In-Use Emissions Testing and Activity Profiles for On-Road Heavy-Duty Vehicles: Summary of 200 Heavy-Duty Vehicle Emissions Testing Program from the University of California, Riverside and West Virginia University

California’s on-road heavy-duty vehicles are major sources of harmful air pollutants, especially nitrogen oxides (NOx) which contribute to formation of ground level ozone and fine particulate matter. The South Coast Air Basin, which is in “extreme nonattainment” for national ozone standards, depends on systematic and rapid NOx emission reductions from heavy-duty vehicles. While new on-road heavy-duty vehicle models meet stringent emissions standards and even-tougher standards are coming by 2024, “in-use” vehicles can sometimes emit NOx and other pollutants at higher-than-design levels. This hinders progress toward attainment and understates emission inventories.

In this comprehensive, multi-year, four-phase program, the University of California, Riverside and West Virginia University collaborated with four industry and government agency cosponsors to test more than 200 heavy-duty vehicles, making it one of the world’s largest efforts to test in-use heavy-duty vehicle tailpipe emissions.

The program’s goals were to better characterize emissions of heavy-duty vehicles using conventional and alternative powertrains under real-world operating conditions, and to further understand causes for higher emissions, especially for NOx. The program provided insights for development and implementation of advanced technologies and expedited reductions needed for attainment of air quality standards.

Measured emission levels varied widely across different duty cycles, test methods, engine/fuel technologies, and vocations. Heavy-duty vehicles tested ranged from model year 2001 to 2019, and most exhibited elevated in-use emissions under operational conditions differ than certification cycle. New heavy-duty vehicle emission regulations have both included additional measures that address the gap between certification and in-use, and over various duty cycles. This extensive test program has also successfully provided new data to improve air quality modeling and planning. Program findings are informing follow-up work, policy decisions, and program development.