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Factors affecting tether use and misuse

This project investigated factors relating to tether use and misuse. Volunteer testing was performed with 37 subjects on 16 different vehicles using 2 forward-facing child restraints (Britax Marathon 70 or the Evenflo Triumph), with each subject performing 8 child restraint installations on a set of four vehicles. Vehicles were selected to provide a variety of general tether locations (filler panel, upper seatback, lower seatback, floor, or roof), as well as a variety of recommended tether routings with respect to the head restraint: under, over, around. Simple instruction regarding the LATCH system was provided after the fourth trial. Subjects used the tether in 89% of the 294 forward-facing trials and attached the tether correctly in 57% of installations. Subjects were more likely to use the tether if they were less than age 40, had previous tether experience, if the tether was located on a filler panel, and if the vehicle did not have any potentially confusing hardware. In addition, tether use was 83% in the first four trials and increased to 95% in the last four trials after instruction was provided. Subjects had the greatest difficulty in the pickup truck, which use loops of webbing as a router for the installed position and the tether anchor for the adjacent position; the tether was attached correctly in only 11 percent of installations. Tethers were more likely to be used when the tether anchor was located on the filler panel of sedans, which had a use rate of 95 percent, compared to when the anchor was located on the floor, roof, or seatback, which had use rates ranging from 79 to 89 percent. Tethers were less likely to be attached correctly when there was potentially confusing hardware present, 47 percent, compared to 70 percent. In addition, tether anchors located on the filler panel or mid seatback had higher rates of correct attachment, 60 and 69 percent , respectively, than those on the floor, roof, or lower seatback, which all had correct attachment rates lower than 50 percent . No vehicle tether hardware characteristics or vehicle manual directions were associated specifically with correct tether routing and head restraint position. Installations involving the single tether strap were 10 times as likely to have the tether attached correctly and 1.7 times as likely to be routed correctly and have the head restraint positioned correctly, compared with installations with the v-shaped tether. Lack of instruction in most vehicle owner’s manuals regarding the routing of a V-style tether more challenging to use. With the single strap-style tether, it was more straightforward to have the tether strap flat and pull it tight, as well as to route it as directed. With the V-style tether, the adjustment hardware was often located underneath or close to the head restraint when installed in the vehicle, making it difficult to tighten. Recommendations to reduce tether misuse include labeling tether anchors, eliminating confusing hardware, allowing any head restraint position (including removal), providing instruction for routing V-style tethers, allowing options in tether routing, and redesigning tether anchors/routers found in pickup trucks.

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