Working draft proposal for a 04 series of amendments to UN R51, establishing specifications for sound emission measurement and limits. The regulation sets sound level limits varying by vehicle category, mass, and power output, ranging from 68 to 79 dB(A). It includes methods for measuring vehicle sound outdoors and indoors, specifications for test conditions including vehicle mass, speed, and acceleration, requirements for sound reduction systems and exhaust silencing, transitional provisions, and Real Driving Additional Sound Emission Provisions (RD-ASEP) for M₁ and N₁ vehicles with specific exemptions based on engine capacity, payload, mass, and power-to-mass ratio.

Comments on draft UN R51.04 addressing various editorial and technical issues in Annexes 3, 6, 7, 8, and 9, including:

• Corrections to tyre conditioning text,
• Clarification of test speed tolerance,
• Changes to figure captions from ‘microphone point’ to ‘microphone position’,
• Corrections to formulas for anchor point parameters,
• Relocation of test report paragraph,
• Removal of unnecessary asterisk and footnote regarding ISO 10844 certification dates,
• Clarification of limit value specifications,
• Vehicle scope definitions,
• Definition necessity review,
• Incorporation of JASIC proposals for compliance assessment cases,
• Corrections to appendix references,
• Parameter reporting specifications,
• Adjustments to virtual engine speed calculations for hybrid electric vehicles.

The Working Party on Noise and Tyres held its eighty-fourth session from 2-4 September 2026 in Geneva. GRBP adopted a draft new Supplement to the 02 series and a draft new Supplement to the 04 series of amendments to UN R117, and agreed to submit these to WP.29 and AC.1 for consideration and vote at their March 2027 sessions. GRBP adopted the content of a proposal for a new supplement to UN R64 and agreed to postpone submission to WP.29 until further notice. GRBP adopted revised Terms of Reference for the IWG on Real Driving-Additional Sound Emission Provisions with extended mandate until February 2028.

Proposal to simplify the RD-ASEP SEM assessment method for electric vehicles using the Supplement 11 to UN R51 slope assessment approach, limit factor x between 0.10 and 0.95, apply AVAS as a uniform 66 dB(A) maximum up to 50 km/h, and replace the existing SEM-AVAS term with this revised strategy. The tyre rolling sound curve, acceleration term from UN R51.03 Supplement 11, and AVAS term aligned with UN R138 are applied, while no other SEM parts are used.

Notes from the 19th meeting of the Task Force Data Analysis, a sub-group of IWG RD-ASEP, scheduled for 2 November 2026. The meeting will discuss amendments to RD-ASEP including treatment of AVAS as a component, consideration of L_DYN definitions, a simplified assessment method for electric vehicles, rounding procedures, and temperature correction. Open items for TF-Editing include independence of test points, gear-shifting and HEV engine operation, dynamic jump, and low load cruising acceleration determination.

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.

Draft agenda for the nineteenth meeting of the Task Force Data Analysis, a subgroup to IWG RD-ASEP, scheduled for 2 November 2026. The meeting will address continued discussion on amendments to RD-ASEP, including consideration of LDYN definition, simplified assessment methods for EV, rounding procedures, and temperature correction. Open items concern independence of RD-ASEP test points correlation assessment, gearshifting and HEV engine operation, dynamic jump, and low load cruising acceleration determination.

Proposal to simplify the RD-ASEP Sound Emission Model for electric vehicles by using the tyre rolling sound curve with factor x set to 1.00 and slopes from the SEM parameter table, adopting the acceleration term from UN R51.03 Supplement 11, aligning the AVAS term with UN R138 as a uniform value of 66 dB(A) maximum sound up to 50 km/h, limiting factor between 0.10 and 0.90, using LDYN as specified, and replacing the existing SEM-AVAS term with the new strategy.

Agenda for the 16th session of IG-ASEP scheduled for 14-15 October 2026 as a virtual meeting. The session will include welcome remarks, introduction of participants, adoption of the draft agenda, review of minutes from the 15th session, review of Terms of Reference from GRBP 84th Session, and discussion of UN R51 matters including reports from the Data Analysis Task Force, review of the issues list, review of draft text R51.04, review of report to GRBP, and status report on RD-ASEP Alternatives. The next meeting is scheduled for 2 February 2027 in Geneva.

