UN R13 Supplement 3 (14 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 3 to the 14 series of amendments
Supplement 2 → 3
- What changed
- This supplement adds definitions for e-axles, e-axle trailers and the dynamo function, and special requirements for the dynamo function of e-axle trailers.
- Brake demand values of electrical transmission braking systems must also be readable through an electronic vehicle interface, unless no suitable interface exists.
- A park lock device may now meet the static parking brake requirements, and Annex 4 adds a rule on braking controls for secondary braking tests.
- Why
- The provisions for trailers with e-axles (dynamo function) aimed to increase the efficiency of these vehicles.
- The brake demand value proposal aimed to allow the live reading of brake demand values during Periodic Technical Inspections (PTI).
- The park lock proposal aimed to allow type-approval of park locks; another proposal aimed to clarify the use of braking controls in secondary braking tests.
Q1What changed55 changes
E-axle trailers: scope and new definitions (paras. 1.2.6. and 2.57. to 2.59.)
This Regulation now does not cover e-axle trailers with e-axles that provide electric propulsion and/or include an electric regenerative braking system (para. 1.2.6.). New paragraph 2.57. defines an “e-axle” as an axle on a vehicle of category O that generates electrical energy and/or provides electrical propulsion. Paragraph 2.58. defines an “e-axle trailer”: a trailer of category O with at least one e-axle, not designed to move on its own. Paragraph 2.59. defines the “dynamo function” of an e-axle trailer. It is the capability of a trailer to convert vehicle kinetic energy into electrical energy without affecting the forces developed by the braking system. A dynamo function is not part of the braking system and is not considered as a brake.
Dynamo function of e-axle trailers: limits and tests (para. 5.2.2.26.)
Trailers of Category O1 and O2 with a dynamo function must not be approved under this Regulation until uniform technical provisions have been agreed. For a complete trailer of Category O3 and/or O4, the dynamo function must not give more than 22 kW of retardation power. If the dynamo function can generate a braking rate above 0.04 per wheel, it must not cause wheel locking or critical impact on vehicle behaviour. The operation of the dynamo function must be assessed according to Annex 18. For trailers of Categories O3 or O4, compliance with Annexes 13 and 21 must be shown with the dynamo function enabled. For a dynamo function under paragraph 5.2.2.26.2., tests with and without the dynamo function active must show that the wheels are prevented from locking.
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.
Brake demand values through an electronic vehicle interface (paras. 2.60., 5.1.4.6.2.1. and 12.1.7.)
For an electrical transmission braking system, the brake demand value(s) must still be displayed on the vehicle during the roller brake test. Except where no suitable interface exists, it must now also be possible to read them through an electronic vehicle interface (for example the OBD port). The vehicle manufacturer must now also describe how to access those values, not only how to display them. New paragraph 2.60. says an “electronic vehicle interface” provides access to real time parameters of the braking system specified within this regulation. For 24 months after this supplement enters into force, Contracting Parties can continue to grant or extend 14 series approvals without the paragraph 5.1.4.6.2.1. amendments.
Park lock device (paras. 5.1.4.5.4., 5.2.1.10. and 5.2.1.26.6.)
Under paragraph 5.2.1.10., a park lock device may meet the static parking brake requirements, instead of or with means acting on the braking surfaces. The device must give equal effectiveness, and the affected wheels must not move after complete engagement of the parking braking system. If a park lock device is fitted, the manufacturer must specify on which axle or axles it acts (paragraph 5.1.4.5.4.). New paragraph 5.2.1.26.6. adds special requirements for a park lock device. Unless the parking brake holds the wheels, a red warning signal must flash after a standstill request until the park lock device is completely engaged. The rule on disconnection of the parking braking system now also covers the park lock device, and it no longer names an ADS.
Braking control in secondary braking tests (Annex 4, para. 2.2.7.)
New paragraph 2.2.7. of Annex 4 says only one braking control must be used for each secondary braking effectiveness test condition under 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 CLCCR, CLEPA and OICA (e-axle trailers); experts from CITA, with changes by experts from CITA, OICA and CLEPA (brake demand values); experts of CLEPA and OICA (park lock device); experts from OICA (secondary braking tests)
- Working party
- GRVA, 23rd session (September 2025)
Reasons
The Chair of GRVA presented the draft supplement to UN Regulation No. 13 (Heavy vehicle braking). The draft included provisions for the approval of trailers with e-axles (dynamo function), aimed to increase the efficiency of these vehicles.
Source
“including provisions for the approval of trailers with e-axles (dynamo function) aimed to increase the efficiency of these vehicles”
The brake demand value proposal aimed to allow the live reading of brake demand values during Periodic Technical Inspections (PTI). Its authors said that this is important for road safety, because it gives more accurate assessments of brake system performance. GRVA supported, as a condition for adoption, that all new vehicle approvals and extensions of existing approvals would need to comply after 24 months.
