Final status report on development of a new UN Global Technical Regulation addressing particle matter (PM) and particle number (PN) emissions from heavy-duty vehicle brake systems. The GTR introduces brake emissions groups based on design and performance characteristics, establishes test parameters for disc and drum brakes across five diameter groups, defines the World Harmonized Heavy-Duty Brake Cycle (WHBC) comprising 246 brake events over 5:39 hours, specifies brake dynamometer hardware requirements with enclosure dimensions of 1950 mm length, 1000 mm height, and 700 mm depth, requires PM10 and PM2.5 gravimetric measurement and particle number counting, and prescribes a friction braking share coefficient (c-factor) of 1 pending availability of additional data. A preliminary interlaboratory study confirms test cycle reproducibility and particle measurement repeatability, with recommendations to specify fixed enclosure and duct dimensions for improved cross-laboratory consistency.