It's important to note that no train system in the world is covered by fairs. They are always subsidized by the state. In most cities, fairs make up 20% ~ 30% of costs (tolls are about the same for toll roads).

Cities with expensive transit typically have mandates that x% of costs must be paid by fairs. In Wellington, NZ and Chicago, US, this is 50%, leading to some pretty high fares or low service.

Just having transit makes revenue though, in taxes from the increased commerce. Access to transport is also the single largest factor in escaping poverty. It's difficult to measure those numbers in revenue though.

But transport always must be subsidized by the State, going back to the roads of Rome.