I moved here from a city that still had a few at-grade light rail systems running.  Every time there was a car accident that needed investigation; a fire; a water main break; road construction; or anything else that required a road closure, the line came to a dead halt.  There are no alternatives when a street level system cannot move forward.  These trains also must stop for all red lights, slowing progress.  Trust me when I say that cars also do their best to get in the way; I've seen it multiple times, and pedestrians are not safe when exiting the trains and attempting to cross the street.