I disagree. Marijuana can impair reflexes significantly, at least for some individuals. My high school drivers education class (1979) had an electronic device used to measure brake reflex time. The device had simulated accelerator and brake pedals. A red lamp would light to signal the need to brake. I believe the average response time for most teens was around 250ms. I smoked pot nearly everyday during this period of my life. On the day our class was put to the brake response test I showed up high, as usual. I scored over 1 second on the response test. The instructor at first thought I was putting him on. He reset the device and had me try again. The response time was the same. I'll also admit that during this time I had episodes where I would "zone out" while driving high on pot. I would not remember a significant portion of the drive I had just undertaken.

My read of the article referenced is that current measurement techniques for Marijuana do not accurately correlate with driver impairment. That's not the same thing as stating Marijuana impaired drivers are safer than ones intoxicated with alcohol.