Meth Use on the B-Line

I'm new to the twin cities and have started taking the bus to get to work. I take the B Line and have noticed a people actively smoking meth while on the bus. Most recently, I saw someone smoking from one of those folded pieces of foil, walk to the door, and exhale smoke while passing other riders. It got me a little nervous about second hand exposure.

Is this a common thing in the metro lines or is this more limited to the B Line?