Rollover accidents are directly related to a vehicle's stability in turns. The SUV's stability is directly linked to the tie between the center of gravity and the track width (distance between the left and right wheels). A high center of gravity and narrow track can make a vehicle unstable in fast turns or sharp changes of direction--increasing the odds that it will rollover once it begins to skid out of control. The problem is most significant in 4-wheel-drive pickup trucks and sport-utility vehicles, which have a higher ground clearance for off-road driving.
While many vehicles have safe ratios, (or vehicles' stability number) the addition of passengers, cargo and a full tank of gas all occur above the center of gravity, increasing the chance of a rollover accident. In a real world scenario, the SUV would probably have cargo or multiple passengers. The extra weight lowers the ratio to hazardous levels if accidents were to occur at regular highway speeds.
SUV rollovers are nearly three times more likely to occur than the average passenger car, and government tests indicate the most stable SUV is still more unstable than the most unstable car.