Massachusetts has legalized marijuana use, and many police departments are concerned about a rise in Marijuana DUI incidents and the possible risk to public safety. Still, marijuana use is hardly a new phenomenon, even if it just became legal. It’s been decriminalized for 8 years, there is still no legal retail supply increase, and their won’t be for a couple of years. So is little reason to believe there will be an epidemic of new pot smokers getting behind the wheel while high.
However, to the degree that it is a real public safety problem (which is debatable), actually proving that someone is too high to drive is a challenge for the police and prosecution and may get even tougher.