Not a problem.  You are much more likely to see someone looking down at their cell phone or texting than someone high on marijuana!

That I see constantly.  Saw one young lady doing that in the right lane as I was a passenger in the left lane on Main Street yesterday.  Pretended to take her picture with my cell phone; thought she was gong to drive into a nearby business when she spotted me!  Bad idea to wake up one of them while they are on their phone!