Benefits of adopting California medium- and heavy-duty vehicle regulations under Clean Air Act Section 177

In recent years, the State of California has adopted key regulations to reduce greenhouse gas and criteria pollutant emissions from medium- and heavy-duty vehicles. The Advanced Clean Trucks (ACT) rule requires the sale of at least 30% zero-emission trucks by 2030; the HDV Omnibus rule requires a 90% reduction in NOx emissions from Model Year 2027 engines; and the California Phase 2 greenhouse gas rule sets standards to improve the efficiency of tractor-trailers. Section 177 of the U.S. Clean Air Act (CAA) allows U.S. states to adopt California regulations that meet or exceed federal standards provided two conditions are met: (1) such standards are identical to California standards and (2) the state adopts such standards at least two years before commencement of any model year granted a waiver from federal requirements by the U.S. Environmental Protection Agency Administrator. This year, several Section 177 states have proposed regulations to adopt California’s ACT rule.1 These states are members of a group of fifteen states and the District of Columbia who signed a Memorandum of Understanding in 2020 to adopt market-enabling mechanisms and to consider regulatory approaches to spur the market for zero emission medium- and heavy-duty vehicles. o understand the impact these regulations could have on medium- and heavy-duty vehicle emissions in in these states and the District of Colombia, the ICCT commissioned Sonoma Technology, Inc. (STI) to estimate the cumulative avoided nitrogen oxides (NOx), fine particulate matter (PM2.5) and well-to-wheel carbon dioxide equivalent (WTW CO2e) emission reductions beginning in 2025.