Half of Fatally Injured Young Drivers Are Under the Influence

According to a new study, half of all fatally-injured drivers aged 16 to 25 are driving under the influence of alcohol, marijuana or both. Driving under the influence is a very risky practice, and in addition to estimating its prevalence and underlining its risks, researchers from Columbia University's Mailman School of Public Health were interested in the effects that policy—particularly the suggestion that the legal drinking age should be reduced to 18—could have upon usage rates of alcohol and marijuana and thereby DUI risk. The study suggests that reaching the legal drinking age makes using both marijuana and alcohol more common rather than replacing marijuana use with alcohol.

Investigating DUIs in Fatal Car Accidents

The design of the study was fairly straightforward: researchers looked at data from fatal motor vehicle accidents involving young drivers between the ages of 16 and 25 from nine states. Chosen because they routinely test the blood or urine of drivers who die in crashes for substances, the states involved were California, Connecticut, Hawaii, Illinois, New Hampshire, New Jersey, Rhode Island, Washington and West Virginia. The researchers looked at nearly 7,200 accidents that took place between 1999 and 2011. Additionally, the researchers investigated whether there were any changes in the pattern of marijuana and alcohol use between those legally allowed to consume alcohol and those who were under 21.

Half of Fatally Injured Drivers Were Drunk, High or Both

The core finding was that 50.3 percent of the fatally-injured drivers from these states were either under the influence of alcohol, marijuana or both substances. Specifically, 36.8 percent had consumed only alcohol, 5.9 percent had used only marijuana and 7.6 percent had used both substances prior to the accident. This alone drives home a key point for young drivers: drinking or smoking pot prior to driving is incredibly dangerous and could lead to your death or that of others on the road.

The team then looked at the impact that age (specifically, being 21 or over and thus legally allowed to drink) had on the likelihood of alcohol use, pot use or both. The researchers found that those over 21 years of age were around 14 percent more likely to drink alcohol than those under 21, but they found little difference in risk of pot use, with the odds actually decreasing slightly, although this finding wasn’t statistically significant. For both alcohol and pot being in the driver’s system, there was a 22 percent increase in risk after age 21, but this again was only a slight difference.

It’s worth noting that the increase in risk for using both alcohol and pot together also wasn’t statistically significant. Understanding why is fairly simple: unless you can take data from everybody in your target population, there is a chance you’ll get a sample that isn’t quite representative. To counter for this, “confidence intervals” are used, which give a wider spread of possible values that will contain the true, whole-population average (in this case, the actual average risk of pot and alcohol use) 95 percent of the time. If the value for one group is within the confidence interval of the value for the other group, there may not be a difference at all—it could just be a chance result because of the limited sample size. In this case, the decrease in pot use after age 21 and the increase in alcohol and pot use weren’t significant for this reason. Both increases could well be real, but this study can’t rule out the influence of chance.

Drunk and Drug Driving—Risks Not Worth Taking

Regardless of the lack of statistical significance for most of the changes in use with age, the core finding that around half of all young drivers who die in crashes were under the influence speaks volumes. Most people are well-aware of the dangers of driving under the influence of alcohol: simply put, alcohol reduces your reaction time, negatively affects your decision-making ability and impairs your co-ordination, making driving while drunk an incredibly dangerous endeavor.

For pot, the risks are less well-publicized but just as severe. Other research has found that between 4 percent and 14 percent of all drivers injured or killed in motor vehicle accidents had THC (the psychoactive ingredient in marijuana) in their systems at the time of the accident. A study from Australia showed that when THC was found in the blood of the driver, he or she was more likely to be at fault for the accident, and the more THC found, the more likely the driver was to be at fault. Marijuana affects your perception of time and speed, reduces attentiveness and impairs your ability to use information from past experiences to guide your decisions. When alcohol and marijuana are combined, the effect increases dramatically.

More research in this area is needed, particularly investigating the effect of marijuana decriminalization or legalization on the number of drivers found with pot in their systems. Drug users need help and support instead of legal punishment, but taking a risk like driving under the influence is a very different issue that should be treated like the severe risk it is.

Posted on March 23rd, 2015
Posted in Teens

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