UN R13 Supplement 8 (12 series) · UNECE Regulation No. 13 (ECE R13) — Uniform provisions concerning the approval of vehicles of categories M, N and O with regard to braking.
UN R13 — Supplement 8 to the 12 series of amendments
Supplement 7 → 8
- What changed
- New paragraph 5.2.2.26. sets requirements for the dynamo function of e-axle trailers, such as a 22 kW retardation power limit for O3 and O4 trailers.
- For the static parking brake requirements, a park lock device may now be used, alone or with means acting on the braking surfaces (para. 5.2.1.10.).
- Under new paragraph 2.2.7. of Annex 4, only one braking control must be used for each secondary braking test condition.
- Why
- The provisions for trailers with e-axles (dynamo function) aim to increase the efficiency of these vehicles.
- The proposal on the park lock device aimed at allowing for the type approval of park locks.
- OICA proposed to clarify that any braking system control may be used to test the effectiveness of the secondary braking system in failure conditions.
Q1What changed52 changes
E-axle trailers: scope and definitions (paras 1.2.6., 2.45. to 2.47.)
This Regulation does not cover e-axle trailers with e-axles providing electric propulsion and/or incorporating an electric regenerative braking system (new para. 1.2.6.). An “e-axle” is now defined as an axle mounted to a vehicle of category O generating electrical energy and/or providing electrical propulsion (para. 2.45.). An “e-axle trailer” is a trailer of category O with at least one e-axle, “while the trailer is not designed to move on its own” (para. 2.46.). The “Dynamo function” of an e-axle trailer is the capability of a trailer “to provide for the conversion of vehicle kinetic energy into electrical energy without affecting the forces developed by the braking system” (para. 2.47.). A dynamo function is not part of the braking system and not considered as a brake.
Requirements for the dynamo function of e-axle trailers (paras 5.2.2.26. to 5.2.2.26.5.)
Trailers of Category O1 and O2 with a dynamo function must not be approved under this Regulation until uniform technical provisions are agreed. For the complete trailer of Category O3 and/or O4, the dynamo function must not provide a retardation power of more than 22 kW. The owner’s manual must state that, in a multiple trailer combination of Category O3 and/or O4, the 22 kW limit applies to “the sum of the retardation power of all dynamo function devices of the combination”. If the dynamo function can generate a braking rate of more than 0.04 per wheel, it must be controlled so that it “does not cause wheel locking and has no critical impact on the vehicle behaviour”. Its operation must be assessed according to Annex 18, and O3 and O4 trailers must meet Annexes 13 and 21 with it enabled. For a dynamo function according to paragraph 5.2.2.26.2., paragraph 5.2.2.26.5. sets comparison tests with and without the dynamo function active.
Dynamo function and e-axles in brake tests (Annexes 4, 10 and 19)
In Annex 4, paragraph 1.4.1.2.2., the e-axle functions of an e-axle trailer must not be used during the brake applications. New paragraph 1.7.1.3. of Annex 4 says the dynamo function, if any, must not be used during the brake applications. Annex 10, paragraph 1.1.1., now also excludes the retarding force of a dynamo function when vehicle performance under that annex is determined. In Annex 19, paragraphs 4.5.1.5. and 4.5.1.6. now also require any dynamo function to be disengaged, like any endurance braking system.
E-axles in anti-lock rules and trailer documents (Annexes 2, 5, 19, 20 and 21)
Annex 5 (certain ADR vehicles) sets endurance braking rules for power-driven vehicles over 16 tonnes maximum mass or authorized to tow O4 trailers. For these vehicles, paragraph 2.2.1.2. also requires an e-axle function to switch off after an anti-lock electrical failure, with one exception. For these vehicles, paragraph 2.2.1.3. also requires anti-lock control of an e-axle so its axle cannot lock above 15 km/h, with the same exception. The exception: an e-axle with a dynamo function is excluded if the prevention of wheel locking is not based on the anti-lock braking system. Annex 2 adds item 14.18. on e-axles with a dynamo function, and Annexes 19 (Appendices 5 and 7) and 21 add e-axles to their lists. Annex 20, paragraph 3.2.1.3., now names e-axles among the axles whose number and arrangement must not differ from the reference trailer.
Park lock device in the parking braking system (paras 5.1.4.5.3., 5.2.1.10.)
