The institute’s study shows the designs of passenger vehicles have been improving for years, becoming more protective of their occupants in crashes. Without these improvements, researchers say the motor vehicle death rate per registered vehicle would have stopped declining in 1994 and started going up, officials said.

Death rates per vehicle and per mile have been going down for decades, and they still are, said IIHS President Adrian Lund. "The study reveals not only the importance of the vehicle design changes and the kinds of vehicles motorists are choosing to drive, but, on the downside, the loss of momentum for effective traffic safety policies on belt use, alcohol-impaired driving and speeding.

Of course the vehicle design changes are good, said Lund, but people shouldn’t have to buy new, more crashworthy vehicles to maintain their safety.

The entire research report will be published later this year in the journal Traffic Injury Prevention.