Safety belt use laws in only 21 states and the District of Columbia are primary, meaning police may stop vehicles solely for belt law violations. But in most states belt use law enforcement is secondary, so police cannot stop vehicles for this infraction alone (New Hampshire is the only state without a belt use law). In a new study the Institute found that when states strengthen their laws from secondary enforcement to primary, driver death rates decline by an estimated 7 percent.
"In states with primary laws, belt use rates are higher. The result is that crash deaths are reduced," says Susan Ferguson, Institute senior vice president for research. "Where primary laws are in effect, drivers are more likely to buckle up because the perception is that they're going to be pulled over if they don't."
The most recent national observational survey conducted in 2004 by the National Highway Traffic Safety Administration shows belt use rates averaging 84 percent in primary states compared with 73 percent in secondary states. A number of observational studies have shown that shifting from secondary to primary laws boosts safety belt use, but the Institute's is the first study to evaluate the effect of this shift on traffic deaths.
The Institute examined driver fatality data during 1989-2003 in 10 jurisdictions — California, the District of Columbia, Georgia, Indiana, Louisiana, Maryland, Michigan, New Jersey, Oklahoma, and Washington — where secondary laws were amended to primary. Researchers compared these data with data in states where the laws remained secondary.
The annual rate of passenger vehicle driver deaths per mile of travel declined in both groups of states, but it declined more in the states that changed to primary enforcement. Taking into account the timing of the change in each state and other factors that could have affected crash rates, primary laws were associated with a 7 percent reduction in death rates.
Ferguson points out that during the study period "many states participated in special 'Click It or Ticket' safety belt enforcement campaigns. The enhanced enforcement began earlier in the primary states, so it's important to note that changes in belt use laws along with the increased enforcement led to the decrease in fatalities."
Based on the reduction in driver death rates, it's estimated that 2,990 lives have been saved in the study states because of the tougher safety belt laws.
"If the 28 states that still have secondary laws were to switch to primary enforcement, about 700 lives would be saved each year. And if legislators in these states had enacted primary laws to begin with, more than 5,000 lives could have been saved since 1996," Ferguson says.
Effects of strengthening belt laws
Lives that could have been saved since 1996 in secondary states if belt laws had been primary
||Passenger vehicle driver deaths 1996-2003
||Lives that could have been saved since 1996