IWG RD-ASEP status report to GRBP-83 after the 10th session in December 2025. Work on RD-ASEP for UN R51 is developing a mandatory procedure after the monitoring phase, while R41 work has concluded. The Data Analysis Task Force reported on database sufficiency, boundary conditions, CVT vehicle modelling, and potential inclusion of N₂/N₃/M₂/M₃ vehicles. An Editing Task Force created a consolidated R51.04 draft reviewed in December. IWG RD-ASEP recommends no monitoring requirements be approved without corresponding mechanisms to collect, analyze, and report results. M category/R51 informal document submission expected September 2026 and working document February 2027. L-category/R41 requires no further action.

The subgroup on UN R51 and UN R138 met on 14 January 2026 to review comments on outcome documents. Switzerland’s sentence in 3.5. was retained for clarification. JASIC’s definition of EES footnote was changed to reference GRB-68-03. Transitional provisions remained unchanged with a new item added for Annex 1, Appendix 1. Agreement was reached on 6 dB allowance in Annex 7 paragraph 3.4. and 3 dB for three specific cases. A draft paragraph for GRB-68-03 justification will be submitted by email. Switzerland’s proposal SG-13-05-2025-07-30 will serve as basis. GRBP-82-39 includes examples for active systems generating EES and creation of part B for electric vehicles. Work on RD-

Proposal to amend GRBP/2026/4. Amendments to UN Regulation No. 51 include updates to the Table of Symbols in paragraph 2.24; new definitions for Active Sound Source, Enhanced Exterior Sound (EES), and Vehicle Master Control Switch; specifications for EES operation requiring driver intentional action and default deactivation; sound limits complying with UN-Regulation No. 138 below 20 km/h and this Regulation from 20 to 80 km/h; transitional provisions allowing extension of existing approvals for 24 months; modifications to Annex 7 control ranges, anchor points, and slope calculations for electrically propelled vehicles; and updates to Annex 1 and Annex 3 regarding EES systems. GRB-68-03 commitment to add EES guidance document is confirmed.

The secretary reported on C1 tyre testing activities. The Netherlands and Germany noted potential delays in Normal tyre testing at high temperature by end of March due to temperature conditions. The co-chair presented a status report for GRBP’s 83rd session, which the group approved. Future meetings are scheduled for February through April.

The GOIE on Tyre Noise Level Alignment in UN R117 targets reducing dispersion of measurements for tyres of Class C1 and C2 and investigating possibility to develop a test method with an SRTT as reference. An intermediate report will be presented to GRBP in September 2026, with a Working Document proposing evolution of the test method by September 2027. Five meetings have been held with 13 test centres from France, Japan, Netherlands, Spain and ETRTO. Eight of thirteen test centres have completed tests on 15 C1 and 5 C2 Japanese market tyres, with completion targeted for mid-2026.

Proposal to supersede document GRBP/2026/4 intended to introduce a “default mode”, to specify requirements to be applied to the emission of Enhanced Exterior Sound (EES), with corresponding transitional provisions, and to draw a limit curve to introduce electric vehicles and hybrid electric vehicles that can be propelled without an internal combustion engine operating in the scope of ASEP (Annex 7).