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

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

Use: As of June 2019 there were 34 States and the District of Columbia that had primary belt use laws and 15 States had secondary enforcement laws. Only New Hampshire had no belt use law applicable to adults (GHSA, 2019a; IIHS, 2019a). 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, 2019a). More information on the effect of having no rear seat belt requirement is included in the “Other Issues” section below.

Effectiveness: In 2019 belt use averaged 92.0% in the 34 States and District of Columbia with primary belt laws and 86.2% in States with secondary or no enforcement laws (NCSA, 2019). Nichols, Tippetts, et al. (2010) examined the relationship between the type of seat belt law enforcement and seat belt use from 1997 to 2008. Compared with secondary laws, primary laws were associated with a higher observed seat belt use (10 to 12% higher) and higher seat belt use among front-seat occupants killed in crashes (9% higher).

The CDC’s systematic review of 13 high-quality studies (Shults et al., 2004) found that primary laws increase belt use by about 14 percentage points and reduce occupant fatalities by about 8% compared to secondary laws. Similarly, Nichols et al. (2014) found that primary enforcement laws were associated with a 9- to 10-percentage-point increase in belt use. In another study, Farmer and Williams (2005), found that passenger vehicle driver death rates dropped by 7% when States changed from secondary to primary enforcement. However, the findings from a recent analysis of crash fatalities suggest that the safety benefits of upgrading to a primary law from a secondary law may not be as great as in earlier periods when seat belt use was lower and implementing primary laws resulted in more reductions in crash fatalities specifically associated with increased seat belt use (Harper & Strumpf, 2017). One possible explanation is that recent improvements in road and vehicle safety, in addition to the reduction in VMT post 2008, have reduced the proportion of fatal crashes that could benefit from increased belt use. It should be noted that the analysis did not account for before-and-after belt use rates in the States, which also may have contributed to the smaller observed benefits.

Research has provided strong support that changing from secondary to primary enforcement seat belt laws increases occupant seat belt use during the nighttime hours as well as the daytime hours (Chaudhary et al., 2010; Masten, 2007). Chaudhary et al. (2010) evaluated the effects of Maine's change from secondary to primary enforcement of their seat belt law. Observational surveys conducted over an 18-month period after this change went into effect measured increases in seat belt use from 77% to 84% during the daytime and from 69% to 81% at night.

Hedlund 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 that primary seat belt laws increase seat belt use. Furthermore, statistically significant decreases in the number of front-seat passenger vehicle occupant fatalities were found in Michigan and Washington and the decrease in New Jersey was marginally significant. The lack of significant effects on fatalities in Illinois and Tennessee, as well as a marginal increase in Delaware, was attributed in part to the short amount of time since the implementation of the primary provisions in these States as well as the small number of fatalities in Delaware.

Costs: Once legislation has been enacted to upgrade a secondary law to primary, the costs are to publicize the change and enforce the new law. Publicity costs to inform the public of the law change 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 (see the Seat Belts and Child Restraints Chapter, Section 2.1).

Time to implement: A primary belt use law can be implemented as soon as the law is enacted unless it has a delayed effective date, however it could include a warning period before enforcement is authorized.

Other issues:

  • Partial coverage seat belt laws: Most State belt use laws cover passengers over a specified age and are designed to work in combination with child passenger safety laws covering younger passengers. However, belt use laws do not cover adult rear seat passengers in 20 States (GHSA, 2019a). The National Occupant Protection Use Survey (NOPUS) 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 (84.3% and 62.7% in 2017, respectively) (Li & Pickrell, 2019). 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 to 40% less often if they were a passenger in the rear than in the front (Reyes et al., 2014). This is consistent with findings obtained using household survey data from the ConsumerStyles 2012 database (Bhat, Beck, Bergen, & Kresnow, 2015). Most States’ laws exempt some vehicles, such as those designed for more than 10 passengers, taxis, emergency vehicles, postal delivery vehicles, farm vehicles, pickup trucks, or vehicles not required to have seat belts (Glassbrenner, 2005). Some States exempt passengers for specified medical or physical reason. 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.
  • Opposition to primary seat belt laws: Opponents of primary seat belt use laws claim that primary laws impinge on individual rights and provide opportunities for law enforcement to harass minority groups (St. Louis et al., 2011). Studies in several States have found that minority groups were ticketed at similar or lower rates than others after a primary law was implemented (Shults et al., 2004; Tison et al., 2011). When Michigan changed from a secondary to a primary law, harassment complaints were very uncommon both before and after the law change. The proportion of seat belt use citations issued to minority groups decreased under the primary law (Eby et al., 2004). In a telephone survey, the vast majority of people who actually received seat belt citations did not feel that they were singled out on the basis of race, age, or gender. However, some minorities and young drivers reported perceptions of harassment.
  • Effect on low-seat-belt-use groups: Studies in States that changed their laws from secondary to primary show that belt use increased across a broad range of drivers and passengers. In some States, belt use increased more for low-belt-use groups, including Hispanics, African Americans, and impaired drivers, than for all occupants (Shults et al., 2004). This was also found in Florida where the greatest gains were among males, African Americans, pickup truck occupants, younger occupants, and those on local roads (Nichols et al., 2012).
  • Impact of regional characteristics on effectiveness of primary seat belt laws: 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 also associated with no significant increase in seat belt usage in comparison to States with secondary seat belt laws.