Proposal to establish a globally harmonised laboratory methodology for measuring brake particulate matter (PM) and particle number (PN) emissions from heavy-duty vehicles, including trucks and buses, using a Worldwide Harmonized Heavy Duty Vehicles Brake Cycle (WHBC) and brake dynamometer testing. The GTR specifies test system requirements, including brake enclosure design, sampling tunnel specifications, climatic conditioning with cooling air temperature maintained at 23°C±2°C and relative humidity at 50%±5%, cooling airflow at 2500 Nm/h±5%, test preparation procedures, brake bedding with six repetitions of the WHBC followed by emissions measurement during one WHBC cycle, requirements for PM10, PM2.5, TPN10, and SPN10 measurement systems, brake temperature measurement using embedded thermocouples, calibration and validation procedures, and reporting of emission factors. The regulation applies to vehicles of categories M₂, M₃, N₂, N₃ [and O₃, O₄] with friction braking systems.