Updated March 04, 2015.
National transportation statistics show a significant decrease in drunk drivers on the road, but a big increase in drivers under the influence of drugs. But, the raw statistics may fall short of proving that increased drugged driving equals more traffic crashes and fatalities on the highways.
The numbers do show that drivers who smoke marijuana are more likely to be in vehicular crashes, but that increased risk could be due in part because most drivers using marijuana are in a group already at a higher risk for crashes - young males.
Roadside Survey Voluntary and Anonymous
In what the National Highway Traffic Safety Administration calls "groundbreaking" studies, the nation's crackdown on drunken drivers has been shown to be very effective - with the number of drunk drivers on the road dropping by 80% since the early 1970s.
The National Roadside Survey, has been conducted only five times in the past 40 years. It is a voluntary, anonymous survey that gathers information from dozens of locations across the country.
Multiple roadside signs alert drivers that a voluntary survey site is ahead. Drivers are free to keep driving or pull into the site to get more details, but the signs offer them a fee (up to $60) for their time to take the survey.
They are told that the survey is completely voluntary and entirely anonymous. About 9,000 weekend, nighttime drivers took part in the 2014 survey.
Huge Reduction in Drunk Driving
Findings of the 2014 National Roadside Survey included:
- 8% of weekend, nighttime drivers had alcohol in their system.
- 1.5% had a blood-alcohol content of .08 or higher.
- This number is down 30% from 2007.
- The number is down 80% from the first survey in 1973.
Significant Increase in Drugged Driving
But it wasn't all good news in the 2014 survey results. The study also found:
- 20% of weekend, nighttime drivers had drugs in their system.
- This number is up from 16.3% in 2007.
- Drivers with marijuana in their system increased 50% since 2007.
- 12.6% of weekend, nighttime drivers had marijuana in their system.
- 15% of drivers tested positive for at least one illegal drug.
Crash Risk Study
The second NHTSA survey was the largest of its kind ever conducted to determine how alcohol and drug use is linked to a greater risk of auto crashes. The study was conducted in Virginia Beach over a 20-month period.
Researchers gathered information from more than 3,000 drivers who were involved in auto crashes and compared that to a group of 6,000 drivers who were not involved in a crash.
The researchers wanted to see how alcohol use and the use of prescription and illegal drugs affected the risk of being in a crash, but the only drug that showed up in the study participants was marijuana.
Marijuana was the only category of drug for which study findings reached statistical significance, the NHTSA said.
Of the 3,000 crash-involved drivers, 66% were involved in property damage only crashes, 33% were involved in crashes that caused injury, and 1% were involved in fatal crashes.
Marijuana Users More Likely to Crash?
Findings of NHTSA crash risk study included:
- Drivers with an .08 alcohol level were 4 times more likely to crash compared to sober drivers
- Drivers with an alcohol level of .15 were 12 times more likely to crash.
- Marijuana users were 25% more likely to crash.
- Age and gender could account for the increased risk for marijuana users.
The 25% increase in risk of having an auto crash for marijuana users was seen in only one group - young males, a group that is statistically at a higher rate of having highway crashes. Therefore, the NHTSA plans more research to determine how marijuana affects drivers.
Previous studies using driving simulators and test tracks have found that at sufficient dosages levels marijuana affects the risk of auto crashes.
The 2015 crash-risk study did not control for factors such as the amount ingested, the potency ingested, prior experience with marijuana, and individual differences in response to marijuana.
The trend toward increased drugged driving poses challenges for those involved in highway safety.
"Researchers have developed a deep body of knowledge about the link between drinking, driving and risk. We know drunk driving kills," NHTSA Administrator Mark Rosekind said in a news release. "The combined message of these two surveys is that our work to understand and combat drunk driving is paying off, but that we have much to learn about how illegal drugs and prescription medicines affect highway safety – and that developing that knowledge is urgent, because more and more drivers have these drugs in their systems."
Sources:
National Highway Traffic Safety Administration. "Results of the 2013–2014 National Roadside Survey of Alcohol and Drug Use by Drivers." Traffic Safety Facts: Research Note February 2015.
National Highway Traffic Safety Administration. "Drug and Alcohol Crash Risk Study." Executive Summary February 2015.