%), and Mid-Atlantic (52.3%) surpassed the national average of 49%.

Share of Heavy-Duty Diesel Trucks in Operation Equipped with SCR and PM-reduction Technologies by Region, 2020