ISO 13216-4:2020

Road vehicles - Anchorages in vehicles and attachments to anchorages for child restraint systems - Part 4: Lower tether anchorages

This document establishes the positioning zones, dimensions and general and static strength requirements for lower tether anchorages. Lower tether anchorages can be used together with seat bight anchorages according to ISO 13216-1, or with other methods for anchoring child restraint systems (CRS) in road vehicles. This document is applicable to all seating positions, intended by the vehicle manufacturer, for use with rearward-facing CRSs. These seating positions can include outer and mid positions in rear seats (second and third row), as well as the front passenger seat. This document also specifies requirements and strength testing of retrofit lower tether anchorages.

Véhicules routiers — Ancrages dans les véhicules et attaches aux ancrages pour systèmes de retenue pour enfants — Partie 4: Ancrages pour fixation des sangles inférieures

General Information

• Status: Published
• Publication Date: 26-Oct-2020
• ICS: 43.040.80 - Crash protection and restraint systems
• Technical Committee: ISO/TC 22/SC 36 - Safety and impact testing
• Drafting Committee: ISO/TC 22/SC 36/WG 2 - Child restraint systems
• Current Stage: 9020 - International Standard under periodical review
• Start Date: 15-Oct-2025
• Completion Date: 15-Oct-2025

Overview

ISO 13216-4:2020 specifies requirements for lower tether anchorages (LTA) used to attach lower tethers for rearward-facing child restraint systems (CRS) in road vehicles. The standard defines positioning zones, dimensional and installation requirements, general and static strength requirements, and requirements for retrofit LTAs. It is intended to improve usability, reduce misuse and vehicle interior damage, and increase safety by standardizing pre‑installed lower tether anchorages for rearward-facing CRSs.

Key Topics

• Scope and applicability
  • Applies to all vehicle seating positions intended by the manufacturer for rearward-facing CRSs (outer and mid rear seats, third row, and front passenger seat).
  • Covers both factory-installed LTAs and mounting points for retrofit installations.
• Positioning and reference method
  • Positioning zones are defined relative to the ISO/R2 envelope (installed with seat adjusted to its rearmost position); Annex A provides a procedure for non‑ISOFIX positions.
  • If two LTAs are used per CRS position, minimum separation is 280 mm; they must not be on the same side of the envelope centreline and the offset between centrelines shall not exceed 200 mm.
  • If a single LTA is used it must be symmetrically positioned within ±50 mm of the envelope centreline.
  • Rearmost surface of the zone is positioned 100 mm rear of a vertical plane through the ISO/R2 reference point.
• Dimensions and design
  • Anchorages must provide openings/clearance (square, circular or semi‑circular) compatible with standard top tether connectors per ISO 13216-2.
  • LTAs should be shaped to minimize injury risk (no sharp edges/protrusions).
  • LTA placement must avoid common support‑leg zones and allow practical routing without damaging interior components.
• Strength and testing
  • Strength testing considers a CRS plus child total mass up to 40 kg.
  • If the LTA is attached to vehicle parts already approved under relevant regulations (examples include UN R14, FMVSS 207, etc.), additional strength requirements may be deemed satisfied.
  • Annex B details requirements and testing for retrofit LTAs.
• Instructions and marking
  • Clause 6 sets requirements for user instructions and marking to support correct use.

Applications

• Vehicle manufacturers: design and integrate LTAs into new vehicles and prepare mounting points for retrofit kits.
• CRS manufacturers: design tether connectors and test compatibility with LTA zones and dimensions.
• Test laboratories and regulators: perform LTA strength testing and conformity checks.
• Aftermarket installers and OEM service teams: install retrofit LTAs to the Annex B criteria.

