In many places, buses, trains, and even ferries are part of a public transportation system. While users may need to pay to use these options, passenger fares are greatly subsidized by tax dollars. Public transportation is generally organized to benefit the public good, and its services are necessarily limited by the amount of revenue it receives. As such, in many areas public transportation operates only during certain hours and days, and there may be many areas in which public transportation is not available. If a traveler is trying to decide between using private and public transportation, he or she will need to consider whether public transportation operates in the area where he or she wishes to visit.