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.

Proposal to establish revised terms of reference for the IWG RD-ASEP covering vehicles of categories M₁, N₁, and L₃. The group shall modify current regulations to mandate revised RD-ASEP, update Annex 9, delete Annex 7 and update relevant paragraphs in the main body and Annex 3 of UN R51, develop limit curves for different riding situations in UN R41-05, consider relevant transitional provisions, and develop coordination between UN R51 and UN R138. The IWG shall be chaired by Germany with OICA as Secretary for M/N categories and IMMA for L category, and shall present a working document for M₁ and N₁ vehicles by February 2028.

Proposal to amend UN Regulation No. 51 on the noise of M and N category vehicles, introducing comprehensive provisions for measuring and limiting sound emissions. The proposal establishes testing methods for vehicles in motion and at rest, defines sound level limits by vehicle category and power characteristics, and introduces Real Driving Additional Sound Emission Provisions (RD-ASEP) for M1 and N1 vehicles to ensure compliance during typical on-road driving conditions representative of urban and suburban traffic. Transitional provisions permit Contracting Parties to continue approving vehicles under preceding series until a specified date.

Report from the Task Force Data Analysis to the Informal Working Group on Real Driving Sound Emissions and Performance (IWG RD-ASEP) covering several technical matters: clarification on restrictions in UN R51 supplement 11 to avoid high noise levels for single-gear vehicles; restructuring of control range specifications in Annex 7; redefinition of maximum reference acceleration for the sound emission model; discretization of factor x determination with consideration of rounding procedures; clarification of AVAS sound level requirements distinguishing between whole-vehicle and component-level interpretations; and temperature correction application for the sound emission model. Further work topics include indoor testing, EV model simplification, and slope considerations.

The agenda includes a review of Terms of Reference from GRBP 78th Session (GRBP-78-13), report of Data Analysis Task Force, review of issues list, review of draft text, and discussion of UN R51 matters. Dates and locations of 2027 meetings will be determined.

Document presents technical challenges to defining retrofit kit types for electric conversion and approval processes. Identifies that retrofit kit type perimeter depends on the regulation considered, with different requirements across UN R10, R13, R100, R85, R138, WLTP, R79, R39, R51, R89, R121, and R122. Presents testing challenges at vehicle, component, and EPRS levels, noting that testing a kit type not installed on a vehicle is impossible to account for all impacts on the vehicle.

Proposal to amend Annex 7, paragraph 2.3.1 to explicitly frame the area of valid values for factor x, requiring that the factor x determined by measurements shall always be at least 0.10 and not exceed the values provided by the parameter table in Appendix 2 to that Annex. The document explains that factor x is used to split constant speed test results energetically into tyre rolling sound and power train mechanic references, and that measurement variations can cause significant variability in calculated values, particularly when factor x exceeds 0.90.

Summary of the Task Force Data Analysis meeting held 29 September 2026. The meeting discussed amendments to factor x for improved model robustness, consideration on LDYN with amendments on factor x, and considerations on the AVAS term to match UN R138. Proposals to the TF-Editing were discussed based on draft UN R51.04, including input from Germany. The Editing TF raised a question regarding the phrase “but no more than 2.0 m/s” in para. 3.1.2.1.4.3 concerning vehicles with only one gear ratio, which was included in Supplement 11 to UN R51.03 to prevent unrealistic kp values. TF-DA suggested proceeding with the adopted text as is.

Proposal to replace the current logarithmic function with a segmented function that linearizes the curve in the unstable area near the clipping boundary. The new formulation uses a tangent line to the logarithmic curve below the tangency point and clips to a minimum value of 10 dB. Two parameters define the tangency and clipping conditions: clipping value of 10 dB and slope of 5 dB per unit. The detailed formulation provides the mathematical definitions of the logarithmic function, the linearized segment, helper variables, and constraints including tangency and asymptote conditions.

Agenda for the 18th meeting of the Task Force Data Analysis, a sub-group to IWG RD-ASEP. The meeting will review and adopt the agenda, discuss the meeting schedule for November and December 2026, continue discussion on necessary amendments to RD-ASEP including LDYN definition, AVAS term alignment with UN R138, temperature correction, indoor testing, simplified EV model with integrated AVAS approach and Supplement 11 amendments, and slopes and parameter table settings. The meeting will review proposals to the TF-Editing and decisions for the next meeting.

