In the first study, researchers from New York and South America collaborated on an analysis of traffic fatality data from Colorado and Washington. They found that since recreational cannabis laws were relaxed, road deaths in Colorado increased by an average of 75 excess fatalities per year. No increase was noted in Washington, which the authors say may reflect differences in how widespread recreational cannabis stores were between the two states at the time of the investigation.
The second study by New York Medical College and Harvard University researchers added another two more states that allow recreational weed – Oregon and Alaska. By extrapolating data from these four states they calculated that if every state legalized recreational cannabis, an extra 6,800 people would die each year in traffic accidents throughout the whole of the USA. They found an increase of 2 deaths per billion miles traveled, when comparing with 20 states without those laws.
Previous research has shown those who drive under the influence of cannabis have decreased reactions and are more likely to weave across lanes. Marijuana combined with alcohol use is associated with greater levels of driving performance impairment than either substance alone.
It’s a complicated picture though: while recreational cannabis may be associated with more road deaths, medicinal cannabis appears associated with fewer traffic fatalities. It’s theorized that people taking prescribed cannabis for specific medical conditions may still drive, but are more likely to stay off alcohol completely.
An accompanying editorial to the two JAMA Internal Medicine studies said: “Despite mixed findings, these studies provide much needed research on cannabis use and driving, while acknowledging that such retrospective analyses inherently lack precise control over the range of factors that can affect crashes across state populations during a period of time”.