For the static parking brake requirements of Annex 4, paragraphs 2.3.1 and 2.3.2, the parking braking system may now use a park lock device. The device may act as an alternative to or in combination with means acting on the braking surfaces (para. 5.2.1.10.). The park lock device must consist of components of an adequate strength and give equal effectiveness compared to layouts purely acting on the braking surfaces. After complete engagement of a parking braking system that contains a park lock device, the affected wheels must not move. The manufacturer must specify on which axle or axles the park lock device acts, “on the vehicle in a visible position in indelible form” or in another freely available way (para. 5.1.4.5.3.). The rule on disconnection of the parking braking system now also covers the park lock device and no longer includes the words “or by an ADS”.
Warning signals for the park lock device (paras 5.2.1.26.2.3., 5.2.1.26.6.)
New paragraph 5.2.1.26.6. covers a parking braking system that contains a park lock device and has detected at standstill a request to apply it. A red warning signal must then flash until the park lock device is completely engaged, “unless the parking braking system is preventing further movement of the braked wheels”. Where a separate red warning signal that meets all requirements of 5.2.1.29.3. normally indicates actuation of the park lock device, this signal must be used. In paragraph 5.2.1.26.2.3., the word “clamping” is replaced by “engagement” in the condition for suppressing the flashing red warning signal.
One braking control for each secondary braking test condition (Annex 4, para. 2.2.7.)
Under new paragraph 2.2.7. of Annex 4, only one braking control must be used for each secondary braking test condition of paragraph 2.2.5. Examples are the service braking control and the parking brake control. A different braking control may be used in the unladen and the fully laden condition, as described by the vehicle manufacturer in Annex 2.
Q2Why it changed
- Proposed by
- Experts from CLEPA and OICA (park lock device); experts from OICA (secondary braking test); experts from CLCCR, CLEPA and OICA (e-axle trailers)
- Working party
- GRVA, 23rd session (September 2025)
Reasons
The Chair of GRVA presented the draft supplement and recommended its submission to AC.1. It includes provisions for the approval of trailers with e-axles (dynamo function), which aim to increase the efficiency of these vehicles.
Source
“The Chair of GRVA presented the draft supplement to UN Regulation No. 13 (Heavy vehicle braking) including provisions for the approval of trailers with e-axles (dynamo function) aimed to increase the efficiency of these vehicles”
CLEPA recalled that their proposal aimed at allowing for the type approval of park locks. The proposal addressed the type approval of a park lock device as an alternative to, or in combination with, the friction parking brake. ECE/TRANS/WP.29/GRVA/2025/13, on which the proposal is based, aimed to let a park lock device fulfil the static requirements for parking braking systems. That document said that the word “engagement” seems more appropriate than “clamping”, because the vehicle is kept in a static position.
Sources (4)
“The representative of CLEPA recalled the purpose of their proposal for amendments to UN Regulation No. 13 (ECE/TRANS/WP.29/GRVA/2025/34) aimed at allowing for the type-approval of park-locks”
“addressing the type-approval of a park lock device as an alternative to or in combination with the friction parking braking to hold the vehicle. It is based on ECE/TRANS/WP.29/GRVA/2025/13 amended by GRVA-20-06/Rev.1”
“This amendment aims to enable the use of a park lock device as an alternative to a friction type parking braking system to fulfil the static requirements of UN Regulation No. 13 for parking braking systems.”
“As the combination of friction type and park lock device or a combination of both will keep the vehicle in a static position, the word “engagement” seems more appropriate than “clamping””
OICA proposed to clarify that any braking system control may be used to test the effectiveness of the secondary braking system in failure conditions. Different interpretations existed, and some Technical Services asked for the same braking system control in both laden and unladen test conditions. According to OICA, the content and the performance requirements do not change. Only the test duration and the effort to check complex vehicle designs are optimized.
Sources (3)
“The proposal aims to clarify that the use of any braking system control for testing the effectiveness of the secondary braking system in failure conditions is allowed.”
“The issue is that different interpretation exists, leading some Technical Services to request the usage of the same braking system control in both laden and unladen test conditions.”
“Neither the content nor the performance requirements are changing, but only the test duration and the efforts needed to check complex vehicle designs”
Proposer's reason (informal document GRVA-23-11-Rev.2)
Until a further amendment is agreed, trailers with electric propulsion and electric regenerative braking systems are to stay outside the scope of this Regulation. The power of the dynamo function is limited to protect motor vehicle functions of heavy vehicles, such as mass estimation, from relevant impact. A target electric power of 20 kW covers most use cases, for example the supply of cooling systems for O3 and O4 trailers. Paragraph 5.2.2.26.2. aims to avoid locking of wheels that the dynamo function affects. Below a braking rate of 0.04, like the friction value of wet ice, wheels will not lock. During tests, retardation forces of the dynamo function are not to support the performance of the braking functions.
