In late 1980 the U.S. Environmental Protection Agency (EPA), as part of its rulemaking in establishing emission standards for heavy-duty vehicles called for in the Clean Air Act, as amended in 1977 (42 USC 7401 et seq.), requested that the National Research Council study the technological feasibility of meeting a more stringent standard for nitrogen oxides (NOx) emissions by 1986. The Assembly of Engineering established the Motor Vehicle Nitrogen Oxides Standard Committee to carry out the requested study. Heavy-duty vehicles are extremely varied in size, operating conditions, and vehicle type; the category includes trucks, buses, large vans, and recreational vehicles. This report focuses on the impact of emission control technologies on the cost, efficiency, and performance of heavy-duty engine vehicles and their impact on other potentially hazardous engine emissions. The committee sought to provide an independent analysis of the scientific, technical, and cost issues raised by NOx emission controls for heavy-duty vehicles of model year 1986. The committee noted several policy questions that arose from the technical findings in this study; these questions should be considered in a rulemaking procedure, but in the committee's judgment their answers require policy decisions beyond the scope of the committee's charge.