I remeber reading an anecdote that once upon a time, in the 70s, I believe, the same was done in the Soviet Union. After a rather short time, the decision was reverted, and not because of the economical costs: the public transport never was profitable or even self-sustaining to begin with, and dropping the 4 copecks price of a ticket didn't really changed much.

No, the reason was that the amount of pickpocketing in the public transport skyrocketed: apparently, having to pay 4 copecks on every boarding really did inconvenience the pickpocketers a lot. A useful reminder that every public policy change can have completely unforeseen consequences.