UN R173 Base text (01 series) · UNECE Regulation No. 173 (ECE R173) — Uniform provisions concerning the approval of the Installation of safety-belts, restraint systems, child restraint systems, ISOFIX child restraint systems and i-Size child restraint systems.
UN R173 — 01 series of amendments
Changes from 00 series of amendments
- What changed
- New paragraphs 5.2.3. to 5.2.3.2. add a strap length requirement for rear seating positions of M1 category vehicles, with conditions where it does not apply.
- New Annex 7 gives the tensile test method of the buckle strap assembly.
- From 1 September 2027, Contracting Parties applying this Regulation are not obliged to accept preceding-series approvals first issued after that date.
- Why
- The expert from Japan proposed the amendments to limit the slack of the buckle belt.
- According to the proposal, occupants can be thrown forward significantly in a frontal impact accident when the strap’s path to the buckle is not straight.
Q1What changed31 changes
Strap length in rear seating positions of M1 category vehicles (paras. 5.2.3. and 5.2.3.1.)
Under new paragraph 5.2.3., the requirement on the strap between the buckle point and the effective belt anchorage applies only to M1 rear seating positions. New paragraph 5.2.3.1.: the difference between actual strap length and the straight-line distance between point EA and Bd point must be 80 mm or less. This may be shown by the actual vehicle, parts, drawings, or 3D data, at the manufacturer's discretion. The manufacturer must demonstrate the correlation between the actual vehicle and/or parts and the drawing or 3D data.
Conditions where paragraph 5.2.3.1. does not apply (para. 5.2.3.2.)
Under new paragraph 5.2.3.2., the requirement of paragraph 5.2.3.1. does not apply if any of the following conditions are satisfied. (a) The safety-belt assembly is equipped with a pre-loading device. (b) With experimental data, simulation, or desktop strength calculations, the manufacturer demonstrates to the satisfaction of the Technical Service the same performance as point (c). (c) In the Annex 7 test, the buckle point movement is no greater than 80 mm at a tensile load of 1,000 N ± 50 N.
New definitions: EA, buckle point, Bd point and strap length (paras. 2.44. to 2.47.)
New paragraphs 2.44. to 2.47. define “Effective belt anchorage (EA)”, “Buckle point”, “Bd point” and “Strap length”. The “Buckle point” is the centre point of the connecting part between the buckle and the buckle strap. The “Bd point” is the position of the buckle point when the occupant is restrained in the design seat belt route. This occupant is a Hybrid III fiftieth percentile male dummy or Hybrid III fifth percentile female dummy, at the manufacturer's discretion. “Strap length” means the length along the centre line of the surface of buckle strap.
New Annex 7: Tensile test method of the buckle strap assembly
New Annex 7 gives the test procedure for the tensile test of the buckle strap assembly described in paragraph 5.2.3.2. The bracket that was attached to the vehicle anchorage is fixed to the lower part of the tensile testing machine. The buckle is fixed on the loading line so that the buckle point to EA point distance equals the straight-line EA to Bd point distance. The tension on the belt of the tongue is 4 ± 3 N. Then the buckle is released, and the test measures the load and the movement of the buckle.
Transitional provisions (paras. 11. to 11.2.3.)
New paragraph 11. gives transitional provisions. Contracting Parties applying this Regulation may grant type approvals according to any of the preceding series of amendments. They must continue to grant extensions of existing approvals to any of the preceding series of amendments. From the official entry into force of the 01 series, no Contracting Party applying this Regulation may refuse to grant or accept 01 series approvals. As from 1 September 2027, they are not obliged to accept approvals to any of the preceding series, first issued after 1 September 2027. They must continue to accept approvals issued according to the original form of this Regulation, first issued before 1 September 2027.
Example of the approval mark (Annex 2)
In Annex 2, the example approval mark and the text under it now show approval No. 011234 instead of 001234. The first two digits (01) indicate approval in accordance with UN Regulation No. 173 as amended by the 01 series of amendments. Before, the digits were (00) and the text said “in its original form”.
Reference to Table 1 of Appendix 3 (Annex 6, Appendix 2, para. 3.4.)
Under paragraph 3.4., removable interior fittings may be removed if the above requirements are not fulfilled when they were present. The requirements of paragraph 3. must then be verified again and fulfilled. In such a case, the corresponding information must now be included in Table 1 of Appendix 3 of this annex. Before, the paragraph referred to Table 2 and/or 3 of Appendix 3.
Q2Why it changed
- Proposed by
- Expert from Japan
- Working party
- GRSP, 76th session (December 2024)
Reasons
The strap’s paths between the effective safety-belt anchorage and the buckle are normally straight, like the test bench specified in UN Regulation No. 129. However, in some vehicles in the market, these paths are not straight and are curved along the cushion.
Sources (2)
“The strap’s paths between the effective safety-belt anchorage and the buckle are normally straight like the test bench specified in UN Regulation No. 129 (figure 1).”
