According to a new federal study from the National Highway Traffic Safety Administration (NHTSA), drivers that are under the influence of marijuana are significantly less likely to be in a collision than drivers who are under the influence of alcohol.
The study confirms what I’ve previously said on this blog, namely that, although marijuana does affect reaction times, the effects of alcohol on driving ability are far more likely to cause an accident.
The study, which is “the first large-scale [crash risk] study in the United States to include drugs other than alcohol,” analyzed over 10,000 drivers over a 20 month period.
According to the study, the risk of an accident for someone with a blood alcohol content of 0.08 percent was twice that of someone who was sober. Those with a blood alcohol content of 0.10 percent were six times more likely to be involved in an accident. The risk of an accident rose as high as 12 times for those with a blood alcohol content of 0.15 percent.
The numbers for the risk of an accident with marijuana use were significantly less.
Although drivers who had a THC in their system were 25 percent more likely to be involved in an accident, once the researchers accounted for other variable such as sex, age, and race/ethnicity, the risk ratio for marijuana use was no longer statistically significant.
“This analysis shows that the significant increased risk of crash involvement associated with THC and illegal drugs…is not found after adjusting for these demographic variables. This finding suggests that these demographic variables may have co-varied with drug use and accounted for most of the increased crash risk. For example, if the THC-positive drivers were predominantly young males, their apparent crash risk may have been related to age and gender rather than use of THC.”
In other words, the study suggests that the risk of an accident when a driver had THC in their system could be attributed to variables other than the presence of THC. And while this may be true, the NHTSA warns, “these results do not indicate that drug use by drivers is risk-free.”
However, the NHTSA also admits that, although it tested for the accident risk of drivers with THC in their systems, the presence of THC in not necessarily an indicator of actual impairment at the time of driving. THC can stay in a person’s system weeks after using marijuana and well after the person is impaired by its use.