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


What the CPSTF Found

About The Systematic Review

The CPSTF 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 CPSTF 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 June 2017, 34 states, the District of Columbia, American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, and the Virgin Islands have primary safety belt laws for front seat occupants, and 15 states have secondary safety belt laws for front seat occupants. Current figures are available from the Governors Highway Safety Administration External Web Site Icon.

Summary of Results

More details about study results are available in the published evidence review pdf icon [PDF - 2.85 MB].

The systematic review included 13 studies.

  • Nine studies compared states with primary laws to states with secondary laws.
  • Four studies evaluated the effect of changing from secondary to primary laws.
  • Fatal injuries decreased by a median of 8% in primary law states versus secondary law states (5 studies).
  • Observed seat belt use increased by a median of 14 percentage points in primary law states versus secondary law states (5 studies).
  • Police-reported safety belt use could not be calculated (1 study).
  • Self-reported safety belt use 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

CPSTF identified several areas that have limited information. Additional research and evaluation could help answer the following questions and fill remaining gaps in the evidence base. (What are 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?
  • Do primary safety belt laws increase or 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?
  • What are the cost-benefit, cost utility, and cost-effectiveness of interventions to increase safety belt use?
  • How can communities increase public acceptance of primary safety belt laws?

Study Characteristics

  • All of the included studies compared 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.