Effect of Cognitive Workload on Automatic Restraint System Usage 2000-01-0174

This exploratory study investigated the effect of cognitive workload on manual lap belt usage in automatic restraint systems consisting of a passive motorized shoulder belt and a separate manual lap belt. Previous observational studies showed that, while these types of passive automatic restraint systems increased shoulder belt usage, occupants frequently did not engage the manual lap belt. This omission put the occupants at a significantly increased risk of injury in a crash. These studies also suggest that forgetfulness was one of the main reasons that occupants did not engage the manual lap belt. The objective of this study was to quantify manual lap belt usage with this type of automatic restraint system under varying cognitive workloads. Ten subjects participated in two testing sessions consisting of a low and high cognitive workload. During each test session, the subjects drove around a pre-defined course where they exited the vehicle at five locations to perform specific tasks. This presented each subject with six opportunities during each test session (start plus five stops) to engage the manual lap belt. Tasks for the second test session were designed with a much higher cognitive workload. Results showed that two out of ten subjects and six out of ten subjects did not engage the lap belt at least once for both the low and high workload, respectively. Overall, six subjects did not engage the lap belt at least once across all tests. Of sixty total opportunities to engage the lap belt in each workload condition, the subjects did not engage the manual lap belt seven for the low workload and fourteen times for the high workloads. Overall, subjects were 2 to 3 times more likely not to engage the lap belt under the higher workload test condition. Statistical analysis did not detect any statistically significant differences in belt usage between workloads, but the data suggests a trend for decreased lap belt usage as the workload increased. Safety issues regarding automatic restraint systems are also discussed.