Proposal to amend UN R49 to approve the use of hydrogen dual-fuel as a fuel in type approval of emissions for heavy-duty vehicles. The amendments introduce new requirements for measuring instruments such as FT-IR and QCL-IR, add symbols and specifications for hydrogen-fuelled engines specifying that only Type 1A hydrogen fuel is applicable, amend emission calculation formulas for ETC/ESC and WHDC test procedures, add new HO direct measurement methods for NOx wet correction calculation, and add declaration formats for FT-IR and QCL-IR approval.