Yes, they do grow and the above screens are very impressive. However, if you scale them to the real word, they are still no more than small towns and nothing of that size would EVER have a subway system, it would just make no ecconomic sence. You need a CITY to warrent a subway and Train Fever doesnt have them, period.
Anyway, can, well, sort of, have subways. Just build a sunken staion. It’s expensive and the staion itself has to be open to the sky but can be done with all the track being underground.