On January 21, 2020, the U.S. Environmental Protection Agency (EPA) published an advanced notice of proposed rulemaking (ANPR) for heavy-duty engines as part of its Cleaner Trucks Initiative. The ANPR seeks comments on EPA’s plans for a new rulemaking that would set out new emission standards for oxides of nitrogen (NOx) and other pollutants for highway heavy-duty engines. Also under consideration are efforts to streamline or otherwise change certification procedures, with the stated goal of reducing costs for engine manufacturers. EPA covers a broad array of topics: lowering NOx emission standards, changing test procedures and test cycles to ensure emission reductions occur in the real world, transitioning to electrification, the impact of fuel types on after-treatment durability, potentially lengthening useful life and warranty periods, and cybersecurity, among many others. EPA is accepting comments for 30 days, until February 20, 2020. EPA has stated that it hopes to act exceptionally quickly and issue a proposed rule by late spring, with the goal of issuing a final rule as early as fall 2020.