Non-collinear low velocity rear end collision human kinematics have not previously been studied. Occupant head and neck motions during 20 similar non-collinear (15 and 30 deg angle) left rear end collisions were analyzed for 5 male test subjects alternately positioned in the left and right front seats of the struck vehicle. Displacement-time and acceleration data for occupant, seat, and vehicles were determined by 3D motion analyses and linear accelerometer outputs. The dynamics of the struck vehicle at 6.0 to 9.3 kph (3.8 to 5.8 mph) delta-V showed an initial period of yaw, even when the rear tires did not lose traction with the pavement. The brief yaw seen during the 15 deg impacts was accompanied by early relative rightward movement of the vehicle's seat and seatback behind the stationary test subject. The subjects subsequently engaged the left region of the seatback and head restraint. A more pronounced yaw accompanied the loss of rear tire traction during the 30 deg tests, and resulted in occupant contact/loading further toward the left edge of the seat back and head restraint. For a given striking vehicle velocity, the impact severity in terms of head acceleration and changes in head velocity were significantly lower (p<0.05) at vehicle impact angles of 30 deg compared with 15 deg. Clinically, there were only minor short-term symptoms and no long-term symptoms observed in these angled impacts.
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