Submitted by the experts from CLCCR, CLEPA and OICA. Working party adoption: ECE/TRANS/WP.29/GRVA/23, para. 63.
Sources (5)
“Until further amendment of Reg 13 is developed and agreed, trailers with electric propulsion and electric regenerative braking systems shall not be in the scope of Reg 13 approvals.”
“power of the dynamo function shall be limited to protect motor vehicle functions of heavy vehicles like mass estimation from relevant impact by the trailer dynamo function”
“An electric power of 20 kW is a target value which covers most use cases of a dynamo function e.g. supply of cooling systems for O3 and O4 trailers.”
“purpose of this requirement is to avoid locking of wheel(s) that are impacted by the dynamo function. If the wheels braking rate is below 0.04 (like the friction value of wet ice), wheels will not lock.”
“During testing the performance of the braking functions shall not be supported by retardation forces of the dynamo function.”
Document trail
- 2024-11ProposalECE/TRANS/WP.29/GRVA/2025/13Proposal by experts from OICA and CLEPA on the park lock device
- 2025-04ProposalECE/TRANS/WP.29/GRVA/2025/34Proposal by experts from CLEPA and OICA on park lock device approval
- 2025-09RevisedECE/TRANS/WP.29/GRVA/2025/46/Rev.1Revised proposal by experts from OICA on the secondary braking test
- —Amended in sessionGRVA-23-07-Rev.2Changes by CLEPA and OICA to the park lock proposal
- —RevisedGRVA-23-11-Rev.2Proposal by experts from CLCCR, CLEPA and OICA on e-axle trailers, replacing ECE/TRANS/WP.29/GRVA/2025/15
- —Working party adoptsECE/TRANS/WP.29/GRVA/23GRVA session report, paras. 59, 61 and 63
- 2025-12Sent to WP.29ECE/TRANS/WP.29/2026/13Text that GRVA sent to WP.29 and AC.1
- 2026-03WP.29 adoptsECE/TRANS/WP.29/1190Adopted at the 198th session (session report, para. 114)
- 2026-09-30In forceC.N.401.2026.TREATIES-XI.B.16.13UN depositary notification
Q3Who is affected
Vehicle manufacturer
- Keep the retardation power of the dynamo function at or below 22 kW for the complete O3 or O4 trailer.
- Add the 22 kW statement for multiple trailer combinations of Category O3 and/or O4 to the owner’s manual.
- If the dynamo function can generate a braking rate above 0.04 per wheel, control it so that it “does not cause wheel locking and has no critical impact on the vehicle behaviour”.
- Prepare evidence that O3 and O4 trailers comply with Annexes 13 and 21 with the dynamo function enabled.
- Specify on which axle or axles the park lock device acts (para. 5.1.4.5.3.).
- For parking braking systems with a park lock device, check that the affected wheels do not move after complete engagement.
- Check how disconnection of the parking braking system is controlled, because the rule no longer includes “or by an ADS”.
Component supplier
- Give the vehicle manufacturer the data for the Annex 18 assessment of the dynamo function (para. 5.2.2.26.3.).
- Make sure that your park lock devices consist of components of an adequate strength.
Technical service / Approval authority
- Check the maximum power of the dynamo function at type approval with one of the four methods of paragraph 5.2.2.26.1.
- For a dynamo function under paragraph 5.2.2.26.2., check the comparison tests with and without it active (para. 5.2.2.26.5.).
- If surface friction is too high or braking rate too low to lock the wheels, agree with the manufacturer “a way to increase the retardation power or reduce the vertical axle load of the e-axle”.
- On e-axle trailers, check that the e-axle functions and any dynamo function are not used in Annex 4 brake applications.
- In secondary braking tests, check that only one braking control is used for each test condition (Annex 4, para. 2.2.7.).
- Accept a different braking control for the unladen and fully laden conditions if the manufacturer describes it in Annex 2.
- Check the red warning signal of parking braking systems with a park lock device against paragraph 5.2.1.26.6.
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ⓘ This report gives advice only. It is not legal or type-approval advice.
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