Usability and Compatibility

As implementations of LATCH hardware in vehicles and on child restraints have evolved over the past decade, problems with incompatibilities between vehicles and child restraints remain. Caregivers also make mistakes when securing their children in the child restraint harness. Several different rating systems have been proposed to improve the usability of child restraints, reduce misuse, and increase compatibility between the child restraint and vehicle.

NHTSA developed an Ease-of-Use (EOU) Rating system (NHTSA 2006) to provide consumers with information about which child restraints have features that enhance usability. The system has provided strong incentives for child restraint manufacturers to improve products, labeling, and instruction manuals with respect to usability. The rating system includes questions that address each child restraint area related to the most common misuse modes.

In the field, some misuse modes arise from features and elements of the vehicle environment and others result from interactions between specific child restraint and vehicle combinations. In 2015, the Insurance Institute for Highway Safety began to include LATCH usability ratings as part of their vehicle rating systems. Their ratings were based on research showing that having lower anchors less than 2 cm within the bight, a clearance angle of at least 54 degrees, and an applied force less than 40 pounds resulted in much higher rates of correct LATCH use (Jermakian et al. 2014, Klinich et al. 2013a, 2013b, 2014). These publicly available ratings have led to easier-to-use LATCH hardware in vehicles. NHTSA has proposed changes to FMVSS No. 225 to make usability a requirement, but the changes have not yet been finalized.

A usability rating scheme has been issued by the ISO Child Restraints Group that has rating forms for all three elements: the child restraint, the vehicle, and specific combinations of the two (ISO 2010, Pedder and Hillebrandt 2007). This rating system currently focuses on ISOFIX (LATCH-type) systems. Some of the vehicle features that are rated in the current version of the ISO document include the vehicle owner’s manual instructions on how to identify the number and location of seating positions available for child restraint installation, the visibility and labeling of the LATCH anchors, the presence of other hardware elements that could be mistaken for LATCH anchors, the actions required for preparing the seating position for child restraint installation, and conflicts between LATCH and seatbelts.

The SAE Children’s Restraint Systems Standards Committee has drafted a recommended practice to improve compatibility between child restraints and vehicles during LATCH installations (SAE 2009). Several of the procedures were the basis for the evaluations used in the IIHS ratings.