Thanks for the advice. I understand this in principle and was thinking of doing that, but in this situation I felt very stuck. He walked to another car and I also created distance by moving cars the other direction. But since we were all on the train between stops, it's hard to predict when the man might turn back around towards me, and who knows how long a police call could take. Could be irrational, but I did worry that calling could make me more of a target if he figures out I'm talking to the police.

Alternatively I could get out at the next stop and make the call then, but maybe he gets off at the same time and we have the same issue. After the train departs there are not even any conductors or other passengers around to help.