So sorry if this already was a thing, but I was in Metro City again (like always when I play 3) and even after all these years, I JUST found out that the subway was part of the course. I've always jumped the subway since that's on the main line and I know 3 or 4 shortcuts on the course (like going through the middle over the billboards when it splits and like 10 seconds later jumping the little ramp over the edge or the curves) but I never got to the subway. I jumped bad, smacked a few buildings (unfortunately dropping me to 6th) and all of a sudden BAM subway tunnel, and then the rails of the car were grindable and then it just carries you through a tunnel...I was still in 6th after that but luckily I ended in 3rd.
On a side note, shattering the glass near the end is oh so satisfying...