Presentation comparing results of Switzerland’s NExUS study on electric vehicles and internal combustion engine vehicles with RD-ASEP Sound Expectation Model predictions. NExUS study objective was to compare EVs with ICE vehicles of the same consumer segment to better understand EV modelling. Key findings show overall sound levels of EVs and modern ICEs are close under constant speed, while ICE sound is higher under low-speed acceleration. RD-ASEP SEM predictions align closely with NExUS measurements for both accelerated and constant speed conditions.

Document presents comparison of UN R51.03 ASEP, UN R51.04 RD-ASEP, and an updated ASEP alternative concept. It outlines improvements including explicit testing of all conditions to reduce test detection schemes, expanded vehicle speed range to 1-100 km/h, random test point evaluation, and extension to part load conditions. Main open topics include tyre model stability, technology and model temperature correction, application and uncertainties, and criteria and judgement safeguards. Document identifies quick wins through clarification that all modes must be tested and suggests main improvements can be realized through an updated, simple ASEP with part load testing capabilities.

Presentation on the Nord2000 noise model used in Sweden for road traffic noise mapping. Nord2000 uses five vehicle categories described by weight and number of axles, with 1/3 octave band frequency resolution from 25 to 10000 Hz. Two sources per vehicle category represent rolling and propulsion mechanisms. The model includes surface corrections based on Swedish CPX measurements, horizontal and vertical directivity patterns, and methods for deriving source sound power levels from field measurements using the propagation model with assumed omnidirectional sources.

Study identifying and prioritizing road traffic parameters that most strongly influence linear acoustic power levels and noise exposure using the European regulatory method CNOSSOS-FR in the Hauts-de-Seine department. Sensitivity calculations applied to 25 of 36 municipalities using E5 parameters, with population exposure counted using the median method. Analysis examines hourly traffic composition, pavement data from Renault sensors collected June 2024 to May 2026, and average speed data from departmental and national sources.

Policy briefing on road traffic noise as a health hazard and the opportunity for electric vehicles to reduce environmental noise pollution. Documents health impacts including hearing loss, cardiovascular disease, cognitive impairment, and sleep disruption, with particular vulnerability for infants, children, seniors, and people with pre-existing conditions. Addresses enhanced exterior sound systems in EVs that replicate combustion engine noise, undermining noise reduction benefits. Recommends regulating acoustic vehicle alerting systems for pedestrian safety while prohibiting sounds beyond public safety requirements, and prioritizing public health over commercial preferences.

Overview of rounding principles for calculations in models where results are used for further calculation. Recommends carrying full precision until the end and applying rounding only to final output. Identifies Round Half to Even as standard for modeling and statistics, and Round Half Up as used in UN Regulations. Advises matching output precision to input data uncertainty and not reporting more precision than input data warrants.

Task Force Data Analysis provides input to the Editing Task Force on three items. For vehicles with single gear ratios, remove brackets from text restricting acceleration to no more than 2.0 m/s and continue with adopted text for UN R51.04. Restructure Annex 7 paragraph 4.4. into subparagraphs for clarity. Rework paragraph 3.6.1. to define reference acceleration with v-t-e ratio and specify procedures for determining maximum reference acceleration. Add specification to factor x determination to prevent extreme results and harmonize its representation as either percentage or decimal value.

Agenda for the 23rd session of the Task Force on Vehicles Sound on 20 October 2026. The session will cover adoption of the agenda and report of the 22nd session, exchange of information on national and international requirements including presentations on quiet communities and noise sensitivity analysis, cross-matrix comparison of sound traffic modelling approaches with presentations on noise modelling and CNOSSOS-FR parameters, any other business, and arrangement of the next meeting in February 2027.

Meeting minutes from the GRBP Informal Group RD-ASEP held August 31–September 2026 in Berlin, Germany. The group reviewed the status report to GRBP, an issues list, and draft text for UN R51.04. OICA presented a document on the sensitivity of RD-ASEP results and difficulty of assessing worst case vehicle. The Secretary presented updated terms of reference to GRBP for approval. Experts are requested to submit all documents a minimum of 7 days prior to any IWG meeting date.