Although many factors contribute to passenger injury during a vehicle crash, the kinetic energy transferred to the occupants is the causal agent of injury, Friedman said.
"Speed kills. When travel speeds increase, the energy transferred to the occupants of a vehicle during a crash increases, which increases the risk and severity of injury," he said. "Researchers have demonstrated that lower travel speeds and death tolls usually follow lowering of speed limits, and higher travel speeds and death tolls follow increases in speed limits," he added.
But not everyone agrees that lowering speed limits is a viable solution. "Driving fast can prove fatal, but most of the time gets us from A to B more efficiently," said Dr. David L. Katz, director of the Prevention Research Center at Yale University School of Medicine in New Haven, Conn. "Driving slow will save the lives of some, but gum up the schedules of all," he said.
A pragmatic response to the data presented in this study must consider both concerns, Katz said.
"I hope for a 21st-century solution: adjusting speed limits based on traffic, weather conditions and terrain; cars and roadways better engineered for safety at higher speeds; alternative energy vehicles that solve the emission problem by means other than reduced speed and enhanced driver training," he said.
Dr. Stephen Olvey, an associate professor in the department of neurological surgery at University of Miami Miller School of Medicine in Florida, said that with airbags and seat belts, cars are safer today, so 55 might be too slow.
"In the study, states that kept the speed limit at 65 showed a decline in fatalities, and it was the states that went up above that that had significant increases," said Olvey, who has been a medical advisor to a professional race car team.
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