Police, Bartenders, Passengers: How to Know When Someone is Too Drunk to Drive

  • In the U.S., 48 states and the District of Columbia have legal blood alcohol concentration (BAC) limits
  • The legal limits range from a .08 to a .10 percent BAC
  • Most people arrested for driving while intoxicated (DWI) have BACs greater than .15 percent
  • One study found that, using observation alone, police officers are unable to identify drinkers until they have reached high BACs

There is a huge difference between knowing if someone has been drinking, and knowing if they have had too much to drink. Could the person cavorting with an impromptu party hat earlier in the evening later cause a traffic accident? People such as bartenders, social hosts and police officers often have the responsibility, and sometimes the legal mandate, to make such an evaluation about someone else’s level of intoxication. A study in the June issue of Alcoholism: Clinical & Experimental Research examines the ability of police officers to identify individuals who might be too intoxicated to function.

"The ability of police officers to determine intoxication has several important applications," said John Brick, director of Intoxikon International Research and lead author of the study, "one of which is the prevention of DWI (driving while intoxicated) injuries. Yet it is no simple matter to determine if someone is too intoxicated to drive … until they are at a very high risk for injury. This study suggests that when someone is showing clear symptoms of alcohol impairment - enough to be rated too intoxicated to drive or to be served another drink - this person is well beyond the current definition of drunk driving in most states, and close to twice the legal definition of drunk driving in other states."

Driving is a multi-task endeavor, meaning that a driver must be able to handle several tasks at once. Although outward appearances vary with each individual’s ability to ‘hold their liquor,’ virtually all drivers are substantially impaired at a .08 percent blood alcohol concentration (BAC). Laboratory and on-road research has shown that most drivers, even experienced drivers, have significantly impaired braking, steering, lane changing, judgement and divided attention abilities at a .08 percent BAC. According to Mothers Against Drunk Driving, 48 states and the District of Columbia (D.C.) have current or pending laws that make it illegal to drive with a BAC above a certain limit. In 21 states, a .10 percent BAC is the legal limit. In 27 states and D.C., a .08 percent BAC is either the legal limit or pending gubernatorial signature. (Rhode Island’s law is not recognized and Massachusetts has none.)

In Brick’s study, New Jersey police officers were shown television-quality videotaped interviews with drinkers at low (.08 - .09%), medium (.11 - .13%) and high (.15 - .16%) BACs. The officers were then asked to answer questions about the subjects’ levels of intoxication, as well as their own confidence in the accuracy of their observations. Although the officers were very confident about their observations, they were generally unable to identify those individuals at risk for DWI until the drinkers’ BACs were in the high range. This is consistent, said Brick, with national statistics about DWI arrests. Typically, most people arrested for DWI have blood alcohol levels in the high range (greater than .15%)

"Police confidence," explained Edward Sponzilli, an attorney with the law office of Norris McLaughlin & Marcus, "is based on an honestly held belief that expert training and experience will make police more accurate in their assessments. However, what the authors of this study demonstrate is that police officers’ assessments are rarely based on observations alone, especially devoid of vehicle operation. The police in the study did not take into account the fact that their ability to observe was substantially restricted to videotape alone. As the authors noted, the raters were deprived of the sense of smell. It could also be added that observing casual conversation may not be adequate to judge balance dexterity, pupil dilation, or even flushness, depending on close-ups or other limitations of videotape. However, these limitations are not inconsistent with the context in which a social host, bartender, or potential passenger may observe an intoxicated person." In other words, even police officers - with all of their experience and training - cannot rely on observation alone to judge the degree of someone’s level of intoxication.

"A very important and practical implication of this study," said Brick, "is that if you see someone who looks impaired, they are probably drunk by any legal definition. Symptoms of intoxication and impairment such as slurred speech, inappropriate uninhibited behavior, difficulties walking or taking money out of a purse or wallet, are probably a good indication that the person has a BAC in the .15 percent or higher range. At that level, the risk for an accident is about 18 to 80 times higher than someone who is sober." Brick said that the range is due to other factors, such as age, gender and whether the accident involves one or more vehicles. "For example," he continued, "a young underage male with a BAC of .15 percent has a relative risk of having a single car accident that is about 15,000 times higher than a sober driver."

Another implication, said Sponzilli, is that in cases where a BAC is less than .15 percent, "to assume that an untrained or inexperienced person could be able, by observation alone, to assess the intoxication of another is invalid." Yet that is what some state laws require. "Some members of the general populace," said Sponzilli, "face legal liability when they fail to recognize intoxication in a variety of social settings. For example, the law imposes a duty not to entrust your car to a person who is under the influence of alcohol, which in New Jersey means someone whose BAC is at the .10% level. If an alcohol influence is found, then the car owner may face a six-months to one-year loss of license, and fines and penalties identical to that of the drunk driver. Similarly, in many states, a social host may be liable to accident victims as a result of their guest’s ingestion of alcohol to the point of intoxication."

"We clearly need better ways to identify people who are too intoxicated to drive," said Brick, a biological psychologist and also the senior author of a similar, earlier study. "Furthermore, these measures should be available to police and others when typical testing is not possible." Meanwhile, he added, "the bottom line of this research is that if someone looks visibly impaired, no matter how they say they feel, chances are they are far too intoxicated to leave your restaurant, bar, or home and drive safely. "

Funding for this Addiction Science Made Easy project is provided by the Addiction Technology Transfer Center National Office, under the cooperative agreement from the Center for Substance Abuse Treatment of SAMHSA.

Articles were written based on the following published research:

Brick, J., & Carpenter, J.A. (2001, May). The identification of alcohol intoxication by police. Alcoholism: Clinical and Experimental Research, 25(6), 850-855.