Deaths, Injuries Increase With Higher Speed Limits

THURSDAY July 16, 2009 -- Deaths and injuries on America's interstates have increased since the repeal of the federal 55-mile-per-hour speed limit in 1995, a new study finds, and some believe it's time to slow down again.

Researchers tracking fatalities attributed 12,545 deaths and 36,582 injuries in fatal crashes to higher speed limits implemented during the 1995-2005 study period.

"Our study clearly shows that policy can directly result in more deaths as well as reducing deaths on our country's roads," said lead researcher Lee S. Friedman of the division of environmental and occupational health sciences in the School of Public Health at the University of Illinois, Chicago.

Their results show that seemingly harmless policy decisions can have long-term repercussions, the researchers said. They called for implementation of a national speed management policy that would include a maximum speed of 55 mph and development of camera networks to curb speeding.

The report is published in the July 16 online edition of the American Journal of Public Health.

For the study, Friedman's group examined deaths and injuries in fatal car crashes on rural interstate highways, urban interstates and non-interstate roads.

They found a 3.2 percent increase in deaths because of higher speed limits on all types of roads in the United States. The largest increase -- 9.1 percent -- was on rural interstates, followed by urban interstates at 4 percent. "These roads were the main locus of raised speed limits," they noted.

Some states had imposed a 65 mph limit. Others went to 70, and still others, 75. The solution, said Friedman, is to bring back the 55 mph speed limit.

"Reduced speed limits would save lives," Friedman said. "They would also reduce gas consumption, cut emissions of air pollutants, save valuable years of productivity and reduce the societal cost of motor vehicle crashes," he added.

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.

Cars and roads have been updated and improved, Olvey said. "Rather than 55 mph, you could have the same effect now at 65 mph," he said. "If you allow 70 and 75 mph, then you are going to have the increase in loss of life and expense."

More information

For more information on highway deaths, visit the U.S. National Highway Traffic Safety Administration .

Posted: July 2009


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