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.
Types of tripped rollovers:
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.
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.
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.