Proposal to amend UN Regulation No. 51 concerning approval of motor vehicles with regard to sound emissions. The document provides comprehensive specifications for noise measurement methods and limits for vehicles of categories M and N, including:

• Sound level limits based on vehicle category and power-to-mass ratio,
• Measurement procedures for both moving and stationary vehicles,
• Definitions of terms and test conditions,
• Specifications for silencing systems and enhanced exterior sound systems,
• Requirements for Real Driving Additional Sound Emission Provisions (RD-ASEP) applicable to categories M₁ and N₁,
• Transitional provisions allowing acceptance of type approvals granted to the preceding 03 series of amendments until a specified date.