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Motor Vehicle Injury – Safety Belts: Primary (vs. Secondary) Enforcement Laws


What the Task Force Found

About The Systematic Review

The Task Force finding is based on evidence from a systematic review of 13 studies (search period through June 2000). The review was conducted on behalf of the Task Force by scientists from CDC’s Division of Unintentional Injury Prevention with input from a team of specialists in systematic review methods and experts in research, practice and policy related to motor vehicle injury prevention.


As of February 2015, 49 states, the District of Columbia, American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, and the Virgin Islands have primary or secondary safety belt laws. Current figures are available from the Governors Highway Safety Administration External Web Site Icon.

Summary of Results

Thirteen studies qualified for the systematic review.

  • Nine studies compared states with primary laws to those with secondary laws.
  • Four studies evaluated the effect of changing from secondary to primary laws.
  • Fatal injuries: median decrease of 8% in primary law states versus secondary law states (interquartile intervals: 3%-14% decrease; 5 studies)
  • Observed seat belt use: median increase of 14 percentage points in primary law states versus secondary law states (interquartile intervals: 12 to 23 percentage points; 5 studies)
  • Police-reported safety belt use: the effect estimate could not be calculated (1 study)
  • Self-reported safety belt use: the effect estimate could not be calculated (2 studies)

Summary of Economic Evidence

An economic review of this intervention did not find any relevant studies.


These findings should be applicable to all U.S. drivers and passengers.

Evidence Gaps

Each Community Preventive Services Task Force (Task Force) review identifies critical evidence gaps—areas where information is lacking. Evidence gaps can exist whether or not a recommendation is made. In cases when the Task Force finds insufficient evidence to determine whether an intervention strategy works, evidence gaps encourage researchers and program evaluators to conduct more effectiveness studies. When the Task Force recommends an intervention, evidence gaps highlight missing information that would help users determine if the intervention could meet their particular needs. For example, evidence may be needed to determine where the intervention will work, with which populations, how much it will cost to implement, whether it will provide adequate return on investment, or how users should structure or deliver the intervention to ensure effectiveness. Finally, evidence may be missing for outcomes different from those on which the Task Force recommendation is based.

Identified Evidence Gaps

  • What are the age, gender, and racial differences between violators in primary and secondary law states?
  • Are primary enforcement laws more or less effective in certain populations?

The following outlines evidence gaps for reviews of these interventions to increase use of safety belts: Laws Mandating Use; Primary (vs. Secondary) Enforcement Laws; Enhanced Enforcement Programs.


All three interventions appear to be effective in most populations and settings. Although some differences in effectiveness for subgroups have been identified in these reviews, other questions regarding differential effectiveness of these interventions remain.

  • What penalties for violations of laws (e.g., fines, license demerits) are most effective among high-risk drivers (e.g., teenagers, drinking drivers)?
  • What are the most effective methods of publicizing enhanced enforcement to reach high-risk drivers?

Other Positive or Negative Effects

Research on the positive and negative effects of each intervention might include:

  • Do primary safety belt laws increase or decrease risky driving?
  • Do enhanced enforcement programs for safety belt use decrease risky driving?
  • Do primary laws or enhanced enforcement programs deter alcohol-impaired driving?
  • Are primary laws associated with changes in frequency of traffic stops for ethnic and racial minorities relative to the general population?

Economic Evaluations

Little economic evaluation information was available. Research is warranted to answer the basic economic questions:

  • What are the cost-benefit, cost utility, and cost-effectiveness of interventions to increase safety belt use?


A number of barriers impede effective implementation of each intervention reviewed. Research into the following areas may help to overcome these barriers.

  • How can communities increase public acceptance of primary safety belt laws?
  • Do enhanced enforcement programs divert police from other crimes?

Study Characteristics

  • All of the included studies compared the effects of primary laws with those of secondary laws in the United States.
    • Studies compared states with primary laws to those with secondary laws (9 studies), or evaluated the effect of changing from a secondary to a primary law (4 studies). There were no studies of states changing from a primary law to a secondary law.
  • Studies were conducted in 49 states and the District of Columbia and looked at drivers and passengers of all ages.
  • Reported outcomes included fatal injuries, observed safety belt use, police-reported safety belt use, and self-reported safety belt use.


Zaza S, Sleet DA, Elder RW, Shults RA, Dellinger A, Thompson RS. Response to letter to the editor. American Journal of Preventive Medicine. 2002;22:330-1.

Sleet DA. Evidence based injury prevention: guidance for community action. In: Australian Third National Conference on Injury Prevention and Control. Australian Third National Conference on Injury Prevention and Control. Brisbane, Queensland, Australia; 1999.