Impaired Driving Laws
under 21 drinking and driving laws

Under 21 Drinking and Driving Laws

Young drivers are less likely than adults to drive while impaired, but their crash risk is substantially higher when they do. Drivers are considered to be alcohol-impaired when their blood alcohol concentration (BAC) level is greater than 0.01.

About a quarter of car crashes with teens involve an underage driver who had consumed alcohol, according to a recent study published in Pediatrics. This number includes all deaths: not just the drivers, but also their passengers. Of those that died, one in four involved teen drivers under the legal limit. A goal of public policy should be to enact under 21 drinking and driving laws with no acceptable BAC level. The aim of these laws is help prevent impaired driving.

While other countries have seen progress in alcohol-related crash deaths, the US as a whole has not. The US legal drinking limit is higher than in other countries, affecting the safety of all drivers, and among young drivers there is no safe limit for alcohol. It has long been known that any amount of alcohol is dangerous for young drivers and that the risk increases with greater amounts of alcohol in their system.

Alcohol affects reaction times and ability to drive safely as do other substances, like marijuana and prescription pills, that affect alertness. Youth who drive under the influence of alcohol or drugs put themselves and others at risk.  Adolescent drinkers are also more likely to ride as passengers of impaired drivers.

The dangers associated with alcohol and driving are exacerbated with the sadly common situation of binge drinking, a pattern of drinking that brings the person’s blood alcohol concentration (BAC) to 0.8 grams percent or above in a short time – typically five drinks for men and four drinks for women in about two hours, according to the Centers for Disease Control and Prevention. This is a common dangerous practice, unfortunately, among adolescents who “pre-game” before going out.

National Minimum Drinking Age Act

Until the 1980s, each state had its own laws determining the minimum drinking age. This led to the creation of “blood borders,” where teens would drive to states with lower drinking ages and be involved in fatal crashes on the return trip. In 1984, following an overall increase in alcohol-related traffic fatalities and injuries, Congress passed the National Minimum Drinking Age Act (NMDA), or the Federal Uniform Drinking Age Act, requiring states to legislate and enforce 21 as a minimum age for purchasing and publicly possessing alcoholic beverages. Since July 1988, all 50 states and the District of Columbia have enforced a legal drinking age of 21. According to the National Highway Traffic Safety Administration (NHTSA), there has been a 16 percent decrease in motor vehicle crashes since the NMDA went into effect.

Zero Tolerance Laws

Since 1988, all 50 states and the District of Columbia have implemented zero tolerance laws that set a limit of 0.02 percent BAC or lower for drivers under age 21. The 0.02 limit is equivalent to about one drink for the average person.

Although zero tolerance laws have been challenged based on their effectiveness, they have helped to significantly reduce the number of fatal crashes involving intoxicated young drivers. The first four states to reduce the legal BAC limit for young drivers (Maine, North Carolina, Wisconsin, and New Mexico) experienced a 34 percent decline in nighttime fatal crashes among young drivers. This decline was about one-third greater than a similar decline in four nearby states. An additional study of 12 states that passed zero tolerance laws reported a 20 percent reduction in single-vehicle nighttime fatal crashes among 15- to 25-year-old drivers. 

Alcohol Policy Scale (APS)

To identify associations between alcohol policy environments and crash deaths among young people in the US, researchers used the Alcohol Policy Scale (APS) to rate alcohol policies and implementation in all 50 states and Washington DC. For each state and year, a panel of policy experts independently assessed each policy with regard to its efficacy for reducing excessive drinking or alcohol-related harm and the degree of legislative implementation for each policy.

States were ranked on how restrictive their alcohol policies were, including higher alcohol taxes and zero-tolerance policies for drivers younger than age 21. Then they cross-referenced the APS scores with crash data from the Fatality Analysis Reporting System (FARS). A 10 percentage-point increase in a state’s APS score was associated with a 9 percent decrease in the odds of alcohol-related crash fatalities. This research shows the effect of comprehensive alcohol policies on alcohol-related MVC fatalities among young people.

Marijuana and Driving

The District of Columbia and 33 states currently have laws broadly legalizing marijuana in some form. As more states pass legislation for legalization of marijuana either for recreational or medical use, understanding how THC (tetrahydrocannabinol), the active ingredient in marijuana, impacts driving should be a priority for the scientific community. Although the research is limited, generally accepted results reveal a two-fold risk of a motor vehicle crash among drivers with any THC in the bloodstream.

While laboratory studies of people with THC in their bloodstream do not support significant impairment on single tasks, such as memory, addition, or subtraction, there may be more significant impact on multitasking and handling unexpected events (which are critical components of safe driving).

Detecting clinically significant levels of THC in the body can be complicated. Urine levels, which in many states are equated to blood levels (and are both illegal), can reflect past use and may not reliably detect people who are actually "high". Some researchers suggest that resources are better directed toward reducing drinking and driving or reducing the mixing of alcohol and marijuana while driving.

Teen drivers should be especially wary of driving after taking any substance that may be mind-altering, including marijuana. The tasks required for driving are complex and require much higher order thinking than they realize.

To learn more about under 21 drinking and driving laws in your state, visit the Mothers Against Drunk Driving website.

To learn more about legalizing marijuana laws in  your state, visit the website.

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