Effects of vehicle features on CRS installation errors

Abstract

This report documents a study of how vehicle features contribute to CRS installation errors. Thirty-two subjects were recruited based on their education level (low or high) and experience with installing CRS (none or experienced). Each subject was asked to perform four child restraint installations in three vehicles. Each subject first performed a CRS installation with a seatbelt in one vehicle, followed by three CRS installations using LATCH, one in each of three vehicles. One child restraint with a hook-on LATCH connector and one with a push-on LATCH connector were used. All installations were forward-facing, using an 18-month-old CRABI anthropomorphic test device (ATD). Six vehicles were used in testing, with half of subjects testing with each vehicle. Conditions were selected to provide a range of LATCH locations (visible, above seating surface, buried in bight), buckle stalk types (webbing vs. rigid), and tether locations (package shelf vs. seatback). After each installation, the experimenter evaluated 28 factors for each installation (such as tightness of installation, tether tightness, and LATCH belt attached correctly). Analyses used linear mixed models to identify the CRS installation outcomes associated with vehicle features. For LATCH installations, vehicles requiring higher forces to attach connectors to lower anchorages were more likely to be attached incorrectly. Vehicle seats with a bightline waterfall (which places the lower anchorage above the seating surface) increased rates of tight CRS installation for both seatbelt and LATCH installs. Seatbelt installations were tight (and locked) more frequently when the buckle stalk was located close to the bight rather than further forward. Subjects used the tether correctly in 30% of installations. Subjects used the tether more frequently during LATCH installations compared to seatbelt installations. The tether was used more frequently in sedans (with anchorage locations on the package shelf) than in vehicles with the tether anchorage located on the seatback. However, when the tether was used, it was routed correctly more often in vehicles with the tether anchorage on the seatback. A tether wrap around distance of 210 mm was sufficient to allow tightening of the tether with the two CRS tested, but additional testing showed that 5/16 CRS could not be tightened sufficiently with this wrap around distance. Installation time decreased with successive trials, but installation time was longer when subjects used the vehicle or CRS manuals. Subjects used the vehicle manual in 38% of installations, and were more likely to do so when the tether anchorage was located on the vehicle seatback. Subjects used the CRS manual in 88% of installations. In questionnaire responses, subjects indicated that the head restraints affected installations, and vehicle manuals varied in their ease of understanding. They also noted that tether anchorages on seatbacks were more difficult to locate than those on the package shelf. Results from this study do not fully support SAE and ISO recommendations for LATCH usability in vehicles. Recommendations are