Lower Anchors and Tethers for Children (LATCH) was intended to standardize the attachment between child restraints and vehicle seats. However, vehicle manufacturers implement LATCH differently, resulting in wide variation in factors such as anchor accessibility and ease-of-attachment of child restraint connectors. Some of these variations may affect parents’ ability to correctly install child restraints. Identifying the characteristics of the vehicles with the best child restraint installations conducted by subjects can provide guidance for developing vehicle LATCH systems that increase the correct installation of child restraints. Methods: Characteristics of the LATCH systems and other relevant vehicle features were documented in 98 top-selling 2010-11 vehicle make/models. These features, in combination with proposed LATCH usability ratings and guidelines from the International Standards Organization and Society of Automotive Engineers, were used to select 12 vehicles for volunteer testing. These vehicles provided a range of LATCH system characteristics. Thirty-six volunteers were assigned to four study groups, with each group testing three vehicles, four child restraints (infant, rear-facing convertible, forward-facing convertible, and combination seat), and two installation methods (lower anchors and seat belt) in a split-plot experimental design. Mixed-effects logistic regression models were used to identify predictors of tight installation and correct use of lower anchors. The results from the vehicle survey indicated that most vehicle manufacturers provide LATCH hardware at the minimum number of locations required by regulation. In the 21 vehicles with a third row, four had no tether anchors and 11 had no lower anchors in the third row. Only 16 vehicles allowed use of LATCH in the second row center seat with dedicated lower anchors (7) or anchors borrowed from the outboard seats (9).Study volunteers correctly used the lower anchors in 60 percent of LATCH installations and used the upper tether in 48 percent of forward-facing installations. When the tether was used, it was used correctly in 46 percent of these installations, or 22 percent of all forward-facing installations. Only 13 percent of all trials resulted in completely correct child restraint installation with correct use of lower anchors or seat belt, correct use of tether anchor, tight seat installation, and correct installation angle. Tight installation was 3.3 times as likely when the lower anchors were used correctly compared with trials when they were not used correctly. Three lower anchor characteristics were associated with rates of correct lower anchor use of more than 50 percent: clearance angle around the lower anchors greater than 54 degrees, attachment forces less than 40 pounds, and anchor depth within the seat bight of less than 2 cm. Vehicles meeting all three criteria were 19 times as likely to have lower anchors used correctly compared with vehicles meeting none of the criteria. No vehicle features predicted either use of tethers or correct use of tethers, although the ability to identify important features of tether anchors was limited due to the low use of tethers. Vehicle LATCH systems that improve lower anchor accessibility and ease-of-attachment of child restraint connectors could increase the rate of correct lower anchor use, but more research is needed to understand the factors associated with tether use and use that is correct. (Author/publisher)
Samenvatting