A new study by the National Institute of Drug Abuse (NIDA) funded, in part, by the federal government, confirms what most cannabis advocates and users already know; alcohol impairs driving far more than marijuana.
The study examined 18 “occasional cannabis consumers” (13 men, ages 21-37 yrs), who stated they had used marijuana at least once in the past month but no more often than 3 days a week. The test subjects took a 45 minute driving simulator test after vaping marijuana, drinking alcohol, or taking a placebo. The test was partly designed to measure how many times the car left the lane, weaving in the lane, and the speed of the car.
The researchers are quoted as saying…
[Alcohol] “significantly increased lane departures/minimum and maximum lateral acceleration; these measures were not sensitive to cannabis” [Stoned drivers] “may attempt to drive more cautiously to compensate for impairing effects, whereas alcohol-influenced drivers often underestimate their impairment and take more risk.”
“alcohol, but not marijuana, increased the number of times the car actually left the lane and the speed of the weaving.”
Similar Fed Funded Study From November 1993: The National Highway Traffic Safety Administration did another study going back more than 20 years. The “Marijuana and Actual Driving Performance” report dated November, 1993 was performed by researchers at University of Limburg, The Netherlands, and sponsored by the U.S. Dept of Transportation.
Unlike the recent study, this one was performed with real cars and “in the presence of other traffic”.
Their conclusion is quoted below (edited with highlights):
This program of research has shown that marijuana, when taken alone, produces a moderate degree of driving impairment which is related to the consumed THC dose. The impairment manifests itself mainly in the ability to maintain a steady lateral position on the road, but its magnitude is not exceptional in comparison with changes produced by many medicinal drugs and alcohol. Drivers under the influence of marijuana retain insight in their performance and will compensate where they can, for example, by slowing down or increasing effort. As a consequence, THC’s adverse effects on driving performance appear relatively small.
Link to the Full Report: “Marijuana and Actual Driving Performance“
Marijuana Does Affect Driving At Levels
The recently released study does indicates that marijuana at levels can affect driving, with a reduction in peripheral vision (i.e. “tunnel vision”) noted as a main affected measure.
The THC level in the blood higher than 13.1 nanograms per milliliter of blood had an impact on weaving similar to blood alcohol concentration of 0.08 percent (most widely used cutoff for driving in most states).
Issue Of Testing THC Concentration In Drivers
One of the problems faced by the researchers was trying to accurately and timely measure the level of THC in the test subjects. Currently, the most accurate test for THC is a blood test, but as the researchers noted, “THC concentrations drop rapidly during the time required to collect a blood specimen in the U.S., generally within two to four hours.” An oral roadside saliva test is available but is currently not precise enough to use for legal purposes.
Improvement Needed In Legal Definition of “Driving Stoned”
Current “concentration-based” marijuana driving laws face a myriad of problems. States like Colorado and Washington have established a legal threshold of 5 nanograms, which is less than half of the 13.1 nanograms for impairment noted in the current study. And trying to get a timely reading of a driver’s THC level will require new tests than what is currently available.
The issue of driving while high will only get bigger as more states legalize the use of marijuana. Similar to industries that self-regulate, cannabis advocates must accept that driving stoned at certain levels should not be allowed and must help devise a sensible and fair solution that addresses all users; not just occasional user but also the heavy and first time users.
Drivers Stoned on Marijuana Test Their Driving Skills Video
The following is a CNN video from a few years back…