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Rollover collisions are very complex and the subject of significant interest. Roll-over collisions involving Sport Utility Vehicles (SUV) are of particular interest due to their high center of gravity (increased propensity for rollover) and recent surge in popularity. The following research examines SUV rollover collisions documented in the National Automotive Sampling System (NASS) Crashworthiness Data System (CDS) for the years 1998 through 2004. The NASS/CDS was initially screened for SUV rollover collisions, then screened to eliminate soft top vehicles, such as the Jeep Wrangler and Suzuki Samurai. The injury data was further limited to driving age teens and adults (age 16 and older) in the front outboard seating positions.

Four full scale vehicle rollover tests, about the roll axis (X-axis), were staged using a sled attached to a large truck. Each vehicle was fitted with a nine-accelerometer array that approximated the center of gravity and two single axis accelerometers attached to the roof adjacent to the A-pillar/roof junction. The acceleration data was retrieved for three tests; however, the data recorder malfunctioned on the remaining test. Data was collected at 1000 hertz and processed to determine the linear and rotational acceleration with respect to each of the three vehicle coordinate axes. Rollover video and scene data were also collected to correlate vehicle rollover motion with the accelerometer data.

Seventeen rear-end impacts with a nominal 8 km/hr change in velocity to five human subjects in four positions were conducted. The four seated positions consisted of the Normal position, with the torso against the seat back, looking straight ahead, hands on the steering wheel, and feet on the floor; the Torso Lean position, with the torso leaned forward approximately 10 degrees away from the seat back; the Head Flex position, with the head flexed forward approximately 20 degrees from normal; and the Head Flex / Torso Lean position, with the head flexed forward approximately 20 degrees from normal and the torso leaned forward approximately 10 degrees from normal position. Relative to the Normal position, it was found that in both positions involving the torso lean, the peak head acceleration for the subject's head was reduced during the head-restraint impact.

The equations of rotational motion used to calculate pre-impact vehicle speeds using the rotational displacement of the vehicles following a collision are well known. The technique uses the rotational momentum exchange during impact and the principle of conservation of rotational energy to calculate the post impact vehicle angular velocity from the energy dissipated during the vehicle's rotation to a stop (product of torque and rotational displacement). Integral to the calculation of the stopping torque on the vehicle is the determination of the effective rotational coefficient of friction (fr) between the tires and the roadway. The interactions of the road with the tires to produce the rotational coefficient of friction (fr) are more complex and less understood than those of linear coefficient of friction (deceleration factor). A derivation of the post impact equations of motion and the kinematics of vehicles in rotation are examined.