Proposal to restructure para. 4.4. by dividing it into paras. 4.4.1. through 4.4.8., add a new para. 4.4.7. permitting acceptance of measurements of RD-ASEP leading to operation conditions outside the control range when agreed by the manufacturer and authority, modify the heading of para. 3.6.1. to reference a selected reference v-t-e ratio, update references to v-t-e ratio terminology throughout para. 3.6.1.1., add a provision that negative acceleration values be set to zero in para. 4.5.4.1., restructure para. 2.2.1.2. by renumbering into paras. 2.2.1.2.1. and 2.2.1.2.2., and modify the reference vehicle speed parameter designation from vTEST to vPP,CRS.

Considerations by TF Data Analysis on revising the AVAS term in the RD-ASEP Sound Expectation Model to align with UN R138.02 specifications for electric and hybrid electric vehicles. The document presents two options: Option 1 implements UN R138.02 specifications for constant speed conditions; Option 2 extends Option 1 with an additional term to reflect paragraph 6.2.8 requirements for accelerated conditions. A revised AVAS term formula is proposed applicable only for vehicle speeds up to 50 km/h.

Document presents considerations on amendments to the RD-ASEP Sound Expectation Model SEM concerning calculation of the dynamic base and dynamic load addon. The dynamic sound increase of a vehicle is covered by a dynamic term aggregating all dynamics. A minimum threshold is proposed to be specified as max(0.25; ΔL_dyn) to ensure the function does not become zero or negative due to measurement uncertainties. The value 0.25 is selected to deliver comparable results as the current 10 dB minimum dynamic specification. In combination with a restriction of factor x to an area of 10 to 90 for ICE, the model becomes very robust with fluent transients and no unsteady steps.

Proposal to amend Annex 7, para. 2.3.1 to constrain the factor x determined by discrete coast-down measurement to a minimum of 10 and a maximum of 90 for internal combustion engine and hybrid electric vehicles, or 95 for electric vehicles, ensuring the Sound Expectation Model remains robust against measurement variations in tyre rolling sound and powertrain mechanic sound splitting.

Agenda for the Task Force Data Analysis meeting of 29 September 2026. Discussion topics include amendments to factor x for improved model robustness, consideration on LDYN with amendments on factor x, considerations on the AVAS term to match UN R138, amendments to reference acceleration, temperature correction, indoor testing, simplified model for electric vehicles with integrated AVAS approach and amendments from Supplement 11, and considerations on slopes in the RD-ASEP model. The Task Force will prepare proposals for wording on issues identified in the editing task force list and address a clarification request regarding the phrase ‘but no more than 2.0 m/s’ in para. 3.1.2.1.4.3. concerning vehicles with only one gear ratio.

Document presents suggested revisions to test procedures in Annex 7 and Annex 7 Appendix 1:

• Renumber para. 4.4. into paras. 4.4.1. through 4.4.8. to structure target operation conditions,
• Insert new para. 4.4.7. to permit acceptance of measurement runs outside the control range when agreed by manufacturer and authority,
• Modify para. 3.6.1.1. to define maximum reference acceleration for a selected reference v-t-e ratio and clarify determination procedures,
• Add provision that in case calculated acceleration is negative, the value is set to zero,
• Restructure para. 2.2.1.2. to introduce subsections 2.2.1.2.1. and 2.2.1.2.2. for parameters from acceleration and constant speed tests respectively, and modify parameter definitions including use of vPP,CRS instead of fixed 50 km/h reference speed.

Considerations by TF-Data Analysis regarding tyre slopes, power train slopes, and part load model for the RD-ASEP Sound Expectation Model. Tyre slopes α = 40 and β = 20 are confirmed as appropriate for UN R117 approved tyres. Power train slopes are confirmed as well-framed to normal vehicle behaviour and consistent with Annex 7 ASEP Slope-Assessment principles. For part load model, the function is confirmed for ICE vehicles and HEV in ICE mode, while for EVs and HEVs in EV mode the part load area may require reworking, but the part load model should be applied uniformly to all vehicle techniques.

Document presents considerations on amendments to the RD-ASEP Sound Expectation Model SEM. A simplified approach for electric vehicles is proposed based on Supplement 11 to UN R51.03, using a tyre rolling sound curve with slopes identical to internal combustion engine and hybrid electric vehicles, plus an acceleration term from UN R51.03 Supplement 11 as an additional term, and the AVAS term from Option 1, without other parts of the SEM.

Document presents considerations on revising the AVAS term in the RD-ASEP Sound Expectation Model to align with UN R138.02 specifications for electric and hybrid electric vehicles. Two options are discussed: Option 1 implements only constant speed specifications from UN R138.02, while Option 2 extends this with an additional term to reflect interpretation of paragraph 6.2.8 for accelerated conditions. A revised AVAS term formula applicable for vehicle speeds up to 50 km/h is proposed.

