Rollover crashes are generally less lethal than head-on and side impact collisions, provided the individual is not ejected or the vehicle rolls into an unyielding object such as a tree. Anything that prevents ejection of an occupant increases the probability of survival. Because of better design, present-day car doors usually do not open in rollovers. Instead, the unrestrained individual is ejected out the window. Thus, use of a seat belt is very beneficial in such accidents. If one is not wearing a seat belt, one may be thrown about the passenger compartment like a rag doll and not infrequently ejected from the vehicle. Ejection may be complete with the car rolling over the ejected individual, or just the head and upper trunk may protrude to be rolled over by the vehicle. The body may then pop back into the car. It is not uncommon in rollover accidents to see a blood-stained depression in the roof of the car adjacent to a window (Figure 9.9). The head of one of the individuals in the vehicle has protruded through the window as the car rolled over, with the head causing the depression as it was crushed. Paint from the roof is sometimes left on the head of the victim in such instances.
The injury patterns in rollover accidents in which an individual is not restrained are much more variable because the individual is thrown about, impacting surfaces willy-nilly. There is no specific injury pattern. If the individual is ejected and the car rolls over his trunk but not his head, there may be no external evidence of trauma (Figure 9.10). Subsequent autopsy, however, can reveal massive ruptures of the lungs, heart, liver, spleen, and mesentery.
Rollovers account for approximately 18.8% of all fatal motor vehicle accidents.3 In passenger cars, crash direction is most commonly from the front, with rollovers accounting for 15.1% of fatal accidents. In contrast, rollovers account for 36% of fatal crashes involving utility vehicles; 24.5% for pickups; 20.3% for vans and 13.8% for large trucks. 3
Most single-vehicle rollover accidents involve a vehicle's running off the roadway, followed by an abrupt attempt to steer it back onto the road. The attempted correction causes the vehicle to skid sideways. As it does, it begins to tip over toward the leading side. If there is sufficient lateral momentum, the tires will plow into the surface and the vehicle will roll over. If the momentum is insufficient, the vehicle will fall back onto its wheels. The point at which the vehicle begins to roll over is approximately where the tire marks stop. The propensity of the vehicle to tip is determined not only by the side momentum but also by the height of the vehicle's center of gravity (thus, the increased tendency of utility vehicles to roll over) as well as the nature of the ground surface. A vehicle is more likely to roll over on dirt than pavement.
As a vehicle begins to roll, it becomes airborne. With a low center of gravity, such as in automobiles, the rolling vehicle tends to land on the edge of the roof opposite to the side of the car that is leading the rollover. In vehicles with a high center of gravity, such as utility vehicles, the impact point is more likely to be the leading edge of the vehicle roof. After impact, the vehicle continues to roll, often coming to rest back on its wheels. When a
vehicle does roll over, it usually doesn't do it more than once. By studying the scene and the vehicle, an accident reconstructionist can estimate the speed of the vehicle at the time of rollover, the number of rolls, the impact points on the vehicle, and the direction of the roll.
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