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Posted 01.17.06

'Primary Enforcement Laws' Increase Seat Belt Use, MU Researcher Finds

COLUMBIA, Mo. -- Seat belt usage among Missouri motorists could rise to more than 90 percent, saving the state millions of dollars, if a simple change were made in seat belt law enforcement, according to research conducted at the University of Missouri-Columbia. The current rate of seat belt use among Missourians is 76 percent. In 2002, Missouri ranked 35th in the nation in belt use rate, with a fatality rate of 21.6 people per 100,000 people. The national average is 14.6, and the safest state has a rate of 7.2.

Today in the U.S., 49 states have mandatory seat belt laws. Of those, 22 states, including the District of Columbia, have primary enforcement laws, which allow a police officer to stop a motorist specifically for not wearing a seat belt. Currently, Missouri has a secondary enforcement law, which means an officer cannot stop a motorist solely because the motorist isn't using a seat belt.

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"Because primary enforcement increases the chances of receiving a citation for failure to obey the law, such laws enhance seat belt use," said Lilliard Richardson, associate professor in MU's Truman School of Public Affairs. "Research shows states that switched from secondary to primary enforcement between 1993 and 2003 experienced a 20 percent increase in seat belt use. Even after controlling for other factors, statistical analysis showed seat belt use in primary enforcement states was 9.1 percentage points higher compared to secondary enforcement states."

Richardson predicts that if Missouri becomes a primary enforcement state, fatalities could decrease by 5.9 percent and injuries by 4.9 percent, or about 3,400 per year. Estimates of traffic injury costs by the National Highway Traffic Safety Administration show the reduction in injuries and fatalities under a primary enforcement law could save Missourians up to $133 million per year in medical, legal, rehabilitation and workplace costs.

The amount of the fines drivers receive for not using seat belts also affects seat belt use. Missouri requires only a $10 fine for failure to wear a seat belt. According to Richardson, Missouri could increase belt use by an additional 4 percentage points by increasing the fine to $25 and by 8 percentage points with an increase to a $50 fine. Combined with a primary enforcement law, a $50 fine would increase Missouri's belt use rate to more than 90 percent.

"Comparison of traffic fatality rates in the Midwest shows a direct correlation between seat belt use and number of fatalities," Richardson said. "States with high seat belt use, most with primary enforcement, had lower fatality rates compared to states with low seat belt use, which were those with secondary enforcement. For example, seat belt usage in Illinois increased from 74% in 2002 to 83% in 2004 after a switch to primary enforcement.

Richardson's research was published in the November 2005 issue of Accident Analysis and Prevention.



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