Related Standards

• ISO 13216-1 (ISOFIX seat bight anchorages)
• ISO 13216-2 (Top tether anchorages and attachments)
• ISO 13216-3 (CRS classification and vehicle space)
• Referenced vehicle structural/regulatory frameworks (e.g., UN regulations, FMVSS) for existing type‑approval strength criteria

Keywords: ISO 13216-4:2020, lower tether anchorages, LTA, child restraint systems, CRS, ISOFIX, retrofit anchorages, tether strength testing, vehicle safety.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 13216-4
First edition
2020-10
Road vehicles — Anchorages
in vehicles and attachments to
anchorages for child restraint
systems —
Part 4:
Lower tether anchorages
Véhicules routiers — Ancrages dans les véhicules et attaches aux
ancrages pour systèmes de retenue pour enfants —
Partie 4: Ancrages pour fixation des sangles inférieures
Reference number
©
ISO 2020
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
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ISO copyright office
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Published in Switzerland
ii © ISO 2020 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Dimensions and installation requirements . 2
4.1 Description and applicability of lower tether anchorages or LTA mounting points . 2
4.2 Positioning of lower tether anchorages. 2
4.3 Lower tether anchorage design . 5
5 Lower tether anchorage strength requirements and testing . 5
5.1 Strength test method . 5
5.2 Strength requirements . 7
6 Instructions and marking . 7
Annex A (normative) ISO/R2 positioning procedure for non-ISOFIX seat position .8
Annex B (normative) Requirements and testing of retrofit lower tether anchorages .9
Annex C (informative) Example LTA installations .12
Annex D (informative) Example from seat track survey of 24 cars .15
Bibliography .17
Foreword
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different types of ISO documents should be noted. This document was drafted in accordance with the
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iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 22 Road vehicles, Subcommittee SC 36
Safety and impact testing.
A list of all parts in the ISO 13216 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved

