Passenger vehicle design has improved over the years enough to counter trends that have decreased safety on the road, according to a new study.

Without these design improvements, the motor vehicle death rate per registered vehicle would have stopped its decline in 1994 and started going up, according to a study by The Insurance Institute for Highway Safety.

“Death rates per vehicle and per mile have been going down for decades, and they still are,” Institute President Adrian Lund said in a statement. “In recent years it’s the vehicles, not better drivers or improved roadways.”

The study revealed the importance of vehicle design changes and the kinds of vehicles motorists are choosing to drive. On the downside, however, is a loss of momentum for effective traffic safety policies on seat belt use, alcohol-impaired driving and speeding, the study asserted.

Researchers separated vehicle effects from other effects on motor vehicle death rates during 1985-2004 by estimating what the death rate trend would have been if vehicle designs hadn’t changed over the years. “In other words, if people still were driving the kinds of vehicles they drove in 1985,” Mr. Lund said.

The death rate trend given this hypothetical vehicle fleet started to go up in the 1990s–very different from the actual downward trend during the past 10 years.

“This suggests that an increasingly dangerous traffic environment has been offset since 1994 only because people are driving vehicles that are more protective,” Mr. Lund said, adding, “Of course the vehicle design changes are good, but people shouldn’t have to buy new, more crashworthy vehicles to maintain their safety.”