EPA proposed amendments to its 2023 Heavy-Duty Engine Rule, which had set a 650,000-mile, 11-year useful-life period (the period during which an engine’s certified emissions standards must be met) and a 450,000-mile, 10-year emissions-warranty period (obliging manufacturers to pay for emissions-related component parts that fail) for diesel nitrogen oxides controls—structured so manufacturers could either absorb those durability costs, or shift more of their fleet toward electric trucks, busses, and tractors to avoid them. EPA's proposal would cut the warranty period to 100,000 miles and 5 years, delay implementation of its longer useful-life standard from 2027 to 2030, and expand related compliance flexibilities for diesel engines. Together, these changes substantially lower the cost of continuing to build and sell heavy-duty diesel vehicles, relative to the 2023 baseline.