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Effectiveness: 5 Star Cost: $
Use: Medium
Time: Short

Primary enforcement seat belt use laws permit law enforcement officers to stop and cite a violator independent of any other traffic violation. Secondary enforcement laws allow law enforcement officers to cite violators only after they first have been stopped for some other traffic violation.


As of August 2020 there were 34 States and the District of Columbia that had primary belt use laws, 15 States had secondary enforcement laws, and New Hampshire had no belt use law applicable to adults (GHSA, 2020). However, some States only have primary enforcement for certain occupants (for instance drivers or people older than a specified age) and secondary enforcement for other occupants (for example, North Carolina’s seat belt law is primary for drivers and front-seat passengers 16 and older, but secondary for rear-seat passengers 16 and older). Twenty States do not have laws requiring the use of seat belts in the rear seat (GHSA, 2020). Most State seat belt use laws cover passengers over a specified age and are designed to work in combination with CPS laws covering younger passengers.

Additionally, in some States with secondary enforcement belt use laws, individual communities have enacted and enforced community-wide primary laws or ordinances. These laws differ from statewide laws only in that they are enacted, publicized, and enforced locally. No comprehensive data are available on how many communities have primary laws, but local implementations have occurred in States such as Missouri (Missouri Department of Transportation, 2017).


Early research found that primary enforcement laws were associated with increased seat belt use ranging from 6% to nearly 20% (Hedlund et al., 2008; Nichols, Tippetts, et al., 2010; Nichols et al., 2014; Shults et al., 2004) and a 2% to 10% reduction in occupant fatalities (Farmer & Williams, 2005; Hedlund et al., 2008; Shults et al., 2004). Seat belt increases were found across a diverse range of drivers and passengers (Nichols et al., 2012; Shults et al., 2004), both at night and during the day (Chaudhary et al., 2010; Masten, 2007).

However, more recent studies suggest the safety benefits of upgrading to a primary law from a secondary law may not be as great as when seat belt use was lower overall (Harper & Strumpf, 2017; Harper, 2019). In 2004 seat belt use in primary-law States was over 10 percentage points higher than use in secondary-law States (84% versus 73%) (Glassbrenner, 2004). Today the difference is much less significant. In 2022 seat belt use in primary-law States was nearly 3 percentage points higher than use in secondary-law States (92.2% versus 89.5%) (NCSA, 2023a). High overall seat belt rates and improvements in road and vehicle safety (front and side air bags, electronic stability control, advanced driver assistance systems) have contributed to a decrease in crash fatalities (Farmer & Lund, 2015). While recent studies do still suggest that changing a seat belt law from secondary to primary enforcement has benefits, States may not experience the large impacts seen in earlier studies.

Additionally, research suggests that primary seat belt laws may be less effective in regions with certain economic, societal, and cultural characteristics. Specifically, there is initial evidence that primary seat belt laws were only associated with higher belt use rates in States that had higher levels of academic achievement and higher health rankings (Ash et al., 2014). Moreover, primary-law States that had a high proportion of rural roads relative to urban roads were associated with no significant increase in seat belt usage in comparison to States with secondary seat belt laws.

A further consideration is whether the primary seat belt law covers all seating positions. The NOPUS has typically found higher observed rear-seat belt use in States with belt laws covering all seating positions than in States not requiring rear-seat belt use, though for the first time since 2005 the opposite was true in 2021 (77.7% and 78.8%, respectively) (Boyle, 2022). An analysis of Iowa, which has primary laws for front-seat passengers but no law for rear-seat passengers, found that occupants reported using seat belts 30%-40% less often if they were a passenger in the rear than in the front (McGehee et al., 2014). This is consistent with findings obtained using national household survey data from the ConsumerStyles 2012 database (Bhat et al., 2015).

Specifically looking at the impact of primary enforcement on rear-seat fatalities, Findley et al. (2018) examined rear-seat fatalities to determine the impact of changing from secondary to primary enforcement. From 2011 to 2015 a total of 3,061 unrestrained rear-seat passengers were killed in secondary-law States. Findley et al., determined that between 772 to 1,990 of the fatalities in secondary-law States could have been prevented by the increased restraint use associated with primary-law States.

A good seat belt use law should be comprehensive, covering all seating positions equipped with a seat belt in all passenger vehicles (ACTS, 2001; NCUTLO, 2000; NHTSA, 2003). Such a law sends a clear and consistent message to the public. However, it is also important to consider how the law is enforced once implemented. Primary seat belt use laws have raised equity concerns. See the introduction for more information and discussion related to equity and enforcement practices.


Once legislation has been enacted to upgrade a secondary law to primary, the costs are for publicity and enforcement. Publicity costs may be low if the media covers the law change extensively. Law enforcement can adapt its secondary law enforcement strategies for use under the primary law or may be able to use new strategies permitted by the primary law. States wishing to increase enforcement and publicity to magnify the effect of the law change will incur additional costs.

Time to implement:

A primary seat belt use law can be implemented as soon as the law is enacted unless it has a delayed effective date or includes a warning period before enforcement is authorized.