Guidelines for Implementation of the Child Restraint Anchorage System or LATCH System in Motor Vehicles and Child Restraint Systems
These guidelines should be considered:
When implementing the LATCH system in vehicle seating positions that will be designated by the vehicle owner’s manual and in the information included in the owners manual.
When implementing the LATCH system in child restraint designs that include the LATCH system and in the information included in the instruction manual
The Children’s Restraint Systems Standards Committee has prepared an SAE Recommended Practice which provides guidelines to motor vehicle manufacturers for certain characteristics of vehicle lower and upper (tether) anchorages for child restraints, and to child restraint system (CRS) manufacturers for corresponding features of CRS lower and tether attachments, so that each of their products can be made more compatible with the other.
In the course of the implementation of LATCH (Lower Anchorages and Tethers for CHildren) in the United States and LUAS (Lower Universal Anchorage System) in Canada, it is apparent that there are incompatibilities between vehicle anchorage and child restraint attachment features. These incompatibilities have been reported by individual owners of CRS, and by child passenger safety technicians certified by the National Highway Traffic Safety Administration (NHTSA) Standardized Child Passenger Safety Training Program, and are summarized below.
Access to vehicle anchors for CRS attachment connectors is sometimes made difficult by vehicle seat back or cushion soft trim or structure adjacent to the anchors. In some instances, installers have inadvertently engaged the connectors with seat construction features, such as reinforcement wires, instead of the anchor bar. Further, seat back stiffness may not allow non-rigid attachment connectors to rotate upward to properly align with webbing, which can influence webbing tension and sometimes result in seat back damage. Add-on alignment devices (“funnels”) must assist rather than impede access to the anchor bars.
Vehicle anchor bar co-linearity is not well defined in the Federal standards requiring lower anchorages, which can lead to problems with installing CRS with rigid attachments. An anchorage co-linearity guideline is desirable.
Where seat cushions are deeply recessed or dished, anchor bars are sometimes located well above the seat cushion surface in order to meet the child restraint fixture attitude requirement. As a result, CRS’s with narrow bases rest on the cushion surface, and installers find that the CRS belt path openings or webbing attachment points are so close to the anchor bars that the webbing cannot be tightly adjusted. A limit to the distance from the cushion surface to the anchor bars is indicated to allow CRS manufacturers to design for this circumstance.
Lower anchorages are seldom provided for center rear seating positions. However the inboard anchor bars are often identified by vehicle manufacturers as suitable for use with CRS with non-rigid attachments, provided that the CRS manufacturer supports that application. In order to implement that use, the installer must be made aware of that fact in the vehicle owner’s manual and must know the spacing of the inboard anchor bars.
Corresponding to the vehicle seat and anchorage issues above are child restraint system lower and tether attachment issues. CRS attachment connectors are sometimes difficult to engage or be disengaged from vehicle anchor bars because of their size or configuration.
Further, the end of the connector of a non-rigid attachment engaged with an anchor bar must allow the rotation of the connector upward to align with the webbing of the attachment.
There must be a limit to the assembled length of the non-rigid attachment connector and adjuster to assure the use of the CRS in the range of seat and anchorage configurations in the marketplace. Installers have also reported of top tether connectors with built-in adjustment features loosening due to positioning and angle of webbing when used with some tether anchors located under vehicle seats.
Installers have reported that it is difficult to assure that connectors are securely engaged with anchor bars without a visible or audible indication of that engagement. Further, connectors must be provided with a feature that assures that the devices are engaged, and that requires an overt action to disengage them. Non-rigid attachment connectors must be provided with a storage location on the CRS to minimize the potential for injury from an unsecured connector in the event of a collision.
If CRS’s are intended for use in center rear seating positions with other than standard anchor bar spacing where supported by the vehicle manufacturer, the installer must be made aware of that fact in the CRS instructions and must be made aware of the allowable range of anchor bar spacing.
With regard to tether straps, installers indicate that they should be adjustable so as to be used with anchorages in the range of locations allowed in the Federal rules. Further, the CRS should have provision for storing the tether strap assembly.
Although NHTSA has proposed to update FMVSS 225 in order to address improvements of LATCH accessibility and usability, some issues remain of importance in order to improve compatibility.