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.

BS ISO 13216-4:2020

Road vehicles. Anchorages in vehicles and attachments to anchorages for child restraint systems - Lower tether anchorages

Current, Under Review

Published:

30 Nov 2020