Proposal to amend the determination of reference acceleration aREF by introducing a theoretical calculation formula based on PMR, rated engine speed S, and vehicle mass mro, with a correction function accounting for transmission losses, virtual mass increase, tyre slip, and turbo delay, and to allow manufacturers to alternatively determine reference acceleration by discrete measurements.

Document presents considerations on factor x used in the Sound Expectation Model to split constant speed test results into tyre rolling sound and power train mechanic references. Factor x values are concentrated between 80 and 99, indicating tyre dominance. Small variations in measurements cause disproportional variability in the minor sound source when one source dominates. Two options are proposed: Option 1 requires factor x determined during type approval to be reported and used for subsequent assessments, with any redetermination not exceeding the type approval value; Option 2 requires the power train reference from type approval to be used for all further assessments regardless of measurement variations.

The Task Force Data Analysis meeting scheduled for 15 September 2026 will discuss database pilot documents covering amendments to factor x, reference acceleration, AVAS term considerations, simplified EV models, and RD-ASEP model slopes. The task force will prepare proposals based on draft UN R51.04 for items 13–19 from the Editing TF issues list and address a question regarding the phrase “but no more than 2.0 m/s” in paragraph 3.1.2.1.4.3 concerning acceleration values for vehicles with single gear ratios.

Proposal to establish revised terms of reference for IWG RD-ASEP covering vehicles of categories M₁, N₁, and L₃. For M₁ and N₁ vehicles, objectives include modifying current regulations to mandate revised RD-ASEP, updating Annex 9, deleting Annex 7, and developing coordination between UN R51 and UN R138. For L₃ vehicles, objectives include updating RD-ASEP limits. The IWG shall be chaired by Germany with OICA and IMMA as secretaries, shall report to GRBP, and shall present comprehensive proposals for M₁ and N₁ by February 2028.

Proposal for a Guideline regarding the Interpretation of Paragraph 6.2.3. ASEP in the 03 series of amendments to UN Regulation No. 51, updating Informal Document GRB-68-03 and based on GRB/2005/5 and GRB/2010/9. Part A addresses internal combustion and hybrid vehicles when the combustion engine is operating, defining typical on-road driving as vehicle speeds between 15 km/h and 100 km/h, accelerations not exceeding 2 m/s² and vehicle performance not exceeding 35 m/s², and engine speeds of at least 1.5 times idle speed and not exceeding the maximum outlined in Annex 7. Significant deviation means sound level exceeding reference values by at least 6 dB(A). Type approval test results derive from Annex 3 or Annex 7 values, with reference values established using regression curves or calculation principles. Part B addresses electric and hybrid vehicles propelled electrically only, extending guidance to electrified vehicles and Enhanced Exterior Sound introduced by Supplement 11. Typical on-road driving for electric vehicles includes vehicle speeds greater than 0 km/h and up to 100 km/h and standstill covered by UN-R 138. Significant deviation for electric vehicles is at least 3–6 dB(A).

The 15th RD-ASEP informal group session will be held at Nissan Technical Center Europe Spain in Barcelona. The venue is located 11 minutes walk from Mercabarna Metro Station Line 9S. Participants should make hotel reservations independently; options include areas near metro line L9S or city center near metro line L5, which connects with L9S. Participants must provide last name, first name, phone number, company name, and email in advance.

Rationale for Figure Part B.5 of GRBP-84-36-Rev.1

Proposal to amend para. 6.2.1.1. to permit testing of vehicle sound either indoors or outdoors with equivalent results, add new Annex 11 specifying indoor testing provisions, amend Annex 1 to insert para. 8.5. and 8.5.1. requiring documentation of test method selected, amend Annex 3 para. 1. to specify sound level meter requirements for indoor testing per IEC 651 and IEC 61672-3, amend Annex 3 para. 1.1.1. to provide calibration procedures for indoor testing per IEC 942:1988, amend Annex 3 para. 1.3. to exempt wind speed monitoring for indoor facilities, amend Annex 3 para. 2.1. and add para. 2.1.4. to specify outdoor and indoor test site requirements per ISO 362-3:2022 and ISO 26101, add para. 2.1.5. specifying indoor ambient conditions, add para. 2.2.7. addressing test mass for indoor dynamometer testing, amend Annex 3 para. 3. to specify outdoor and indoor test procedures per ISO 362-3:2022 Variant A, amend Annex 3 para. 3.1.1. to clarify outdoor testing microphone placement, add para. 3.1.1.4. defining virtual lines and simulated vehicle speeds for indoor testing, and renumber former paras. 3.1.1.4. and 3.1.1.5. as 3.1.1.5. and 3.1.1.6.