The IWG RD-ASEP informal group is developing a mandatory procedure for UN R51 after the monitoring phase. The Analysis Task Force determined vehicle databases and expectation model are suitable for RD-ASEP use. The Editing Task Force created a consolidated R51.04 draft incorporating R51.03 Supplements up to Supplement 11, with revised manipulation and defeat device provisions and mandatory random testing for approval. R51.04 RD-ASEP expands vehicle speed range to 0-100 km/hr, adds vehicle performance criteria, requires testing for approval, and permits random test points and any acceleration position, compared to R51.03 ASEP.

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’.

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.

This document provides guidance for interpreting paragraph 6.2.3 of UN R51.03 concerning Additional Sound Emission Provisions for vehicles of category M₁ and N₁. Part A clarifies that typical on-road driving means driving at speeds between 15–100 km/h with accelerations not exceeding 2 m/s² and vehicle performance not exceeding 35 m/s, across any gear except reverse at engine speeds of at least 1.5 times idle speed and not exceeding the maximum specified in Annex 7. Significant deviation is defined as a sound level exceeding the reference value by at least 6 dB(A). Type approval test results derive from Annex 3 or Annex 7, with reference values determined using regression curves for Slope-Assessment or calculation principles for Lurban-Assessment. Part B addresses electric and hybrid vehicles when electrically propelled, extending ASEP scope under Supplement 11, applying comparable principles with modifications regarding active sound enhancement systems and operating speed ranges between 20–100 km/h for electric vehicles.