UN R138 — 02 series of amendments

New paragraph 2.2. defines “natural sound” as “sound coming from the vehicle and its components as a result of e.g. providing propulsion, braking, steering, cooling, or any other function”. An exterior sound enhancement system, as defined in UN Regulation No. 51, Annex 9, paragraph 2.2., does not produce natural sound. New paragraph 2.3.1. defines “AVAS sound” as a synthetic created sound that an AVAS can control. The AVAS sound “provides only acoustic safety information to pedestrians and other road users on the vehicle's presence and operation”. New paragraph 2.11. defines the “mandatory speed range” as the speed range where an AVAS must emit sound (AVAS sound) to fulfil the requirements of this Regulation. New paragraph 2.12. defines the “lowest frequency of interest” as “the frequency below which there is no signal content relevant to the measurement of sound emission for the vehicle under test”.

The specifications now apply “in forward and reverse driving condition” for the mandatory speed range of greater than 0 km/h up to and inclusive 20 km/h. An AVAS sound is only allowed in forward driving direction in the speed range mentioned in Table 2a and for all speeds in reverse direction. Outside the mandatory speed range, an AVAS may operate, and the maximum levels of Tables 2a and 2b apply to the AVAS sound. If a vehicle without an AVAS fulfils “the minimum overall levels as specified in Table 2a below with a margin of +3 dB(A) by its natural sound”, the Table 3 one-third octave band specification and the paragraph 6.2.3. frequency shift do not apply. In the mandatory speed range, the AVAS sound must always be emitted, and any pause function is allowed only outside that range. Before this series, the text said “Any pause function as defined in paragraph 2.7. shall be prohibited”.

Paragraph 6.2.4. is now titled “Sound of the vehicle in standstill condition” instead of “Stationary sound”. In standstill condition with the propulsion system activated, an AVAS sound is allowed only if the gear selector is not in Park (automatic transmission). For a vehicle with a manual transmission, the condition is instead that the parking brake is released. When the vehicle is in standstill condition and the gear selector is in reverse driving position, an AVAS sound is mandatory. An AVAS sound in standstill condition must comply with paragraph 6.2.8., Tables 2a and 2b. For a vehicle in scope of UN Regulation No. 165, an audible reverse warning signal above the Table 2b minimum overall levels “is deemed to fulfil this regulation in reverse driving, without the sound from an AVAS”.

Paragraph 6.2.8. is now titled “Specifications on minimum and maximum sound level for AVAS sound”, and paragraph 6.2.9. on minimum sound levels is deleted. Table 2a gives AVAS minimum and maximum overall sound pressure levels for forward driving, and Table 2b gives them for reverse driving. Paragraph 6.2.1.1.2. now refers to Table 3 of paragraph 6.2.8. for the one-third octave bands, instead of Table 2. In the speed range of Tables 2a and 2b and under Annex 3, paragraph 3.3.2., a vehicle with an AVAS “shall not emit an AVAS overall sound level of more than 75 dB(A), if driving in forward direction”. During measurement in reverse, the maximum level requirement in the frontline of the vehicle for forward driving must also be fulfilled. A manufacturer declaration can state both the 75 dB(A) test and this reverse requirement.

Besides the approval test speeds of 10 km/h and 20 km/h, “Compliance with other speeds covered by Table 2a of paragraph 6.2.8. shall be given by a manufacturer declaration (Annex 4)”. Paragraph 6.2.2.1. now takes the minimum overall sound pressure level from Table 2b of paragraph 6.2.8., instead of Table 2, column 5. Compliance with other speeds covered by Table 2b must be given by a manufacturer declaration (Annex 4). The manufacturer declaration (Annex 4) must confirm “compliance with paragraph 6.2.8., Tables 2a and 2b of non-tested sound modes during type approval in respect to Annex 3, paragraph 3.2.3”. All combinations of AVAS sound level variations and AVAS sound must fulfil paragraph 6.2.8., Table 2a, Table 2b and Table 3. In new Annex 4, the manufacturer attests that vehicles of the type “comply with the requirements of paragraph 6. of UN Regulation No. 138 in all vehicle modes and all selectable driving sounds”.

Paragraph 2.3.2. on the vehicle A-weighted sound pressure level now sets “background noise requirements” instead of “measurement correction criteria”. The overall A-weighted background noise level must be at least 6 dB below the measurement of the vehicle or AVAS under test. The former rules for correcting test results for background noise are deleted. In case of a 5 microphone array, the microphones “shall be located 1,6 m ± 0,02 m, 1,4 m ± 0,02 m, 1,2 m ± 0,02 m, 1,0 m ± 0,02 m, 0,8 m ± 0,02 m above the ground level”. Method (E), the “Test of the AVAS without a vehicle in an indoor facility”, is deleted. Measurements are made at mass in running order with an allowable tolerance of +/- 25 %, instead of 15 %.

In Conformity of Production tests, only the tests of paragraph 6.2. are performed. The vehicle type conforms if the sound level of a vehicle tested under Annex 3, paragraphs 3.3.2. and 3.3.3., “does not exceed by more than 1 dB(A) the maximum sound pressure level limit value and without a tolerance to the minimum sound pressure level limit value” of Tables 2a and 2b. If Conformity of Production uses Method (A) and the original type approval used Methods (B) or (D), “an additional 1 dB(A) tolerance is applied only for maximum overall sound pressure level requirements”. Until 24 September 2028, ISO 10844:2014 may be applied as an alternative to ISO 10844:2021 to check the test track (Annex 3, paragraph 2.1.2.). From 1 September 2026, Contracting Parties applying this Regulation need not accept 01 series type approvals first issued after 1 September 2026. From 1 September 2028, Contracting Parties applying this Regulation need not accept type approvals to the 01 series of amendments.