Depending on the level of high-visibility enforcement that they employ, however, far greater results are possible. 2-13) Recent research (Masten, 2007) has provided strong support that changing from secondary to primary enforcement [of] seat belt laws increases occupant seat belt use during the nighttime hours as well as the daytime hours when most observational surveys of seat belt use are conducted. 2-13) [Hedlund, Gilbert, et al., 2008] studied the effects of primary law changes on seat belt use and occupant fatalities in Michigan, New Jersey, Washington, Delaware, Illinois, and Tennessee.
Strong evidence was found in the FARS data for all 6 States that primary seat belt laws increase seat belt use.
Rates of seat belt use are 9 percentage points higher in primary enforcement states than secondary states.
If the overall prevalence of seat belt use in states with secondary enforcement laws had matched the higher prevalence in states with primary laws, an additional 7.3 million adults would have buckled up in 2008.
Studies of 5 States that changed their belt use laws from secondary to primary enforcement found that belt use increased from 12 to 18 percentage points where all passenger vehicles were covered by the law and 8 percentage points in one State where pickup trucks were excluded (Nichols, 2002).