Researchers from Shenzhen Polytechnic University, the University of California, Riverside, and Tsinghua University evaluated real-world emissions from China V and China VI heavy-duty diesel trucks using portable emissions measurement systems (PEMS). The study found that compliant China VI trucks can significantly reduce NOx and particle number (PN) emissions, while some vehicles still showed excessive emissions under real driving conditions, highlighting the need for stronger in-use supervision.
The team published their study in Communications in Transportation Research ( https://doi.org/10.26599/COMMTR.2026.9640033 ).
"We wanted to understand whether the stricter China VI regulations can truly deliver cleaner emissions under actual driving conditions," says Dr. Weixia Li from Shenzhen Polytechnic University. "Real-road testing is critical because vehicle performance in laboratories may differ substantially from real-world operations."
Real-road testing reveals mixed emission performance
Heavy-duty diesel trucks are major contributors to nitrogen oxides (NOx) and particulate matter (PM) emissions in the transportation sector. To reduce these pollutants, China implemented the China VI heavy-duty vehicle emission standard in 2021, introducing stricter NOx limits, particle number (PN) regulations, and mandatory portable emissions measurement systems (PEMS) testing.
In the study, the researchers conducted real-road emission tests on 24 heavy-duty diesel trucks, including both China V and China VI vehicles from different manufacturers. The team measured NOx and PN emissions under various driving conditions.
The results showed that compliant China VI vehicles reduced PN and NOx emissions by 51.5% and 59.6%, respectively, compared with China V vehicles. However, some China VI trucks still produced unexpectedly high emissions under real-road conditions. Among the tested vehicles, 28.6% exceeded PN limits and 23.8% exceeded NOx limits.
"Some non-compliant China VI vehicles even emitted more pollutants than older China V trucks," says Dr. Li. "This suggests that stricter standards alone are not enough without effective in-use monitoring and maintenance."
SCR and EGR systems play important roles
The study also examined how after-treatment systems performed under different operating conditions. The researchers found that SCR systems achieved NOx reduction efficiencies ranging from 76.6% to 96.8%, although performance decreased during low-speed driving possibly because of lower exhaust temperatures. In addition, vehicles equipped with EGR systems generally showed lower NOx emissions across most driving conditions, indicating that EGR can effectively complement SCR-based emission control strategies.
"Our findings highlight the importance of maintaining stable after-treatment performance under complex driving conditions," says Dr. Li. "Future regulations should place greater emphasis on real-driving compliance and low-speed emission control." The researchers believe the study can support future emission regulations, cleaner freight transportation systems, and more effective real-road emission supervision.
About Communications in Transportation Research
Communications in Transportation Research was launched in 2021, with academic support provided by Tsinghua University and China Intelligent Transportation Systems Association. The Editors-in-Chief are Professor Xiaobo Qu, a member of the Academia Europaea from Tsinghua University, and Professor Xiaopeng (Shaw) Li from University of Wisconsin–Madison. The journal mainly publishes high-quality, original research and review articles that are of significant importance to emerging transportation systems, aiming to serve as an international platform for showcasing and exchanging innovative achievements in transportation and related fields, fostering academic exchange and development between China and the global community.
It has been indexed in SCIE, SSCI, Ei Compendex, Scopus, CSTPCD, CSCD, OAJ, DOAJ, TRID and other databases. It was selected as Q1 Top Journal in the Engineering and Technology category of the Chinese Academy of Sciences (CAS) Journal Ranking List. In 2022, it was selected as a High-Starting-Point new journal project of the "China Science and Technology Journal Excellence Action Plan". In 2024, it was selected as the Support the Development Project of "High-Level International Scientific and Technological Journals". The same year, it was also chosen as an English Journal Tier Project of the "China Science and Technology Journal Excellence Action Plan PhaseⅡ". In 2024, it received the first impact factor (2023 IF) of 12.5, ranking Top1 (1/58, Q1) among all journals in "TRANSPORTATION" category. In 2026, its 2025 IF was announced as 12.7, maintaining the Top1 position (1/66, Q1) in the same category.
From Volume 6 (2026), Communications in Transportation Research will be published by Tsinghua University Press on the SciOpen platform with the official journal website at https://www.sciopen.com/journal/2097-5023 . We kindly request that all new manuscript submissions be made through the journal's submission system at https://mc03.manuscriptcentral.com/commtr
