Rollover

A rollover collision is a complex sequence of events occurring at high velocity (>65 km/h or 40 mph) and is usually precipitated by a loss of control (656). There are different types of rollover collisions (657):

• Trip-over. This is the most common type. The lateral motion of a vehicle is suddenly slowed as the vehicle's wheels contact a surface (e.g., gravel).

• Fall-over. The center of gravity of a vehicle causes it to tilt down a slope.

• Flip-over. The vehicle's side is lifted by an elevated surface (e.g., guardrail).

Fig. 68. Rollover; partial ejection of driver and head contact with edge of roof. Blood on roof (arrow). (Courtesy of Road Safety and Motor Vehicle Regulation Directorate, Transport Canada.)

• Climb-over. The vehicle actually passes over a fixed object (e.g., guardrail).

• Bounce-over. The vehicle rebounds off a fixed object.

• Turnover. Centrifugal forces on a sharp turn or rotation, particularly when the vehicle has a high center of gravity, causes tilting.

• Collision with another vehicle.

During vehicle rollover, kinetic energy is dissipated progressively over time and distance. The impact forces in rollover are spread over several surfaces of the vehicle. Survival is enhanced if occupants are restrained and not ejected (484,658,659). Occupants can be ejected through side windows (closed or open), the windshield, doors that were originally closed but forced open by the crash, and the sunroof (658). Side window ejections are most common in fatalities. Closed windows can disintegrate secondary to crash forces. A person partly ejected during a rollover can also be injured if trapped between the vehicle and the outside (658).

Head and thoracic injuries are common (657). The former is the result of roof and pillar contact; the latter from interior contacts (Figs. 68 and 69; refs 656 and 657). Although an intruding or buckled roof may cause craniocerebral trauma, most such injuries are caused by ejection (656). Depending on the direction of vehicle rotation, side of initial roof impact with the ground (i.e., side opposite to the direction of rollover), and occupant number, location, kinematics, and seat belt use, head injury results from contact with either the vehicle interior (e.g., roof pillars, roof), vehicle exterior (e.g., roof), or the ground (Fig. 70; refs. 656 and 657). Occupants can be displaced across the vehicle (656). Some victims trapped in their vehicles may succumb from positional asphyxia (see Chapter 3, Subheading 3.7.; Fig. 63; and ref. 660).

Fig. 69. Rollover; restrained driver found dead in vehicle. (A) Triangular right parietotemporal skull fracture documented at autopsy. (B) Corresponding right scalp laceration caused considerable blood spatter on roof interior. Driver had been partially ejected on initial roof impact on the driver's side and was found in her seat (see Fig. 70D). (Reprinted from ref. 656 with permission from the Journal of Forensic Sciences.)

Fig. 69. Rollover; restrained driver found dead in vehicle. (A) Triangular right parietotemporal skull fracture documented at autopsy. (B) Corresponding right scalp laceration caused considerable blood spatter on roof interior. Driver had been partially ejected on initial roof impact on the driver's side and was found in her seat (see Fig. 70D). (Reprinted from ref. 656 with permission from the Journal of Forensic Sciences.)

Fig. 70. Passenger car rollovers; observed rollover events leading to ejection of driver. Estimated speeds >100 km/h (60 mph). (A) Driver, unrestrained and sole occupant. Clockwise rotation, initial impact of rolled car on passenger side, driver ejected through left front window. (B) Driver, unrestrained and sole occupant. Counterclockwise rotation; driver shifted to passenger side. Initial impact on driver's side; driver ejected through right front window. (C) Driver, unrestrained. Right front passenger (with/without restraint). Counterclockwise rotation; driver either ejected completely through left front window early in rollover or partially during initial impact on driver's side. (D) Driver, restrained. Counterclockwise rotation; partial ejection on impacted (driver's) side of vehicle (see Fig. 69). (Reprinted from ref. 656 with permission from the Journal of Forensic Sciences.)

Fig. 70. Passenger car rollovers; observed rollover events leading to ejection of driver. Estimated speeds >100 km/h (60 mph). (A) Driver, unrestrained and sole occupant. Clockwise rotation, initial impact of rolled car on passenger side, driver ejected through left front window. (B) Driver, unrestrained and sole occupant. Counterclockwise rotation; driver shifted to passenger side. Initial impact on driver's side; driver ejected through right front window. (C) Driver, unrestrained. Right front passenger (with/without restraint). Counterclockwise rotation; driver either ejected completely through left front window early in rollover or partially during initial impact on driver's side. (D) Driver, restrained. Counterclockwise rotation; partial ejection on impacted (driver's) side of vehicle (see Fig. 69). (Reprinted from ref. 656 with permission from the Journal of Forensic Sciences.)

Fig. 71. Kinematic trajectories observed in motor vehicle (frontal)-pedestrian collisions. (Reprinted from ref. 656 with permission from the Journal of Forensic Sciences.)

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