NEW YORK (CNN/Money) - Bigger cars really are safer. That's the conclusion of a new study from the National Highway Traffic Safety Administration.

Occupants of lighter vans, pickup trucks and SUVs were more likely to die in crashes, according to the study. NHTSA analyzed crash data from 1995 to 2000 involving 1991 to 1999 model vehicles. Researchers attempted to statistically adjust for the age and gender of drivers and other variables such types of roads.

NHTSA researchers found that four-door passenger cars and minivans had the lowest fatality rates of all vehicle types. Small four-door cars, mid-sized SUVs and compact pickup trucks had the highest death rates.

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Mid-sized SUVs are nine times as likely to be involved in fatal roll-over accidents and are also twice as likely to kill occupants in other vehicles, NHTSA said. In non-rollover crashes, SUVs are about as safe as other vehicles of similar weight, according to the study.

Among passenger cars and the lightest light trucks and vans, even a one-hundred pound lower weight significantly increased the risk of death. Modest weight differences in the heaviest light trucks and vans, however, did not change the risk of death for occupants of those vehicles. Among those heavyweight vehicles, however, slighly lighter ones were associated with fewer deaths in vehicles they hit.