The agenda includes discussion of Terms of Reference from GRBP-78-13, procedural update from GRB-68-03, Analysis Task Force Report, Editing Task Force Report, R51.04 Issues List Review, draft R51.04 text review, Inside and Outside Boundary Condition discussions, and confirmation of next meeting date and place as August 31–September 1 in Geneva, Switzerland.

Current RD-ASEP derives the regulatory level based on the certified value without accounting for margin against regulatory values of the certified value. RD-ASEP additionally regulates partial acceleration, unlike current ASEP which only stipulates full-throttle acceleration. It is proposed that RD-ASEP should take into account a margin against the regulatory values of the certification values, similar to current ASEP, to prevent quiet vehicles such as BEVs from being unfairly deemed NG.

In vehicles with automatic transmissions, upshifts during testing cause SEM expected values to be exceeded. The proposal addresses three cases: vehicles with non-locked gear ratios, vehicles with locked gear ratios, and vehicles with only one gear ratio. For Case 1, such data does not meet conditions in R51-03 Annex 9 “4.5.2. Non-locked transmissions” and require no SEM correction. For Case 2, the proposal adds text to Annex 9 (7), Appendix 1, paragraphs 3.4. and 3.5., permitting substitution of maximum engine speed nMAX(AA-BB)TEST for nBBTEST when the maximum engine speed between AA’ and BB’ exceeds the engine speed at BB’.

Task Force Data Analysis (Sub Group to IWG RD-ASEP) held its 13th meeting on Wednesday, 3rd June 2026. The group reviewed database analysis including statistical analysis of differences between expected and measured sound levels, sub-model construction, and optimization calculations for parameter tables. Discussion addressed model construction concerns, vehicle failure differentiation, and data collection requirements including approval values according to UN R117. Next meetings are scheduled for Tuesday, 7th July and Monday, 24th August 2026.

This presentation analyzes RD-ASEP model performance using test run data from Annex_9_test_runs where both left and right sound were measured. Current model shows 1.3% of measurements above L_exp; without the 2 dB margin this increases to 8.4%. Model overestimates at low speeds and underestimates at higher accelerations. Tyre rolling sound parameters have most influence on results and dominate most of the data set. Optimizing all 13 parameters reduces mean absolute error from 2.1 to 1.1 dB. More high acceleration measurements are needed to reliably calibrate the dynamic component.