UN R157 Supplement 4 (01 series) · UNECE Regulation No. 157 (ECE R157) — Uniform provisions concerning the approval of vehicles with regard to Automated Lane Keeping Systems.
UN R157 — Supplement 4 to the 01 series of amendments
Supplement 3 → 4
- What changed
- For Categories N3 or M3, a regular lane change may start only if the target lane's permitted maximum speed is limited for all vehicle categories.
- The footnote that permitted initiation of a regular lane change only for a vehicle of Category M1 or N1 is deleted.
- Paragraphs 5.5.5. and 6.2.2. now use “initiation of the powertrain” instead of “engine start/run cycle”.
- Why
- Lane changes of vehicles of Categories N3 or M3 into lanes without a speed restriction can be a serious safety threat to approaching vehicles.
- The proposal of Germany aimed to address the content of the footnote in paragraph 5.2.6.5.1. and to allow lane changes for more vehicle categories.
- The words “engine” and “run cycle” imply a type of technology and may keep some ambiguity.
Q1What changed8 changes
Regular lane changes: new condition (d) and deleted footnote (para. 5.2.6.5.1.)
The activated system must only initiate a regular lane change if the listed conditions are fulfilled. For Categories N3 or M3, new condition (d) requires that the target lane's permitted maximum speed is limited for all vehicle categories. The footnote that permitted initiation of a regular lane change only for a vehicle of Category M1 or N1 is deleted. The deleted footnote also said that GRVA must review its presence before 1 September 2024.
Reactivation after a minimum risk manoeuvre (para. 5.5.5.)
After the end of any minimum risk manoeuvre, reactivation of the system is possible only after a new initiation of the powertrain. Before, reactivation was possible only after each new engine start/run cycle. Paragraph 6.2.2. excludes automatic engine starts, for example by a stop/start system, from the term “initiation of the powertrain” in the whole Regulation.
Off mode at the initiation of the powertrain (para. 6.2.2.)
The default status of the system must be off mode at the initiation of the powertrain. Before, the off mode applied at the initiation of each new engine start/run cycle. An automatic engine start (or run cycle), for example by a stop/start system, is not an “initiation of the powertrain” anywhere in the Regulation. The Regulation no longer has the old sentence that said “this requirement” does not apply to automatic starts. In Annex 5, the test/check entry for paragraph 6.2.2. uses the words “Off mode after new engine start/run”.
New footnote that refers to the M.R.2 propulsion system definitions
A new footnote refers to the vehicle propulsion system definitions in Mutual Resolution No. 2 (M.R.2), document ECE/TRANS/WP.29/1121.
- The system must be in its default off mode at the initiation of the powertrain (6.2.2.).
- A new initiation of the powertrain meets the condition for reactivation after a minimum risk manoeuvre (5.5.5.).
- The off-mode default of paragraph 6.2.2. does not apply to an automatic engine start, for example by a stop/start system.
- An automatic engine start, for example by a stop/start system, does not meet the 5.5.5. condition for reactivation after a minimum risk manoeuvre.
The earlier text of paragraphs 5.5.5. and 6.2.2. used “each new engine start/run cycle”.
Based on: paragraphs 5.5.5. and 6.2.2. of UN Regulation No. 157 as amended by Supplement 4 to the 01 series of amendments (ECE/TRANS/WP.29/2025/64)
Q2Why it changed
- Proposed by
- Expert from Germany; expert from the United Kingdom of Great Britain and Northern Ireland
- Working party
- GRVA, 21st session (January 2025)
Reasons
It is proposed to allow regular lane changes of heavy vehicles only into target lanes where a speed limit applies. This takes into account the intended scope of the Regulation.
Source
“It is proposed that, with regard to the intended scope of the regulation and notwithstanding the current footnote in paragraph 5.2.6.5.1., regular lane changes of heavy vehicles shall only be allowed into target lanes where a speed limit applies.”
Lane changes of vehicles of Categories N3 or M3 into lanes without a speed restriction can be a serious safety threat to approaching vehicles. This threat is due to high speed differences. Because of this threat, relying on assumed speeds of approaching vehicles on the target lane, as per paragraph 5.2.6.7.2.1 (b), is not justifiable.
