The anti-pot group Project SAM claims drug test data show that marijuana legalization in Washington, approved by voters in that state at the end of 2012, already has made the roads more dangerous. The group notes with alarm that the percentage of people arrested for driving under the influence of a drug (DUID) who tested positive for marijuana rose by a third between 2012 and 2013. “Even before the first marijuana store opens in Washington, normalization and acceptance [have]set in,” says Project SAM Chairman Patrick J. Kennedy. “This is a wakeup call for officials and the public about the dangerousness of this drug, especially when driving.”
In truth, these numbers do not tell us anything about the dangerousness of marijuana. They do not even necessarily mean that more people are driving while high. Furthermore, other evidence suggests that legalizing marijuana could make the roads safer, reducing traffic fatalities by encouraging the substitution of marijuana for alcohol.
According to State Toxicologist Fiona Couper, the share of DUID arrestees in Washington whose blood tested positive for THC, marijuana’s main psychoactive ingredient, rose from 18.6 percent in 2012 to 24.9 percent in 2013. That’s an increase of more than 33 percent, as Project SAM emphasizes with a scary-looking bar graph. At the same time, the total number of DUID arrests in Washington rose by just 3 percent, about the same as the increases seen in the previous three years, while DUID arrests by state troopers (see table below) fell 16 percent.
These numbers do not suggest that Washington’s highways are awash with dangerously stoned drivers. So why the substantial increase in positive marijuana tests? Lt. Rob Sharpe, commander of the Washington State Patrol’s Impaired Driving Section, notes that additional officers were trained to recognize drugged drivers in anticipation of marijuana legalization. So even if the number of stoned drivers remained the same, police may have pulled over more of them as a result of that training.
Another point to keep in mind is that a positive THC test does not necessarily indicate a driver is impaired. The current cutoff for these tests in Washington is two nanograms of THC per milliliter of blood, less than half the state’s new per se standard for DUID, which itself is not a very good indicator of impairment, especially for regular users. Sharpe concedes that the increase in positive tests could simply reflect an overall increase in marijuana use. When cannabis consumption becomes more common or more frequent in the general population, the percentage of DUID arrestees who test positive for THC is apt to rise, even if the percentage who are actually impaired does not.
– Read the entire article at Forbes.