Leflaw.com

The failure of the roof of a car or truck is the most likely failure to cause death or permanent injury and the roof is, without doubt, the least crashworthy part of a vehicle. In fact, roofs are so soft that when test dropped upside-down a mere 12 inches the result is total crush that can cause death, permanent brain and spinal cord injuries.

Most rollovers occur due to tipping. SUVs, because of vehicle instability, will "tip" when a mild turning movement in one direction is followed by a quick correction in the opposite direction. The roll that follows causes the vehicle to be tossed and to land on its roof on the side opposite the roll. That is why SUV drivers and passengers are twice as likely to be killed in a rollover than those in a standard vehicle.