Sources (2)
“Lane changes of heavy vehicles of Categories N3 or M3 into not speed restricted lanes can establish a serious safety threat to approaching vehicles due to high speed differences.”
“relying on assumption of their speed – as per paragraph 5.2.6.7.2.1 (b) – is not justifiable.”
The proposal of Germany aimed to address the content of the footnote in paragraph 5.2.6.5.1. and to allow lane changes for more vehicle categories.
Source
“aimed at addressing the content of the footnote in paragraph 5.2.6.5.1 (ECE/TRANS/WP.29/GRVA/2025/2) and allowing lane changes for more vehicle categories.”
The words “engine” and “run cycle” imply a type of technology and may keep some ambiguity. The generic terms of Mutual Resolution No. 2 (M.R.2) do not depend on fuel type or technology. M.R.2 therefore gives a basis for provisions that can be technology neutral.
Sources (3)
“Continuing to refer to ‘engine’ or ‘run cycle’ is still implying a technology type and therefore may retain a level of ambiguity.”
“was specifically created to establish uniform definitions for vehicle propulsion systems and created generic terms for components and aspects of propulsion systems that are independent of fuel type or technology used”
“It therefore gives the basis for establishing provisions that can be technology neutral.”
The M.R.2 definition of “powertrain” gives a generic term. The term covers the aspect of the vehicle that the text must refer to for the default state of systems after initialisation. The term “powertrain” also makes the provisions simpler.
Sources (2)
“Using the definition of ‘powertrain’ from M.R.2 provides a generic term that sufficiently covers the aspect of a vehicle which needs to be referred to when considering the default state of systems following initialisation.”
“Also using the term ‘powertrain’ simplifies the respective provisions.”
Document trail
- 2024-07ProposalECE/TRANS/WP.29/GRVA/2024/30Earlier proposal by the expert from the United Kingdom
- —ProposalGRVA-20-04Earlier proposal by the expert from Germany
- —RevisedGRVA-20-42Changes from the discussions at the 20th GRVA session
- 2024-11ProposalECE/TRANS/WP.29/GRVA/2025/2Proposal by the expert from Germany to review footnote 3
- 2024-11RevisedECE/TRANS/WP.29/GRVA/2025/4Revised proposal by the expert from the United Kingdom
- —Amended in sessionGRVA-21-07Amendments to ECE/TRANS/WP.29/GRVA/2025/2 by the expert from Japan
- —Working party adoptsECE/TRANS/WP.29/GRVA/21Adoption by GRVA at its 21st session (para. 26)
- 2025-04Sent to WP.29ECE/TRANS/WP.29/2025/64Text submitted to WP.29 and AC.1
- 2025-06WP.29 adoptsECE/TRANS/WP.29/1186Adopted at the 196th session (session report, para. 111)
- 2026-01-11In forceC.N.46.2026.TREATIES-XI.B.16.157UN depositary notification
Q3Who is affected
Vehicle manufacturer
- Make sure N3 or M3 vehicles initiate regular lane changes only into lanes with speed limits for all vehicle categories.
- Make sure that the default status of the system is off mode at the initiation of the powertrain (6.2.2.).
- Make sure that reactivation after a minimum risk manoeuvre is possible only after a new initiation of the powertrain (5.5.5.).
- Test that an automatic engine start by a stop/start system does not count as an initiation of the powertrain.
Component supplier
- Make sure that your software logic for paragraphs 5.5.5. and 6.2.2. uses the new term “initiation of the powertrain”.
- Make sure that your software does not treat an automatic stop/start engine start as an initiation of the powertrain.
Technical service / Approval authority
- Check that N3 or M3 vehicles initiate regular lane changes only into lanes with speed limits for all vehicle categories.
- When you assess paragraph 5.5.5., do not accept an automatic stop/start engine start as an initiation of the powertrain.
- Compare the Annex 5 test/check entry “Off mode after new engine start/run” with the new paragraph 6.2.2.
- For the term “powertrain”, use the definitions in M.R.2 (document ECE/TRANS/WP.29/1121).
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ⓘ This report gives advice only. It is not legal or type-approval advice.