SoylentNews

Hugh Pickens writes:

As states liberalize their marijuana laws, public officials and safety advocates worry that more drivers using the drug will lead to a big increase in traffic deaths. Now The Guardian reports that it appears that unlike alcohol, drivers using marijuana tend to be aware that they are impaired and try to compensate by driving slowly, avoiding risky actions such as passing other cars, and allowing extra room between vehicles. In Washington State, there was a jump of nearly 25% in drivers testing positive for marijuana in 2013 – the first full year after legalization – but no corresponding increase in car accidents or fatalities. When adjusted for alcohol and driver demographics, a study by the Pacific Institute for Research and Evaluation found that otherwise sober drivers who tested positive for marijuana were slightly less likely to have been involved in a crash (PDF) than drivers who tested negative for all drugs. “We were expecting a huge impact,” says Eduardo Romano, lead author of the study, “and when we looked at the data from crashes we’re not seeing that much.”

But another recent study that used similar data to assess crash risk came to an opposite conclusion. When Columbia University researchers compared drivers who tested positive for marijuana in a roadside survey with state drug and alcohol tests of drivers killed in crashes, they found that marijuana alone increased the likelihood of being involved in a fatal crash by 80% (PDF). But because the study included states where not all drivers are tested for alcohol and drugs, a majority of drivers in fatal crashes were excluded, possibly skewing the results. Also, the use of urine tests rather than blood tests in some cases may overestimate marijuana use and impairment. “We see the legalization of marijuana in Colorado and Washington as a wake-up call for all of us in highway safety,” says Jonathan Adkins. "We don’t know enough about the scope of marijuana-impaired driving to call it a big or small problem.