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Rollover- Causes and Types

Author / Coordinator:  
March 2007

Rollovers are complex crash incidents and are particularly violent in nature. Rollovers, more so than other types of crashes, reflect the interaction of the driver, road, vehicle, and environmental factors. So while vehicle type does play a significant role, other factors such as driver behavior and road and environmental conditions can also cause a vehicle to roll over.
All types of vehicles can rollover. However, taller, narrower vehicles such as SUVs, pickups, and vans have higher centers of gravity, and thus are more susceptible to rollover if involved in a single-vehicle crash.
Fatal rollover crashes are speed-related more often than fatal non-rollover crashes. Some 40% of fatal rollover crashes involved excessive speeding. Additionally, nearly ¾ of fatal rollovers took place where the posted speed limit was 55 miles per hour or higher.
Nearly half of all fatal rollover crashes involve alcohol. Impairment can result from any blood alcohol concentration (BAC) above .00. Even a small amount of alcohol will negatively affect your judgment, muscular coordination, and vision, making you more likely to lose control of your vehicle.
Rural roads tend to be undivided and without barriers. They are thus more likely to be the scene of a fatal rollover. Almost ¾ of fatal rollovers occur in rural areas where the posted speed limit is typically 55 miles per hour or higher.
NHTSA data also suggest that over 90% of the vehicles in fatal, single-vehicle rollover crashes were involved in routine driving maneuvers (going straight or negotiating a curve) at the time of the crash. This further suggests that driver behavior (distraction, inattentiveness, speeding, and impaired driving) plays a significant role in rollover crashes.
NHTSA data show that nearly 85% of all rollover-related fatalities are the result of single-vehicle crashes. This means that the majority of rollover crashes and fatalities do not involve any other vehicle besides the one that rolled over, further suggesting that driver behavior plays a significant role in rollover crashes.

Rollover: Types

Rollovers occur in one of two ways: tripped or un-tripped.
NHTSA data show that 95% of single-vehicle rollovers are tripped. This happens when a vehicle leaves the roadway and slides sideways, digging its tires into soft soil or striking an object such as a curb or guardrail. The high tripping force applied to the tires in these situations can cause the vehicle to roll over.
One of the best ways to avoid a rollover, therefore, is to stay on the road. Electronic Stability Control is a promising new technology that will help drivers stay on the road in emergency situations.

  • Curbs, soft soil/shoulders, guardrails, pavement surface discontinuities, snow banks, or other objects can cause tripping.
  • Tripping can also occur when a vehicle is traveling forward, typically at a high speed. If one side of the vehicle rides up on an object, like a guardrail, it may be forced to roll over.
  • Tripping can also occur on severe slopes in off-road situations. If an incline’s slope is too steep to keep the vehicle upright, it can topple over.

    Un-tripped rollovers are less common than tripped rollovers, occurring less than 5% of the time, and mostly to top-heavy vehicles. Instead of an object serving as a tripping mechanism, un-tripped rollovers usually occur during high-speed collision avoidance maneuvers.  Un-tripped rollovers do not occur on slippery roads. They are the result of normal surface friction.