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Motor Vehicle Injury – Alcohol-Impaired Driving: Maintaining Current Minimum Legal Drinking Age (MLDA) Laws


What the Task Force Found

About The Systematic Review

The Task Force finding is based on evidence from a systematic review of 33 studies (search period 1966 - 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, all 50 states had set their minimum legal drinking age laws at 21.

Summary of Results

Thirty-three studies qualified for the systematic review.

  • Most of the studies assessed the effects of changes in the MLDA from ages 18 to 21 or vice versa.
    • Effects of raising the MLDA: crash-related outcomes decreased by median of 16% (14 studies; 1 study evaluating fatal crashes among 16-17 year olds was not included in the summary effect measures)
    • Effects of lowering the MLDA: crash-related outcomes increased by median of 10% (9 studies)
    • Estimated effect of raising the MLDA by 3 years (from 18 to 21) from regression-based studies: crash-related outcomes decreased by a median of 12% (9 studies)
  • Effects were stable over follow-up times ranging from 7 to 108 months.

Summary of Economic Evidence

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


  • Results should be applicable to all drivers 18–20 years of age.
  • Results are based on studies from the U.S., Australia, and Canada, however, and may not apply to countries with different alcohol consumption or driving patterns.

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

Research Issues – Laws

  • How do variations in enforcement levels influence the effectiveness of laws to reduce alcohol-impaired driving?
  • What are the independent effects of publicity on the effectiveness of laws to reduce alcohol-impaired driving?
  • Does public compliance with new laws change in a predictable manner over time?

General Research Issues

The following outlines evidence gaps for reviews of these interventions to reduce alcohol-impaired driving: 0.08% Blood Alcohol Concentration (BAC) Laws; Lower BAC Laws for Young or Inexperienced Drivers; Maintaining Current Minimum Legal Drinking Age (MLDA) Laws; Sobriety Checkpoints (archived); Intervention Training Programs for Servers of Alcoholic Beverages (archived).

General Questions

  • How do interventions to reduce alcohol-impaired driving interact with each other (e.g., 0.08% BAC laws and administrative license revocation)?
  • What effects do these interventions have on long-term changes in social norms about drinking and driving?


Questions remain about possible differences in the effectiveness of each intervention for specific settings and subgroups. For example:

  • Are these interventions equally effective in rural and urban settings?
  • Are these interventions equally effective when applied to populations with different baseline levels of alcohol-impaired driving?
  • Does targeting publicity efforts to specific subpopulations (e.g., young drivers, ethnic minorities, men) improve the effectiveness of interventions to reduce alcohol-impaired driving?

Other Positive or Negative Effects

Few other positive and negative effects were reported in this body of literature. Further research about the following questions would be useful:

  • What proportion of youths charged with violating zero tolerance laws had BAC levels elevated enough to warrant a more serious drinking-driving offense?
  • Do interventions to reduce alcohol-impaired driving reduce other forms of alcohol-related injury?

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 reduce alcohol impaired driving?

Barriers to Implementation

Several of the interventions reviewed face barriers to effective implementation. Research into the following areas may help to overcome these barriers:

  • What role can community coalitions play in removing barriers to implementing interventions designed to prevent alcohol-impaired driving?
  • What are the most effective means of disseminating research findings about effectiveness to groups that want to implement interventions?
  • What forms of incentives (e.g., insurance discounts) are most helpful for increasing management and owner support for server intervention training?
  • How can the costs of interventions to prevent alcohol-impaired driving be shared or subsidized?
  • What situational and environmental influences help or hinder the implementation of server intervention training?

Study Characteristics

  • Studies were conducted in the U.S., Canada, Australia, and Canada.
  • Most studies in the review assessed the effect of changes in the minimum legal drinking age from 18 to 21 years or vice versa.
  • Included studies reported the following outcomes: fatal injury crashes or crash fatalities; fatal and nonfatal injury crashes, or other crash types.


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.