Since Washington legalized the adult use of recreational marijuana, many have asked the Washington Traffic Safety Commission how this change may impact traffic safety. The commission took the first step toward understanding the issue by releasing a new report providing a detailed examination of marijuana positive drivers involved in deadly crashes.
This is the first time in Washington that crash data on marijuana positive drivers has distinguished between drivers who test positive for THC, the impairing substance in marijuana, and those who have residual marijuana, called carboxy, in their system from prior use which may have occurred days ago. This study categorizes marijuana positive drivers into mutually exclusive categories based on the total results of their blood tests.
In Washington, impaired driving is the leading factor in traffic deaths. This includes drivers who are impaired due to alcohol, marijuana, and other drugs—prescription or illegal.
Most drivers received both alcohol and drug testing. The State Toxicology Laboratory tested blood samples for both alcohol and drugs for 1,773 drivers involved in deadly crashes between 2010 and 2014. Of these 1,773 drivers tested, nearly 60 percent (1,061) were positive for alcohol, marijuana, or drugs.
Most drivers who were tested had multiple substances in their system. Among drivers with positive test results, the largest percentage showed combinations of alcohol, marijuana and other drugs. Approximately one-third revealed alcohol only (34 percent), and eight percent tested positive for marijuana only.
Marijuana is the most frequently found drug. Not including alcohol, marijuana continues to be the most frequently-occurring drug among drivers involved in deadly crashes. By itself or in combinations with alcohol and other drugs, 349 drivers tested positive for marijuana.
The report further separates these drivers by those positive for THC and those positive for carboxy.
More drivers tested positive for THC. In 2014, of the 89 drivers who tested positive for marijuana 75 of them (84 percent) were positive for THC. This is much higher than 2010 when 81 drivers were positive for marijuana and 36 (44 percent) of those were positive for THC.
Half of THC positive drivers are above 5 ng/ml. In 2014, among the 75 drivers involved in deadly crashes who tested positive for THC, about half exceeded the 5 ng/ml per se limit.
THC is increasing while alcohol is decreasing, the report says. The 75 THC-positive drivers in 2014 comprised the highest number of THC-positive drivers in any year during the five-year period studied. The 51 drivers who only had alcohol in their systems (and were over the per se limit) in 2014 were the lowest number of such drivers in the study period.
Most THC positive drivers are young men. When looking at drivers positive for THC, either THC-only or in addition to alcohol above the per se limit, nearly 40 percent were men ages 16-25.
The report also notes that drivers combining marijuana and alcohol showed increased risk. Drivers who combined alcohol and marijuana were frequently unbuckled, unlicensed and speeding.
THC positive drivers were more likely to be involved in daytime crashes. A majority of deadly crashes involving drivers with THC alone, or in combination with other drugs, except alcohol, occurred during the daytime hours. A majority of deadly crashes involving drivers with alcohol above the per se limit, alone or in combination with marijuana or other drugs, occurred during the nighttime hours.
The full report, “Driver Toxicology Testing and the Involvement of Marijuana in Fatal Crashes, 2010-2014,” is available here.
For more information on the Target Zero campaign, aimed at ending traffic deaths and serious injuries in Washington by 2030, visit www.targetzero.com.