from the French “Groupe de Rapporteurs”; signifies any of the permanent working parties subsidiary to WP.29 (e.g. on noise, lighting, pollution and energy, passive safety, etc.)
GRRF
Working Party on Brakes and Running Gear (cf French: Groupe de Rapporteurs sur le Roulement et le Freinage)
GRSP
Working Party on Passive Safety (cf French: Groupe de Rapporteurs sur la Sécurité Passive)