A 10-year study examining passenger vehicle fatality rates across all classes of vehicles delivers encouraging news from the National Highway Traffic Safety Administration (NHTSA).

They say that while the number of registered passenger vehicles (passenger cars, light trucks, vans and SUVs) has increased from 204 million in 2000 to 239 million in 2009, the number of fatalities, fortunately, has decreased.

While the number of registered passenger cars increased from 128 million in 2000 to 137 million in 2009, the number of occupant fatalities decreased from 20,699 to 13,095 during the same period and the fatality rate for passenger vehicles has decreased to 9.54 per 100,000 registered vehicles.

When it comes to SUVs, the number of registered vehicles has nearly doubled from 20.7 million SUVs in 2000 to 41.3 million in 2009 and occupant fatalities have increased from 3,358 to 4,091 over the same period. Over the same period, the fatality rate has improved significantly from 16.19 per 100,000 vehicles in 2000 to 9.89 in 2009. However, at 9.89 that's notably more risk than the the 9.54 for all U.S. passenger cars.

As we all know, the reason for the greater chance of fatality is that they are more prone to rollovers. NHTSA says the proportion of fatalities in rollovers was the highest for SUVs (56 percent); followed by pickup trucks (48 percent); vans (33 percent) and passenger cars (25 percent).

SUVs have a higher center of gravity and that is one of the reasons why rollovers occur; drivers turn too fast and the pressure of the weight shift against the wheels on one side becomes a battle the tires often lose.

Obviously rollovers aren't limited just to SUVs, but despite engineering improvements in recent years, they are still at the greatest risk of rollover during a crash. When vehicles with a high center of mass are traveling at high speeds their stability is compromised which means that almost any sort of collision will allow the possibility of a rollover.

NHTSA says 95 percent of single-vehicle rollovers are caused by "tripping" which means that the vehicle slides sideways and disallows the tire to continue in its path. Since most SUVs are not built with roll cages, when a SUV rolls onto its roof the chance of fatality increase due to the higher likelihood of crush injuries especially to the head. These circumstances also hinder escape for passengers and drivers.

Rollovers are the greatest vehicle causes of head injuries and ejections in traffic collisions. Should 'roll cage' protection be mandated for SUVs?