The difficulty of enforcing laws against driving while high

Abby McLean of Northglenn, Colo., stands near the stretch of U.S. 85 in Adams County where she was pulled over for a DUI check in September 2014. (Photo by Nathaniel Minor/CPR News)
This story starts with a stay-at-home-mom from the Denver suburbs.
Her name is Abby McLean. She’s 30 and lives in Northglenn, Colo. She was driving home from a late dinner with a friend two years ago when she came upon a DUI roadside checkpoint.
“I hadn’t drank or smoked anything, so I was like, &ls