Introduction
Lower tether anchorages (LTA), for rearward facing child restraint systems (CRSs) in passenger cars,
are used to enhance protection of children in cars. The lower tethers help to reduce CRS rotation in rear
impacts, during the rebound phase in frontal impacts, and in rollover events. Lower tethers, attached
to the LTA, may be used together with seat bight anchorages according to ISO 13216-1 (ISOFIX), or with
other methods for mounting rearward facing CRS in road vehicles, mainly using the vehicle seat belt.
In line with ISOFIX, standardization of LTA enables pre-installed anchorages with adequate performance
within a designated zone. Pre-installed anchorages will improve the usability and reliability of attaching
the lower tethers. In addition, having dedicated anchorages reduces the risk of tethers routed in a way
that can damage the car interior, seat chassis, cables under the seat, etc.
Dedicated pre-installed anchorages will ensure ease-of-use, reduce risk of misuse and simplify
the mounting of a rearward facing CRS. With the use of lower tethers and specified LTA and tether
connectors (click-in function in analogy with ISOFIX connectors) the CRS can be easily attached.
This document provides requirements and guidelines to facilitate the introduction of lower tether
anchorages in passenger cars contributing to ease-of-use, reduction of potential damage to vehicle
interior, and increased safety by facilitating increased use of rearward facing CRSs.
Background
Rearward facing CRSs have been available on the market since late 1960s and are used for infants as
well as toddlers. In the Nordic countries, they have been used since their introduction as the main CRS
for children up to approximately four years of age and have provided evidence of excellent occupant
protection.
Most of the large rearward facing CRSs use lower tethers, which are attached to the floor area or seat
in front of or below the seating position of the CRS. There is more than 40 years of experience of lower
tether usage. Some cars have pre-installed anchorages in which the lower tethers can easily be attached.
The most common positions of the anchorages are on the seat rails in front of the CRS (inside, outside,
or end of seat rails), but alternative placements are also used.
However, the majority of the vehicles have no pre-installed anchorages, as a consequence the tethers
are instead routed around the seat chassis, the seat cushion or other parts that can be accessed.
The primary attachment of the rearward facing CRS is the ISOFIX or the vehicle seat belt. In addition, a
support leg is usually used together with the lower tethers. An alternative to the lower tether is to use
a bar pressed against the vehicle seat backrest (so-called rebound bar). The rebound bar provides some
effect to reduce rotation in rear-end impacts and the rebound phase in frontal impacts, however it is
not sufficient for the large rearward facing CRSs, especially when attached using the vehicle seat belt.
The lower tethers also provide superior protection in rollover or turnover events.
INTERNATIONAL STANDARD ISO 13216-4:2020(E)
Road vehicles — Anchorages in vehicles and attachments
to anchorages for child restraint systems —
Part 4:
Lower tether anchorages
1 Scope
This document establishes the positioning zones, dimensions and general and static strength
requirements for lower tether anchorages.
Lower tether anchorages can be used together with seat bight anchorages according to ISO 13216-1, or
with other methods for anchoring child restraint systems (CRS) in road vehicles.
This document is applicable to all seating positions, intended by the vehicle manufacturer, for use with
rearward-facing CRSs. These seating positions can include outer and mid positions in rear seats (second
and third row), as well as the front passenger seat.
This document also specifies requirements and strength testing of retrofit lower tether anchorages.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 13216-2:2004, Road vehicles — Anchorages in vehicles and attachments to anchorages for child
restraint systems — Part 2: Top tether anchorages and attachments
ISO 13216-3, Road vehicles — Anchorages in vehicles and attachments to anchorages for child restraint
systems — Part 3: Classification of child restraint system and space in vehicle
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13216-2 and ISO 13216-3, and
the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
lower tether anchorage
LTA
anchorage on the vehicle seat track or on or close to the vehicle floor to which a lower tether (3.4) can be
attached
[SOURCE: ISO 29061-1:2010, 3.15, modified — The term "rebound tether anchorage" has been deleted
and the phrase "rebound tether" has been deleted in the definition before "lower tether".]
3.2
retrofit lower tether anchorage
retrofit LTA
lower tether anchorage (3.1) for after-market installation in the vehicle
Note 1 to entry: Retrofit LTAs can be provided by OEMs or CRS manufacturers.
3.3
LTA mounting point
mounting point prepared by the vehicle manufacturer for installation of retrofit LTA (3.2)
3.4
lower tether
type of anti-rotational device intended to restrict the rearward rotation of a rearward-facing CRS
Note 1 to entry: It usually comprises a tether strap or other hardware attached near the back or base of the
CRS that connects to a lower tether anchorage. It incorporates a device to enable it to be connected to such an
anchorage.
[SOURCE: ISO 29061-1:2010, 3.14, modified — The term "rebound tether" has been deleted.]
4 Dimensions and installation requirements
4.1 Description and applicability of lower tether anchorages or LTA mounting points
Lower tethers are used to increase installation stability and to reduce rotation in a rear impact as well
as rebound effects in a frontal impact. The usability and reliability of lower tether attachments can be
greatly improved when lower tether anchorages are pre-installed in the vehicle.
Lower tether anchorages for rearward facing CRSs are similar to, and for most aspects comparable to,
the top tether anchorages for forward facing CRSs.
The most common positions of lower tether anchorages are on the seat rails in front of the CRS (inside,
outside, or end of seat rails), but alternative methods are also used. For most vehicles it is relatively
easy to introduce lower tether anchorages, since there are already seat rails or other appropriate
structures available in the applicable zones. Example installations are shown in Annex C. A summary of
the background feasibility study is given in Annex D.
The requirements and guidelines of this document are intended to facilitate the introduction of lower
tether anchorages in vehicles.
The specifications apply to completely installed LTAs by the vehicle manufacturer and to mounting
points prepared for the installation of retrofit LTAs. To ensure sufficient strength of retrofit LTAs, the
specifications given in Annex B shall be followed.
The installation requirements in 4.2 and the dimension requirements in 4.3 also apply to retrofit LTAs.
4.2 Position
...