This cannabis user was arrested for DUI, yet his driving was fine — a clash of science and law that’s on the rise

PHILADELPHIA -- Patrick Murphy saw the flashing lights come on behind him on State Route 115, and he immediately knew what it was about. He was on his way to get an estimate to fix a broken headlight, but it was the day before Thanksgiving, typically a big day for traffic enforcement. Of all the bad luck, a Pennsylvania state trooper had spotted the damage first. Murphy didn’t know that his headlight was just the start of his problems that day in 2017. He suffers from chronic pain and PTSD, and while visiting relatives in Massachusetts six days earlier, he used cannabis to get relief. Murphy’s...