I think Baltimore's Light rail had to use a Grade at one point to clear a over head by one or two inches.
Rode the London Underground one day... there are grades going into and leaving a station. They were there to accelerate heavy cars leaving and to slow loaded ones to stop.
Also I suspect to stop flooding from coming up through the stations as well.
18 to 22% grades was about as much as I can stand outside of a roller coaster...
I still recall Cass. Some of those grades have to be in the 12% range... whew...