Human Occupant Motion in Rear-End Impacts: Effects of Incremental Increases in Velocity Change 2001-01-0899

Interest in the mitigation of whiplash associated disorders (WAD) has increased in priority over the last 10 years, and an increasing number of human subject rear-end collision tests have been conducted to assist in the understanding of WAD. Traditionally this testing has examined the effects of variations in occupant characteristics (age, height, gender, etc.), seat characteristics (geometrical and constitutive), and impact severity. This data has resulted in advancements in the understanding of WAD and has provided occupant performance corridors at specific velocity changes, however no controlled study has examined the singular effect of incremental velocity change increases on occupant kinematics. Moreover, while vehicle velocity change is typically employed as a singular measure of impact severity, it is of interest to examine whether this or other impact-related parameters, such as energy or acceleration, are also correlated with occupant kinematics.

A series of five instrumented human subject rear-end impact tests were conducted to monitor the effects of increasing impact severity on occupant motions and forces. A female subject who approximated the stature of a 50^Th percentile (“average”) female participated in the study. Impact speeds were selected such that the stationary target vehicle experienced velocity changes of 1.6, 3.2, 4.8, 6.4 and 8 km/h (1 to 5 mph). A minivan was the target vehicle and the minivan's original unmodified driver's seat and seat belt were used for all tests. Accelerometers were affixed to both the target vehicle and human subject. The subject's motions during impact were recorded by an onboard high-speed digital video camera.

Target vehicle Delta V, average vehicle acceleration, peak vehicle acceleration, and vehicle kinetic energy change were evaluated for their influence on various occupant response parameters. Occupant parameters which have been suggested to be associated with WAD causation in prior literature were selected. All of the vehicle parameters correlated well with relevant maximal head and torso accelerations; head, torso and knee rearward (-X) displacements; head and torso upward (+Z) displacements; and neck injury criteria (NIC) (p<0.05). Average vehicle acceleration, peak vehicle acceleration, and vehicle kinetic energy proved only slightly better predictors for maximum head and torso accelerations than Delta V.