Sources (2)
“aimed to enabling the live reading of brake demand values during Periodic Technical Inspections (PTI), which is crucial for enhancing road safety by ensuring more accurate assessments of brake system performance”
“GRVA noted and supported as a condition for adoption the paragraph in the justification section stipulating that all new vehicle approvals and extensions to existing type approval would need to comply the requirements after 24 months.”
The representative of CLEPA said that the park lock proposal aimed to allow the type-approval of park locks. An earlier proposal aimed to let a park lock device, instead of a friction parking brake, meet the static parking brake requirements. That earlier proposal also said that “engagement” seems more appropriate than “clamping”, because these solutions keep the vehicle in a static position.
Sources (3)
“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”
“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””
The secondary braking proposal aimed to make clear that any braking system control may be used to test the secondary braking system in failure conditions. Interpretations differed, and some Technical Services asked for the same braking control in both laden and unladen tests. Its authors said that the performance requirements do not change; only the test duration and effort for 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 (e.g. heavy 6x4 tractor with 4 x 30” parking brake chambers) are optimized.”
Proposer's reason (informal document GRVA-23-11-Rev.2)
The proposers said that trailers with electric propulsion and electric regenerative braking systems stay out of scope until a further amendment is agreed. The dynamo power limit aims to protect motor vehicle functions of heavy vehicles, such as mass estimation, from the trailer dynamo function. The wheel-locking requirement aims to avoid locking of wheels affected by the dynamo function; below a braking rate of 0.04, wheels will not lock.
Submitted by Experts from CLCCR, CLEPA and OICA. Working party adoption: ECE/TRANS/WP.29/GRVA/23, para. 63.
Sources (3)
“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”
“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.”
Document trail
- 2025-04ProposalECE/TRANS/WP.29/GRVA/2025/34Park lock device proposal by experts of CLEPA and OICA
- 2025-07ProposalECE/TRANS/WP.29/GRVA/2025/43Brake demand value proposal by experts from CITA
- 2025-09ProposalECE/TRANS/WP.29/GRVA/2025/46/Rev.1Revised secondary braking test proposal by experts from OICA
- —Amended in sessionGRVA-23-07-Rev.2Revised park lock device proposal at the 23rd GRVA session
- —Amended in sessionGRVA-23-18-Rev.1Changes to the brake demand value proposal by experts from CITA, OICA and CLEPA
- —ProposalGRVA-23-11-Rev.2E-axle trailer proposal by experts from CLCCR, CLEPA and OICA
- —Working party adoptsECE/TRANS/WP.29/GRVA/23GRVA session report, paras. 57, 59, 61 and 63
- 2025-12Sent to WP.29ECE/TRANS/WP.29/2026/11Text 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.399.2026.TREATIES-XI.B.16.13UN depositary notification
Q3Who is affected
Vehicle manufacturer
- Check whether your e-axle trailers fall under new item 1.2.6. of the vehicles this Regulation does not cover.
- Be ready to show compliance with the 22 kW dynamo limit for O3 and/or O4 trailers (paragraph 5.2.2.26.1.).
- Make sure the owner’s manual states the 22 kW sum rule for multiple trailer combinations of Category O3 and/or O4.
- If your dynamo function can exceed a braking rate of 0.04 per wheel, be ready for the paragraph 5.2.2.26.5. comparison.
- For Category O3 or O4 trailers, be ready to show Annex 13 and 21 compliance with the dynamo function enabled.
- For electrical transmission braking systems, describe how to display and access brake demand values (paragraph 5.1.4.6.2.1.).
- If you fit a park lock device, specify on which axle or axles it acts (paragraph 5.1.4.5.4.).
Component supplier
- Make sure your dynamo function control prevents wheel locking when it can exceed a braking rate of 0.04 per wheel.
- In the Annex 18 assessment, be ready to show how the dynamo function limits brake rate or prevents wheel locking.
- On electrical transmission braking systems, make brake demand values readable through an electronic vehicle interface, unless none is suitable.
- If you supply park lock devices, make sure they match the effectiveness of layouts acting only on braking surfaces.
Technical service / Approval authority
- For O3 and/or O4 trailers, check the dynamo function’s maximum power with one of the paragraph 5.2.2.26.1. methods.
- If wheels cannot lock in paragraph 5.2.2.26.5. tests, agree with the manufacturer on more retardation power or less axle load.
- On e-axle trailers, check that the e-axle functions are not used during the brake applications of Annex 4 tests.
- Use only one braking control for each secondary braking test condition (Annex 4, paragraph 2.2.7.).
- In secondary braking tests, accept a different braking control per load condition if the manufacturer describes it in Annex 2.
- Check the park lock device warning against the conditions of 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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