Emissions measurement during roadside inspection of heavy-duty vehicles

Roadside inspection (RSI) plays a critical role in enforcing vehicle environmental performances compliance. Heavy-duty Diesel vehicles are significant contributors to nitrogen oxides (NOx) and particulate matter, posing risks to both the environment and human health. The European Commission's revision proposal of the roadworthiness legislation package introduces new test methods during technical inspections that account for NOx and particle number (PN) emissions, respectively aiming at detecting malfunctioning selective catalytic reduction (SCR) units and Diesel particulate filters (DPF). This study focusses on evaluating the advantages and limitations of various testing methods for RSI. For the first time, plume chasing, on-board diagnostics (OBD), and idle emissions tests are combined aiming to offer insights and recommendations for effective inspections. The study analysed emissions from over 30 heavy-duty vehicles, including Euro VI and earlier standards. Plume Chasing enabled effective identification of suspicious and high emitters. A detailed inspection of 29 vehicles found 33% malfunctioning, 26% tampered, and 20% chiptuned. Cases exhibiting severe SCR system failures were correctly identified by all methods. The OBD and idle test results were consistent in identifying vehicles without issues. The findings also highlighted challenges in accurately categorising high-emission vehicles due to factors like vehicles undergoing Diesel particulate filter regeneration or manipulation, for which the support confirmation from an authorised workshop was required. The results also show a great variability in emission manipulation types and their impacts. The study showcases the effectiveness of a multi-method inspection approach using plume chasing, idle emissions testing, and advanced OBD checks to identify heavy-duty vehicles with environmental performance issues. Plume chasing is suited for preliminary identification, while rapid idle tests detect severe failures in SCR systems efficiently, though OBD checks are necessary for comprehensive malfunction or manipulation detection. PN emissions testing enables the rapid identification of DPF failures or tampering and helps confirm DPF regeneration, preventing false inspection failures and demonstrating the effectiveness of filter retrofits. Combining and aligning measurement methodologies could improve emissions monitoring during inspections. This approach provides reliable pass/fail classifications, aiding regulatory authorities in addressing excessive emissions, thereby helping to reduce environmental impacts and improve public health.