Subject Evaluation of Devices Intended to Reduce Risk of Seatbelt Entanglement

Abstract

Since 2000, there have been over 200 incidents reported where a rear seat occupant became entangled in the seatbelt when they inadvertently switched it from emergency locking mode (ELR) to automatic locking mode (ALR). While a method is needed to lock the seatbelt when using it for child restraint system (CRS) installation, the National Highway Traffic Safety Administration (NHTSA) commissioned tool, inc. to develop prototype devices that could reduce the risk of seatbelt entanglement resulting from the lockability requirement. The purpose of this study is to perform testing with volunteer subjects to evaluate these prototype devices in comparison to standard seatbelt system by assessing how different designs would be used to install CRS, the quality of the resulting installations, how users would disentangle a trapped child surrogate, as well as to identify volunteer experience when using the belts themselves. Four prototype devices were evaluated in two phases of testing. In phase 1, D1, D2, and D3 were compared to standard seatbelt and LATCH using two forward-facing and two rear-facing CRS. In phase 2, D1 and D4 were compared to standard seatbelt using three forward-facing CRS. Phase 1 tested 16 subjects while Phase 2 tested 24. Subjects were recruited to include men and women of different ages with and without previous CRS installation experience; phase 1 also included education level as a criteria, while phase 2 included subject size. After the first installation trial using each device, the subject was presented with a crash dummy entangled in same device belt system, and instructed to free the dummy. In phase 2, subjects also participated in “comfort” trials where they sat in the vehicle seat, donned the seatbelt, and performed a reaching task intended to trigger a nuisance locking scenario. All four prototype devices had shorter disentanglement times than trials with the standard seatbelt, but there was not a statistically significant difference between the devices. There were no substantial differences in the quality of child restraint installation among the prototype devices. In phase 2, subjects viewed video instructions midway through the installation trials, which had a strong effect on reducing installation errors. In nuisance locking trials, subjects with higher BMI or taller stature were most likely to experience unintended seatbelt locking while performing a reach task.