“However, the strap’s paths between the effective belt-anchorage and the buckle of some vehicles in the market are not straight and are curved along the cushion (figure 2).”
When these paths are not straight, the occupants can be thrown forward significantly in a frontal impact accident. In a booster seat attached by ISOFIX, there are cases where the seatbelt will slip up to the neck and submarining will occur. This would increase the risk of injury to the neck and abdomen of a child occupant.
Sources (3)
“When the strap’s paths between the effective belt anchorage and the buckle are not straight, the occupants can be thrown forward significantly in a frontal impact accident.”
“If an occupant is seated in the booster seat attached by ISOFIX, there are cases where the seatbelt will slip up to the neck and submarining will occur”
“This would increase the risk of injury to the neck and abdomen of a child occupant.”
The proposal shows maximum 3 ms dummy chest acceleration for two types of Child Restraint Systems. With a buckle slack of 50 mm, the maximum chest acceleration in one Child Restraint System approached the criteria of UN Regulation No. 129. With a buckle slack of around 80 mm, the maximum chest acceleration exceeded these criteria. The increased slack also increased the passenger’s excursion, which is detrimental to occupant safety. The proposal therefore recommends limiting the slack of the buckle belt.
Sources (5)
“Figure 3 shows the relationship between the amount of slack in the buckle strap and the maximum 3 ms dummy chest acceleration for two types of Child Restraint Systems.”
“When the buckle slack was 50 mm (see the left graph of figure 3), the maximum chest acceleration in one Child Restraint System approached the criteria of UN Regulation No. 129.”
“When the buckle slack was around 80 mm (see the right graph of figure 3), the maximum chest acceleration exceeded the noted criteria.”
“The increased slack in the buckle belt increased the passenger’s excursion, which is detrimental to occupant safety”
“Therefore, we recommend limiting the slack of the buckle belt.”
Proposer's reason (informal document GRSP-76-32-Rev.1)
The proposal from Japan was held until the complex work to split Regulation R16 was finalised. Because of this time, its original 1 September 2026 transitional provisions would be applicable as soon as it was published. The outcome of an informal discussion of this concern was that OICA would produce an informal document requesting a 1-year delay, until 1 September 2027. The same date of September 2027 for new type approvals concerning the package of the 3 UN Regulations will facilitate the administrative work for homologation.
Submitted by Expert from OICA. Working party adoption: ECE/TRANS/WP.29/GRSP/76, para. 11.
Sources (4)
“Amendment GRSP/2024/23 from Japan, although agreed in principle at GRSP, was held until the complex work to split Regulation R16 was finalised.”
“The time taken to do this would result in the original 1 September 2026 transitional provisions of GRSP/2024/23 to be applicable as soon as it was published.”
“The outcome of this discussion was that OICA would produce an informal document requesting a 1-year delay to GRSP, until 1st September 2027.”
“In addition, the same date of September 2027 for New Type Approvals concerning the package of the 3 UNRs will facilitate the administrative work for homologation.”
Proposer's reason (informal document GRSP-76-32-Rev.1)
Appendix 3 only contains one table, referenced as “Table 1”. According to the proposal, paragraph 3.4. just clarifies that some parts of the Regulation are not missing.
Submitted by Expert from OICA. Working party adoption: ECE/TRANS/WP.29/GRSP/76, para. 11.
Source
“Appendix 3 only contains one table, referenced as “Table 1”; this paragraph just clarifies that some parts of the Regulation are not missing.”
Document trail
- 2024-09ProposalECE/TRANS/WP.29/GRSP/2024/23Proposal for the 01 series of amendments, submitted by the expert from Japan
- —Amended in sessionGRSP-76-32-Rev.1Revised proposal of the expert from OICA amending the proposal
- —Working party adoptsECE/TRANS/WP.29/GRSP/76Session report, para. 11 and Annex IV, section A
- 2025-04Sent to WP.29ECE/TRANS/WP.29/2025/47Text that GRSP adopted and 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.50.2026.TREATIES-XI.B.16.173UN depositary notification
Q3Who is affected
Vehicle manufacturer
- For rear seating positions of M1 category vehicles, meet paragraph 5.2.3.1. unless any condition of paragraph 5.2.3.2. is satisfied.
- Demonstrate the correlation between the actual vehicle and/or parts and the drawing or 3D data.
- Note that, from 1 September 2027, Contracting Parties need not accept preceding-series approvals first issued after that date.
Component supplier
- For M1 rear seating positions, note that paragraph 5.2.3.1. does not apply to a safety-belt assembly with a pre-loading device.
- For M1 rear seating positions, be ready for the Annex 7 buckle strap assembly test (paragraph 5.2.3.2., point (c)).
Technical service / Approval authority
- Be ready for the Annex 7 tensile test of the buckle strap assembly (paragraph 5.2.3.2., point (c)).
- Be ready to assess point (b) evidence of paragraph 5.2.3.2.: experimental data, simulation, or desktop strength calculations.
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ⓘ This report gives advice only. It is not legal or type-approval advice.