blakistan asked:

...are there even ten transit systems in the US to begin with??

amtrak-official answered:

Yes

1. New York Subway
2. Amtrak
3. LIRR
4. Chicago L
5. BART
6. NJTransit
7. Septa
8. Metra
9. Metro North
10. Sound Transit

[amtrak-official]

Actually the DC metro is probably in 4th place so remove Sound transit and add in the DC metro