The Characterization of Longitudinal Lumbar Acceleration in Low-Speed Rear-End Impacts Across Different Surrogate Occupant Types

Longitudinal lumbar acceleration is often overlooked as a key variable when biomechanically assessing lumbar response in rear-end collisions. The objective of this study is twofold: (1) to conduct a comprehensive literature review of peak longitudinal lumbar acceleration to statistically evaluate differences between three surrogate occupant types: human volunteers, post-mortem human subjects (PMHS), and anthropomorphic test devices (ATDs) and (2) to construct a mathematical predictive model of longitudinal lumbar acceleration using peak longitudinal vehicle or sled change in velocity (delta-V) and vehicle acceleration in rear-end impacts. Peak longitudinal lumbar acceleration was obtained from peer-reviewed literature and the Insurance Institute for Highway Safety database. Tests included belted human volunteers, PMHS, and ATD occupants seated upright in unmodified, conventional driver seats. Compared to human volunteers instrumented at L5-S1, BioRID ATDs instrumented at L1 displayed greater ratios of longitudinal lumbar acceleration to delta-V, but lower ratios when normalized by vehicle acceleration. Accelerometer placement, crash severity, test configuration and pulse duration across surrogate occupant types were found to influence overall lumbar response, relative to vehicle acceleration and delta-V. Regressions for human volunteers indicated positive relationships for longitudinal lumbar acceleration with respect to vehicle acceleration (R2 = 0.93, p<0.001) and all surrogate occupant types for vehicle delta-V (R2 = 0.96, p<0.001). Longitudinal lumbar acceleration was highly correlated to vehicle delta-V in both human volunteers and BioRID ATDs and was sensitive to crash severity and vehicle crash parameter choice (vehicle acceleration vs. delta-V). Close alignment was found between L1 BioRID ATD and L5-S1 human volunteer longitudinal accelerations at vehicle delta-Vs ≤ 14.3 km/h, suggesting that BioRID ATDs at L1 can reasonably replicate human lumbar response at L5-S1 within this crash severity range. This study quantified differences in longitudinal lumbar acceleration across occupant types in rear-end collisions and developed surrogate-specific and cumulative models for prediction of longitudinal lumbar acceleration from delta-V.