ANN ARBOR—If history is any indication, then the new standard enforcement safety belt law that takes effect in Michigan this March should have a significant impact on getting motorists to buckle up, say University of Michigan researchers.
In their new study to be published in the journal Accident Analysis & Prevention, researchers David W. Eby, Lisa J. Molnar and Michelle L. Olk of the U-M
They found that the use of seat belts in the state increased dramatically immediately after Michigan passed a secondary enforcement law in 1985—from less than 20 percent of drivers and front-seat passengers to more than 60 percent. Although the rate declined to about 45 percent the following year, safety belt rates have steadily risen, especially since the early 1990s.
"The decline leveled off at a rate more than 20 percentage points higher than before the law, indicating the effectiveness of the law in Michigan," Eby says. "Examining this 'bump' in safety belt use across all trends reveals that the law influenced belt use in a general way."
Eby and colleagues say that states with standard enforcement laws (which allow police to stop motorists solely for not using a safety belt) have generally been shown to be more effective in increasing belt use and reducing crash fatalities than states with secondary laws (which allow police to issue belt citations only after they have stopped motorists for another infraction).
In their most recent (1999) annual seat belt survey—the last prior to implementation of the new law—Eby and researchers Jonathon M. Vivoda and Tiffani A. Fordyce found that 70 percent of drivers and front-seat passengers in cars, sport-utility vehicles, vans/minivans and pickup trucks buckle up (more than 9,400 motorists in Michigan's 28 most populous counties were observed).
Although this overall rate remained about the same as that of the previous year, the belt use rate of young adults (ages 16-29) unexpectedly dropped from nearly 64 percent to about 57 percent—due mostly to the failure of many young men to wear safety belts (less than half were found to use seat belts).
While safety belt use, overall, is on the rise nationally, the researchers say that states will have to redouble their efforts to meet this year's national goal of 85 percent belt use and a rate of 90 percent for 2005.
"In developing effective strategies for increasing belt use, it may be instructive for states to carefully examine past trends in belt use and try to identify factors that have exerted an upward influence on those trends," Eby says.
In their study covering the years 1984 to 1998, Eby, Molnar and Olk reviewed data from 20 UMTRI statewide surveys of safety belt use. Their findings show that seat belt use rates have consistently been higher for drivers than for front-seat passengers, for females than for males, and for older drivers than for younger drivers.
While it is unknown why drivers are more apt to wear safety belts than their passengers, the researchers say that the other findings
Once again, these trends were borne out by Eby's 1999 safety belt survey in which 78 percent of women were found to buckle up, compared with 63 percent of men. Likewise, the results show that more than 70 percent of motorists (males and females combined) among all age groups wear seat belts, with the exception of 16-to-29-year-olds.
"Examination of belt use trends in Michigan provides useful information not only for continued efforts to increase belt use in our state, but in all states interested in meeting national goals for safety belt use for this year and beyond," Eby says. "Michigan's experience since 1984 clearly shows that implementation of a belt law can exert a significant upward influence on belt use, with post-law levels remaining well above pre-law levels over the long term."
David W. EbyTransportation Research Institute