C-Train Etiquette

I take C-train every day because of going to university.
And I found some rule and etiquette on C-train.
First, no smoking and no litter are maybe written rules.
Second, men don't sit down next to women. I think this is etiquette rather than unwritten rules and only some gentlemen follow it.
Rules and etiquette are differ from country, prefecture, city.

I think we are confused.
But we should                when in Rome, do as the Romans do.