A rollover is a crash in which the vehicle revolves at least one-quarter turn (which would be onto its side), regardless of whether the vehicle ends up laying on its side, roof, or even returning upright on all four wheels. Rollovers occur in multiple ways, Most rollovers are “tripped,” that is, the vehicle rolls over after leaving the roadway and striking a curb, soft shoulder, guardrail, or other object that “trips” it. A small percentage of rollover events are “untripped,” (e.g., the result of a tire and/or interface friction).

Rollover crashes are rare but deadly. Vehicles roll over in only 2% of the nearly 9.1 million passenger car, SUV, pickup and van crashes. Yet these crashes account for more than a third of all passenger vehicle occupant deaths. In 2010 alone, more than 7,600 people died in rollover crashes, the majority of whom (69%) were not wearing safety belts.  The annual cost of rollover injuries and fatalities is approximately $50 billion.

Handling instability refers to how the vehicle stays in contact with the road and remains in the travel lane during ordinary driving maneuvers. Good handling and yaw stability (the vehicle’s ability to stay pointed in the direction the driver intended) can reduce the number of “loss of control” crashes that often lead to rollover by assisting the driver in maintaining control of the vehicle.

Electronic Stability Control (ESC) is a technology design to assist drivers in maintaining control of their vehicles during extreme steering maneuvers. ESC helps prevent sideways skidding and loss of control that can lead to rollovers by sensing when the vehicle is starting to spin out (over-steer) or plow out (under-steer) and helping to turn the vehicle to the appropriate heading by automatically applying the brake at one or more wheels (ESC takes over the brakes and may affect the throttle, but not the steering).

Slowing the vehicle not only directly reduces the likelihood of a rollover, but also improves the controllability of the vehicle, thereby reducing the likelihood of having a single-vehicle crash in the first place.

ESC reduces the risk of fatal single-vehicle rollovers by more than 70 percent and is estimated to cost less than $300 per vehicle. Yet manufacturers originally only included ESC on their higher-end vehicles or as an upgraded option for American consumers (the same manufacturers made ESC a standard feature for vehicles sold in Europe). “It’s not rocket science,” notes Lee Brown, “It’s science that was put into production in 1998 because it dramatically works. With this technology, the vehicle can help you safely drive.” Nevertheless, it wasn’t until the model year 2012 that all passenger cars included the technology.

Even with standard ESC on all new vehicles, rollovers still occur, so having a strong roof remains important.


David Pittle, Sr., VP, Consumer Union:
"These systems should be standard equipment in all SUVs. Their widespread use is virtually certain to result in fewer rollover-related deaths and injuries."

Don Sherman, Popular Mechanics:
"It's like having God as your co-pilot."

Dr. Hans-Joachin Schaps, Head of Passenger Car Development, Mercedes Benz:
"ESC makes an important contribution to accident prevention, and is therefore as significant for traffic system as ABS, seat belts and airbags."

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