Public Release: 

'Upgrading' from secondary to primary seatbelt laws would save lives, researchers find

University of Missouri-Columbia

COLUMBIA, Mo. - Vehicle crashes claim approximately 42,000 lives each year, according to statistics from the U.S. Department of Transportation. Recently, Missouri and other states have been considering a law that would encourage seatbelt use. Research conducted by a University of Missouri-Columbia professor sheds new light on the importance of seatbelts and laws that encourage their use.

Lilliard Richardson, associate professor in MU's Truman School of Public Affairs, and David J. Houston, associate professor at the University of Tennessee, Knoxville, conducted two studies of primary seatbelt enforcement, and both demonstrate the effectiveness of such laws in saving lives. Primary enforcement laws allow law enforcement officers to pull over drivers and ticket them if they are not wearing their seatbelts. Secondary enforcement laws, on the other hand, only allow an officer to pull over drivers for a separate violation (speeding, headlight out, etc.) and then ticket them if they are not wearing their seatbelts. Twenty-four states have primary enforcement laws, whereas others, including Missouri, only have secondary enforcement laws. New Hampshire has no seatbelt law. A bill to change enforcement from secondary to primary recently passed in the Missouri House and Senate.

In the study "Safety Belt Use and the Switch to Primary Enforcement," Richardson and Houston developed statistical models of observed seatbelt use in 47 states and the District of Columbia from 1991 to 2003. They found that states could increase belt use by 10 percent and improve public safety considerably by upgrading to primary enforcement.

"Seatbelts save lives, and stronger seatbelt laws increase seatbelt use," Richardson said. "Many studies have examined the effects of primary and secondary enforcement laws, but our study is one of only a few to look at the gains that can be made by upgrading from a secondary to a primary law. Our results show that seatbelt use increased when states upgraded to primary enforcement laws, and this means that upgrading can save lives."

Thirteen of the 47 states studied changed their laws from secondary to primary between 1991 and 2003. Richardson and Houston found that seatbelt use in all of the states studied increased during the 13-year study, but states with primary enforcement laws consistently had the highest use of seatbelts, and states with only secondary enforcement laws had the lowest usage rates. States that started the study with secondary enforcement laws and then upgraded to primary enforcement laws experienced the greatest average increase in belt use. States that had primary enforcement laws throughout the study saw seatbelt use increase from 68.4 to 86.1 percent, whereas states that upgraded saw an increase from 55.5 to 82.7 percent.

Another study done by Richardson and Houston, "Reducing Traffic Fatalities in American States by Upgrading Seat Belt Use Laws to Primary Enforcement," showed a strong link not just between primary enforcement laws and seatbelt use, but between primary enforcement laws and a reduction in fatalities. The study found that fatality rates in states with secondary enforcement laws remained stable between 1990 and 2002, whereas fatality rates in states with primary enforcement laws continued to steadily decline. Even with statistical controls for demographic changes in the states over time, primary enforcement states showed nearly double the reduction in fatalities compared to secondary states. Further, an upgrade to primary enforcement was associated with a 5.1 percent decline in fatalities for drivers and a 4.7 percent decrease in all vehicle occupant fatalities. The study estimated that the ten states and District of Columbia that upgraded from secondary to primary enforcement laws saved 3,553 lives between 1993 and 2002.

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"Safety Belt Use and the Switch to Primary Enforcement" was published in the American Journal of Public Health in November 2006, and "Reducing Traffic Fatalities in the American states by Upgrading Seatbelt Use Laws to Primary Enforcement" was published in the Journal of Public Analysis and Management in June 2006.

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