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Alcohol Isn't the Only Way to Impair Your Driving

Distraction in the car, marijuana and medications also can be deadly

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Whether a birthday, holiday or another celebration, numerous events throughout a year can lead to impaired driving. However, alcohol isn't the only substance that drivers should be cautious about before getting behind the wheel.

Impaired driving remains a major highway safety problem nationwide. Older drivers often face declines in vision, mental acuity and motor function. The addition of alcohol or other drugs adds an even greater risk to the safety of themselves and others, says Joe Feese, communications director at the Governors Highway Safety Association (GHSA).

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"Mature drivers — those age 65 and over — represent a growing segment of America's licensed drivers and face an increased risk of traffic-related injuries and fatalities. In 2017, [more than 6,800] people 65 and older were killed in motor vehicle traffic crashes, according to the National Highway Transportation Safety Administration [NHTSA],” Feese said.

In 2018, the deaths topped 6,900, a number that has been increasing steadily since 2011, according to the NHTSA's Fatality Analysis Reporting System. Drinking is the leading cause of impairment while driving, but drivers need to be aware of how other substances can affect their safety.


Effects of blood alcohol

The concentration of alcohol in the blood is generally measured in percentages, so a level of 0.08 percent is 0.08 grams of alcohol per deciliter of a person’s blood.

• Zero percent. Only safe level

• 0.01 to 0.03, impairment begins. Concentration, judgment, reflexes and vision start to become affected.

• 0.04 to 0.07, risk of crash. Greater effects on concentration, judgment, reflexes and vision. Effects are increased when combined with fatigue, illness, other drugs, poor driving conditions or stress.

•0.08 to 0.11, increased risk of crash. Illegal in every state. The risk of crash is 6 to 10 times greater than at zero percent blood alcohol, and the level of impairment is greatly increased.

• 0.12 to 0.15, very high risk of crash. Mental functions, motor skills and vision are severely impaired.

• 0.16 or more, extreme crash risk. Unconsciousness may come at  0.25 to 0.35. Death may occur at about 0.35 to 0.45 blood alcohol content.

As you get older, the conventional wisdom of consuming one drink per hour to drive safely might need to be reconsidered. Older adults may be more susceptible to the effects of alcohol on driving performance compared with those ages 25 to 35, a 2014 study from the University of Florida found.

As the body ages, its ability to break down alcohol decreases. Therefore, the alcohol stays longer in an older person's body. Blood alcohol content can continue to rise for a time after the last drink is consumed.

About a third of all traffic crash fatalities in the United States involve drunk drivers. Men are more likely than women to be driving in fatal crashes.

In 2017, 21 percent of men were drunk in these crashes, compared with 14 percent of women, according to the NHTSA.

To help prevent a crash, the Centers for Disease Control and Prevention (CDC) suggests:

• Designate a nondrinking driver
before anyone in a group starts drinking.

• Don't let your friends drive impaired.

• Get a ride home, use a ride-hailing service or call a taxi if you have been drinking or using drugs.

• Remind your guests to designate their sober driver if you're having a party in which alcohol will be served, to offer alcohol-free beverages and to make sure all guests leave with a sober driver.

• Don't believe myths that caffeine will sober you up or that driving is safe if words are not slurred.

Remember, one drink is defined as one 12-ounce beer or wine cooler, one 5-ounce glass of wine or 1.5 ounces of 80-proof distilled alcohol.


Cellphone use among drivers is a growing cause of accidents. During daylight across America, about 481,000 drivers are using cellphones while driving, the NHTSA says.

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As a result, distracted drivers kill about nine people and injure more than 1,000 each day, according to the CDC. To minimize the problem:

• Pull over to a safe place if you need to text or talk on the phone. Set rules for yourself and your household regarding distracted driving.

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• Avoid a ticket. Although federal law does not ban using a mobile phone while driving, all states but three — Missouri, Montana and Texas — have passed legislation prohibiting the use of handheld phones or text messaging while driving. Missouri and Texas do have restrictions on young drivers.

• Lower the volume on your phone to zero (silent). Or leave it somewhere in the car where you can't reach for it while driving if you think you may be tempted to check for messages.

• Avoid calling or sending texts to people if you know they are driving.

Cellphones aren't the only distraction. Make sure to keep the radio volume down and avoid multitasking, such as drinking, eating, reading or smoking behind the wheel.


With an increasing number of states legalizing marijuana, remember that THC, the drug's psychoactive component, impairs driving.

Marijuana products, including edibles, have varying THC concentrations, so a dose of one product may cause greater impairment than a dose of a different product. Sometimes different batches of the same type of edible vary in their amount of THC.

After smoking, THC concentrations fall to about 60 percent of their peak within 15 minutes and to about 20 percent of their peak 30 minutes later. However, impairment lasts two to four hours, according to a report from the GHSA, which cited a U.S. Department of Health and Human Services study.

The buzz you get from THC-infused edibles can last longer, depending on the timing of your most recent meal, prescriptions you take or simultaneous alcohol use, according to Denver Public Health, a nonprofit that partners with the Denver Department of Health & Environment to provide some services. As with alcohol, a “dose” of THC, which Colorado defines as 10 milligrams, can affect two people with different tolerances differently.

Alcohol is far simpler because it is quickly absorbed into the body, and impairment is directly related to blood-alcohol content.

Abbott, an Illinois-based company that developed SoToxa, a handheld analyzer that aids police in identifying drug-impaired drivers, found:

• 90 percent of boomers agree that law enforcement needs a way to quickly test a driver for being under the influence of drugs.

• 72 percent of boomers are concerned about an increase of drugged driving crashes with more states legalizing recreational marijuana.

• 66 percent of boomers do not believe enough is being done to stop drugged driving.

• 19 percent of boomers personally know someone who was in a crash caused by a driver high on drugs.

SoToxa, used in the U.S. and Canada, analyzes saliva and within five minutes can indicate if a driver has used marijuana and other drugs.

"Roadside testing also helps deter people who have consumed cannabis … from getting behind the wheel in the first place,” says Fred Delfino, senior law enforcement liaison at Abbott. “If a potentially impaired driver knows they could get caught, they'll think twice about driving high."


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Drug-impaired driving is more complex than alcohol-impaired driving.

"Older adults tend to take more medications, and medication can impact response time. Given these potential side effects of medications, it's important that older adults discuss these issues with their doctors when medications are prescribed,” GHSA's Feese said.

A surprising number of legally obtained and over-the-counter medications can affect a person's ability to drive. Ten percent of daytime weekday drivers surveyed tested positive for prescription or over-the-counter drugs, according to the 2013-14 National Roadside Survey from NHTSA.

Such drugs include allergy and cold medicines, antidepressants, opioids and sleep aids. They can cause side effects such as blurred vision, drowsiness and nausea, all of which can put motorists at risk.

Take note of warnings against “operating heavy machinery.” That includes cars. Some medications may not cause impairment on their own; however, when you take them with a second medication or with alcohol, they may cause impairment.

"If you feel different, you drive different,” NHTSA officials say.

Editor's note: This article, originally published December 23, 2019, has been updated to include the partnership between Denver Public Health and the Denver Department of Health & Environment.

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