UN R145 and UN R173 establish optional ISOFIX installation for vehicles of category M₂ and M₃. ISOFIX seating positions require compatibility with specific Child Restraint Fixture volumes and lower isofix forward strength of 8kN. I-Size seating positions require minimum 440mm distance between adjacent positions, compatibility with ISO/F2X and ISO/R2, and additional support leg strength testing. The document proposes allowing labels on bus windows and removing marking requirements for M₂ and M₃ from UN R145.